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Airports and environmental sustainability: a comprehensive review

Fiona Greer 1,2 , Jasenka Rakas 1 and Arpad Horvath 1

Published 8 October 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd Environmental Research Letters , Volume 15 , Number 10 Citation Fiona Greer et al 2020 Environ. Res. Lett. 15 103007 DOI 10.1088/1748-9326/abb42a

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1 Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, United States of America

2 Author to whom any correspondence should be addressed.

Fiona Greer https://orcid.org/0000-0001-9453-0640

Jasenka Rakas https://orcid.org/0000-0001-9694-3588

• Received 23 June 2020
• Accepted 1 September 2020
• Published 8 October 2020

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Method : Single-anonymous Revisions: 2 Screened for originality? Yes

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Over 2500 airports worldwide provide critical infrastructure that supports 4 billion annual passengers. To meet changes in capacity and post-COVID-19 passenger processing, airport infrastructure such as terminal buildings, airfields, and ground service equipment require substantial upgrades. Aviation accounts for 2.5% of global greenhouse gas (GHG) emissions, but that estimate excludes airport construction and operation. Metrics that assess an airport's sustainability, in addition to environmental impacts that are sometimes unaccounted for (e.g. water consumption), are necessary for a more complete environmental accounting of the entire aviation sector. This review synthesizes the current state of environmental sustainability metrics and methods (e.g. life-cycle assessment, Scope GHG emissions) for airports as identified in 108 peer-reviewed journal articles and technical reports. Articles are grouped according to six categories (Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Material and Resources, Multidimensional) of an existing airport sustainability assessment framework. A case study application of the framework is evaluated for its efficacy in yielding performance objectives. Research interest in airport environmental sustainability is steadily increasing, but there is ample need for more systematic assessment that accounts for a variety of emissions and regional variation. Prominent research themes include analyzing the GHG emissions from airfield pavements and energy management strategies for airport buildings. Research on water conservation, climate change resilience, and waste management is more limited, indicating that airport environmental accounting requires more analysis. A disconnect exists between research efforts and practices implemented by airports. Effective practices such as sourcing low-emission electricity and electrifying ground transportation and gate equipment can in the short term aid airports in moving towards sustainability goals. Future research must emphasize stakeholder involvement, life-cycle assessment, linking environmental impacts with operational outcomes, and global challenges (e.g. resilience, climate change adaptation, mitigation of infectious diseases).

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List of acronyms

1. introduction.

Airport infrastructure is a vital component of society's transportation network. There are more than 40 000 airports worldwide (CIA 2016 ). Around 2500 airports processed over 4 billion passengers in 2018 (IATA 2018 ). The onset of COVID-19 has drastically decreased air traffic levels (IATA 2020 ). It is likely that air travel will recover over the next couple of years and continue to rise. In the United States, massive investment is required (ASCE 2017 , ACC 2020 ) to modernize and retrofit aged, inadequate airport infrastructure (e.g. terminals, airfields, service equipment). Similar expansion projects and necessary reconfiguration projects for post COVID-19 processing of passengers are occurring worldwide. Airports are not solely transport nodes. The onset of 'airport cities' make this critical infrastructure a catalyst for economic, logistical, and social development (Appold and Kasarda 2013 ).

The environmental impacts attributed to airport construction and operational activities (e.g. building operation, ground service equipment (GSE)) are significant to consider, especially in light of the fact that as other transport sectors go 'green,' the air transport sector will face more challenges in reducing their environmental impacts. It is estimated that the aviation industry accounts for approximately 2.5% of global greenhouse gas (GHG) emissions in 2018 (IEA 2019 ), but that estimate excludes the impacts from airport construction and operation. An analysis of 2019 data for San Francisco International Airport (SFO 2018 , 2020 ) reveals an approximate annual breakdown of 85% for aviation GHG emissions and 15% for airport GHG emissions. Although not accounting for life-cycle impacts and not representative of every airport, this breakdown offers a sense of scope of how GHG impacts are divided between aviation (i.e. flights) and airport activities. The environmental impact of airport infrastructure/operations is not just limited to their GHG emissions. Airport construction and operation also results in emissions of air pollutants such as carbon monoxide (CO), nitrogen oxides (NO x ), and particulate matter (PM), displacement of and damage to natural ecosystems, generation of waste, and consumption of resources such as water.

In the public policy sphere, airport sustainability is an emerging area of interest. The aviation and airport communities recognize the important role that airport infrastructure plays in promoting beneficial environmental and human health outcomes. However, how the public sector addresses airport sustainability is fragmented and lacks rigorous appraisal of suggested best practices. Oftentimes, airport operators rely on other airports' existing sustainability guidelines for selecting 'green' practices that are not explicitly defined and quantified (Setiawan and Sadewa 2018 ). This review offers the public aviation sector, in particular, a much-needed overview of relevant sustainability indicators and methods for airport infrastructure and guidance in pursuing future research and implementation of sustainable practices and projects.

The expected increase in demand for air travel and the necessary upgrades for airport infrastructure compound the environmental impacts of airport construction and operation. In designing and operating the next generation of airport infrastructure (e.g. terminal buildings) there must be a systematic way for evaluating the resulting environmental impacts. Measures that assess the sustainability of the design, construction, and operation of airport infrastructure offer a potential solution for airport operators to consider.

1.1. History and background

Sustainability, as defined in the United Nations' Brundtland Report, states that present society must manage and consume resources so as not to compromise future society's needs (Brundtland et al 1987 ). While the Brundtland definition acknowledges human activity's environmental impact, it does not offer concrete guidance for achieving sustainability. A less abstract framework is the 'triple bottom line' approach, which aims to identify solutions that balance environmental, social, and economic interests (Elkington 1994 ).

Sustainability indicators, or metrics, can be used to measure the 'sustainability performance' of an airport. Metrics are critical because they allow for:

• Comparing the sustainability of one airport (or one type of airport) against another;
• Identifying the weak points or opportunities for improvement in airport infrastructure;
• Measuring progress towards meeting targeted goals.

A standardized, empirical metric is also crucial for making decisions about sustainable design and operation of airport infrastructure (Longhurst et al 1996 ). Stakeholder involvement in developing these indicators is necessary (Upham and Mills 2005 ). Sustainability metrics are a component of a larger-scale sustainability plan. Ideally, formalized sustainability plans developed by airports should incorporate metrics for tracking progress towards goals.

Airport sustainability, as defined by the aviation industry, incorporates the 'triple bottom line' concept with a fourth pillar focused on operational efficiency. Airport Council International (ACI) refers to this approach to sustainability as EONS (Martin-Nagle and Klauber 2015 , Prather 2016 ). Common subcategories of EONS are shown in table 1 . An important research dimension of the airport industry is the U.S. National Academies of Sciences' Airport Cooperative Research Program (ACRP), which researches and publishes synthesis reports and guidance for current sustainability practices at airports. ACRP reports are largely compiled through literature reviews of airports' published sustainability reports and through interviews, surveys, and questionnaires with airport operators. Recent topics of ACRP reports include:

• overall sustainability (Brown 2012 , Delaney and Thomson 2013 , Lurie et al 2014 , Prather 2016 , Malik 2017 );
• feasibility of on-site energy provision (Lau et al 2010 , Barrett et al 2014 ) and microgrids (Heard and Mannarino 2018 );
• GHG emission reduction strategies (ACRP, FAA, Camp, Dresser, & McKee et al 2011 , Barrett 2019 );
• air quality impacts (ACRP, FAA, CDM Federal Programs Corporation et al 2012a , ACRP 2012b , Lobo et al 2013 , Kim et al 2014 , 2015 )
• water efficiency (Krop et al 2016 ) and stormwater management (Jolley et al 2017 );
• habitat management (Belant and Ayers 2014 );
• sustainable ground transport (Kolpakov et al 2018 );
• sustainable construction practices (ACRP, FAA, Ricondo & Associates et al 2011 );
• waste management (Turner 2018 );
• climate change adaptation of airports (Marchi 2015 ).

Table 1.  Airport industry concept of sustainability or EONS, as defined by Prather, 2016.

The definition of environmental airport sustainability in the academic literature varies with some defining it according to multiple categories of environmental impacts (Chao et al 2017 , Ferrulli 2016 , Gomez Comendador et al 2019 ; Kilkis and Kilkis 2016 ) and others limiting that definition to traditional environmental aviation impacts such as emissions and noise (Lu et al 2018 ). Environmental sustainability is assessed using both quantitative and qualitative metrics/measures, and using both generalized, average airports (Chester and Horvath 2009 ) and data from operating airports (Chao et al 2017 ; Kilkis and Kilkis 2016 , Li and Loo 2016 ).

In both industry and academic research, environmental impacts are often disaggregated according to the airside and landside components of the airport system boundary. Figure 1 shows a plan view schematic of the typical features included in the airport system boundary. It should be noted that energy generation, water/wastewater (WW) treatment, and waste management infrastructure can be located within airport-owned property (i.e. decentralized) or within the surrounding community of the airport (i.e. centralized). Table 2 identifies the purpose and primary stakeholders for each airport component. Understanding the scope of airport infrastructure aids in identifying the most relevant environmental impacts and the stakeholders best equipped to mitigate those impacts.

Figure 1.  Plan view of airport system boundary. Key infrastructure features are identified.

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Table 2.  Purpose and primary stakeholders of key airport infrastructure.

1.2. Research objectives and goals

While previous studies have examined sustainability practices of individual airports (Berry et al 2008 , Prather 2016 ), this work represents the first comprehensive systematic review of academic and industry literature on airport environmental sustainability. The five objectives of this research are: (1) synthesize the existing literature on environmental sustainability indicators and metrics for airports; (2) review the application of sustainability indicators developed for the construction of terminals and other airport facilities at a case study airport (San Francisco International Airport also known as SFO); (3) identify gaps in the literature; (4) recommend what sustainability indicators/metrics should be employed at airports based upon the results of the literature review; (5) provide recommendations for future directions of research. Sustainability indicators are grouped according to the SFO framework: Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Materials and Resources. These five categories provide a framework for stakeholders to begin exploring the scope of relevant environmental impacts. The breadth of the five categories also highlights that sustainability encompasses more than one type of impact (e.g. GHG emissions) and underscores that airports have multiple priorities in addressing their environmental impacts. The expected outcome from this review is the identification of gaps in the existing literature and practice as it pertains to evaluating the sustainability of airport infrastructure. Recommendations for future research directions will provide those in the academic realm, as well as in the public aviation sector, a robust assessment of what metrics, practices, and methods should be applied to achieve optimal performance outcomes.

1.3. Overview of article

Section 2 presents the methodology for conducting the systematic review. Section 3 follows with a characterization, trend analysis, and synthesis of the reviewed literature, along with a review of the sustainability indicators used at a current SFO infrastructure project. Section 4 discusses the limitations and gaps of the existing literature, analyzes the efficacy of SFO's sustainability assessment framework, and provides guidance for future research directions. Section 5 concludes with a summary of the overall work and a recommendation for practices that airports should implement in the short term.

2.1. Systematic literature review

2.1.1. criteria for selecting research papers.

The foremost criterion in selecting peer-reviewed research articles and technical reports is that they pertain to indicators (i.e. metrics or measurements) for environmental sustainability. Although the concept of sustainability also includes economic and social factors, they are outside the scope of this review. We excluded corporate sustainability reports published by individual airports as data from these reports often appear in non-standard formats. However, individual airport sustainability practices were explored as part of the review of academic and ACRP literature. We iteratively searched for peer-reviewed research articles and technical reports in Web of Science, Google Scholar, and the National Academies of Science' ACRP database that were relevant to 'airport sustainability,' using the key terms of 'airport' and variations of 'sustainability' including 'environmental sustainability,' 'sustainable development,' and 'environmental impact.'

Searches were conducted with key terms related to the five categories of the SFO framework (i.e. Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Materials and Resources). Additional searches also included articles that incorporated life-cycle assessment (LCA), a method for assessing the 'cradle-to-grave' environmental impacts of a product, process, or project. We elected to also include search terms for Scope 1, Scope 2, and Scope 3 GHG emissions. Table 3 summarizes the definitions and examples of Scope GHG emissions.

Table 3.  Summary of GHG scope emissions for airports.

Characterizing GHG emissions according to the three Scopes aligns with airport industry practice of allocating responsibility for GHG emissions among airport stakeholders (ACA 2020 ). Exact search terms for all criteria are provided in table A1 in appendix A (available online at https://stacks.iop.org/ERL/15/103007/mmedia ). Articles that were relevant to at least more than one of the five sustainability categories were considered as part of a Multidimensional category.

Articles that focused on sustainability indicators for the construction and operation of physical airport infrastructure were prioritized. Articles were excluded if they concentrated on aircraft, aircraft fuel, or on aircraft operations within the airport boundary such as taxiing, queuing, and the landing and take-off (LTO) cycle. The rational for this exclusion is that aircraft-related sustainability is an already extensively reviewed subject (Agarwal 2010 , Blakey et al 2011 , Sarlioglu and Morris 2015 ). However, articles pertaining to aircraft servicing operations at airports (e.g. ground service equipment or GSE, de-icing) were included. All screening criteria are listed in table A2 in appendix A. Note that the time period of 2009 to 2019 is selected to provide a meaningful analysis of the academic literature, as interest in airport environmental sustainability as a research field began in earnest at the end of the 2000s.

The searches yielded a total of 108 articles grouped according to Energy and Atmosphere ( n = 22), Comfort and Health ( n = 25), Water and Wastewater ( n = 14), Site and Habitat ( n = 16), Materials and Resources ( n = 18), Multidimensional ( n = 13). Common themes of sustainability indicators for each category are depicted in figure 2 . A bibliography for all articles included in this systematic review is provided in appendix A (table A3). Section 3 provides a trend analysis of the articles included in the systematic review.

Figure 2.  Themes for each of the five sustainability categories.

3.1. Characterization of systematic literature review

A trend analysis of the reviewed articles indicates that interest in airport environmental sustainability has steadily increased over the period of 2009 to 2019 (figure 3 ). Article counts in each category theme (figure 4 ) reveal that research among the various categories is relatively balanced, with some prominent exceptions. Article counts for 'Ambient Air Quality,' 'Airfield Materials,' and 'Multidimensional' research themes are the highest. The high article counts for 'Ambient Air Quality' and 'Airfield Materials' suggests that research in the field of airport environmental sustainability largely focuses on the characteristics of an airport that are most prominent and apparent (i.e. the runway, taxiway, and apron). The high article count for the 'Multidimensional' category indicates that the research community is beginning to recognize that airport sustainability is comprised of multiple environmental impacts across multiple airport functions. In categories such as 'Waste Management' and 'Building Materials,' the small article counts imply that these specific subjects are still emerging as relevant research areas.

Figure 3.  Cumulative articles by year (dotted line = moving average).

Figure 4.  Cumulative articles by theme.

3.1.1. Synthesis of research by category

3.1.1.1. energy and atmosphere.

Common themes among the articles featured in the Energy and Atmosphere category include energy management of airport infrastructure, use of renewable energy on-site, and energy-related air emissions.

3.1.1.1.1. Energy management

Energy management refers to a process by which airports can characterize and monitor their energy consumption and enact measures to reduce it. Airports use fossil fuels (natural gas, petroleum) and electricity to perform various operational requirements such as controlling the thermal environment of buildings, lighting runways and buildings, and fueling airport ground equipment and vehicles. Using Seve Ballesteros-Santander Airport in Spain as a case study, it is estimated that most of the energy consumption at an airport is attributable to the terminal building with heating, ventilation, air conditioning (HVAC) and lighting being the most energy-intensive practices (Ortega Alba and Manana 2017 ). A best practice for energy management is implementation of an energy monitoring system (Lau et al 2010 ). Although not analyzed from an environmental perspective, airports represent an opportunity for exploring the implementation of microgrids, which allow for on-site energy generation and storage (Heard and Mannarino 2018 ).

Some literature indicates that if an airport has implemented specific energy management practices, then those practices are a marker of sustainability. A sample of practices that are considered sustainable and have been implemented at two case study airports (Baxter et al 2018a , 2018c ) is provided in table 4 . An airport that implements a standardized energy management system is considered to be sustainable (Uysal and Sogut 2017 ). Implementation of specific practices depends upon site characteristics including climate, occupancy level, and operating hours (Malik 2017 ). An analysis of energy related to the lighting of a Turkish airport terminal indicates that indoor lighting is a critical energy consumer (Kiyak and Bayraktar 2015 ).

Table 4.  Example energy conservation practices at airports as reported in Baxter et al ( 2018a , 2018c ).

3.1.1.1.2. Renewable energy

Implementation of on-site renewable energy is another typical indicator of sustainability as discussed in the literature. There are safety concerns (e.g. glare, radar interference) with some forms of renewable energy such as solar and wind (Barrett et al 2014 ), but airports are ideal candidates for employing on-site renewables because of their expansive land areas (Lau et al 2010 ). Metrics for evaluating the efficacy of on-site renewable energy such as solar photovoltaic (PV) systems include percentage of energy demand met by on-site renewables (Dehkordi et al 2019 ) and exergy (Kilkis and Kilkis 2017 , Sukumaran and Sudhakar 2018 ). Exergy, as it relates to provision of on-site solar PV, refers to the quality of the energy delivered; solar power tends to have high thermal losses unless cooling intervention is taken. In assessing the emissions impact from different energy sources in a district heating system at Schiphol Airport in the Netherlands, it is argued that GHG emissions should be estimated by accounting for both the first and second laws of thermodynamics (Kilkis and Kilkis 2017 ). Accounting for GHG emissions from both the quantity (first law) and quality (second law) of energy provides a more realistic analysis of the feasibility for achieving practices that are considered sustainable (e.g. net zero-carbon airport terminal buildings). Another metric for assessing environmental impacts from renewable energy at airports is absolute reduction of fossil fuel consumption, which is applied to evaluate a solar PV and battery storage project at Cornwall Airport Newquay in the United Kingdom (Murrant and Radcliffe 2018 ). Modeling of a solar PV farm at a rural U.S. airport indicates that this form of renewable energy can meet both the airport's and local community's electricity needs without compromising pilot or airspace safety (Anurag et al 2017 ). A groundwater source heat pump was found to meet indoor thermal requirements in a more energy-efficient manner (i.e. a higher coefficient of performance) than conventional heat pumps for a Tibetan airport (Zhen et al 2017 ). LCA is used to inventory the GHG emissions from using a biomass-fired combined heat and power plant at London Heathrow Airport to meet terminal building heating needs (Tagliaferri et al 2018 ).

3.1.1.1.3. Energy-related emissions

Recommended GHG emission reduction strategies related to energy use at airports pertain to designing building envelopes to be more energy efficient, using energy efficient equipment and fuels, relying on renewable energy, and managing use of refrigerants (ACRP, FAA, McKee, Dresser Camp, & Synergy Consulting Services 2011 , Barrett 2019 ). GHG emissions from annual airport energy consumption are a typical sustainability evaluation metric (Monsalud et al 2015 , Baxter et al 2018a , 2018c ). In practice, GHG emissions are often inventoried according to a framework developed by ACI, which recognizes that an airport is under direct control of GHG emissions from Scope 1 sources (e.g. on-site power generation) and Scope 2 sources (e.g. purchase from grid electricity), and only able to influence Scope 3 sources (e.g. emissions from an airline's GSE) (ACRP, FAA, Camp, Dresser, & McKee et al 2011 , Ozdemir and Filibeli 2014 ). The ACI framework accounts for the annual amount of electricity and natural gas consumed and the amount of fuel used to power airport ground vehicles. A similar method allocates emissions to each macro unit (e.g. GSE) at an Italian airport (Postorino and Mantecchini 2014 ). A more holistic approach for measuring an airport's energy consumption accounts for the loss of a carbon sink from the deforestation of the site on which Istanbul International Airport was built (Kılkış 2014 ).

3.1.1.2. Comfort and health

The Comfort and Health themes in the literature include building occupant comfort and health impacts related to ambient and indoor air quality.

3.1.1.2.1. Building occupant comfort

Passengers and airport/airline employees spend a considerable amount of time inside airport buildings such as terminals, maintenance facilities, and control towers. Occupant comfort in these buildings is relevant for environmental sustainability because aspects of comfort (i.e. thermal, ventilation, lighting) are directly related to metrics such as energy consumption. Research into novel air conditioning and heating systems in terminals at Chinese airports indicates that thermal and ventilation comfort can be satisfied while saving energy (Meng et al 2009 , Zhang et al 2013 , Zhao et al 2014 ; Liu et al 2019). An investigation of preferences at airports in the U.K. demonstrates that occupants tolerate higher thermal levels and prefer natural lighting, which have energy-saving implications (Kotopouleas and Nikolopoulou 2018 ). Designing airport buildings to emphasize natural lighting should incorporate the functional operational characteristics of air travel (i.e. operational peaks occur in the early morning and early to late evening) (Clevenger and Rogers 2017 ).

3.1.1.2.2. Indoor air quality

Exposure to air pollutants is known to cause negative human health impacts including increased risk of respiratory illness, cardiovascular disease, and death (Apte et al 2012 , Kim et al 2015 ). Indoor air quality (IAQ) research focuses on the pollutants and factors (e.g. ventilation systems, building design) that contribute to occupant exposure while inside facilities such as terminals and control towers. Research on exposure in indoor settings at airports has been limited to the concentrations of nitrogen dioxide (NO 2 ) and volatile organic compounds (VOCs) in a maintenance room at a Lebanon airport (Mokalled et al 2019 ), PM in a terminal building at a Chinese airport (Ren et al 2018 ), VOCs, PM, odorous gases, and carbon dioxide (CO 2 ) at an Italian airport terminal (Zanni et al 2018 ), and CO, VOCs, and PM in a control tower at a Greek airport (Helmis et al 2009 , Tsakas and Siskos 2011 ). One study linked IAQ at eight large Chinese airports with passenger satisfaction, finding that IAQ satisfaction is correlated with CO 2 concentration (Wang et al 2015 ).

3.1.1.2.3. Ambient air quality

Ambient, or outdoor, air quality at airports is a function of both aircraft and non-aircraft operations. Sources of non-aircraft emissions include the equipment used to clean, load, or reposition parked aircraft (i.e. GSE) or used to provide power to parked aircraft (i.e. ground power units or GPUs). Another source of emissions from parked aircraft is the auxiliary power unit (APU), an external rear engine on the aircraft which provides electrical power and thermal conditioning (ACRP , 2012b , Lobo et al 2013 ). Other outdoor sources include emissions from construction (Kim et al 2014 ) and operation of airport ground access vehicles (e.g. maintenance trucks, firetrucks). Much of the exposure to pollutants such as black carbon (a component of PM) occurs on the airfield's apron where aircraft are often positioned for passenger boarding and luggage loading (Targino et al 2017 ). Outdoor exposure to VOCs near a U.S. airport revealed higher-than-expected concentrations of toluene (Jung et al 2011 ). Construction of a terminal building at a major airport in Spain was a critical contributor to ambient levels of PM (Amato et al 2010 ).

A review of airport contributions to ambient air pollution suggests that research on emissions related to GSE, GPU, and APU operations is more limited relative to research on emissions from aircraft (Masiol and Harrison 2014 ). Concentrations of CO 2 , CO, PM, hydrocarbons, NO x , sulfur dioxide, sulfate, and black and organic carbon are estimated for APU and GSE use at 20 U. K. airports (Yim et al 2013 ), emissions of CO, hydrocarbons, and NO x from APUs and GSE are calculated for turnaround operations at major European airports (Padhra 2018 ), and concentrations of NO x and PM for APUs and GSE at Copenhagen Airport are calculated (Winther et al 2015 ). Provision of fixed electrical power and external air conditioning units is considered a sustainable solution for mitigating PM and NO x emissions from APU, GPU, and GSE operation (ACRP, 2012a , Yim et al 2013 , Winther et al 2015 , Padhra 2018 , Preston et al 2019 ). Use of alternative fuel (hydrogen) for powering GSE is considered another sustainable measure to improve ambient air quality on the airport apron (Testa et al 2014 ).

3.1.1.3. Water and wastewater

The major themes related to Water and Wastewater in the reviewed articles include water conservation strategies at airports and water quality concerns related to airport activities.

3.1.1.3.1. Water conservation

Airports consume water for indoor operations such as toilet-flushing, food preparation, and HVAC systems and for outdoor operations including irrigation and aircraft/infrastructure washing and maintenance (Krop et al 2016 ). The amount of water that major airports consume is not insignificant, and is on par with consumption patterns of small and medium-sized cities (de Castro Carvalho et al 2013 ). A typical metric for assessing airport water consumption is volume per day (Baxter et al 2019 ), but this metric fails to offer a broader picture of what sources of water are consumed and what management practices yield the best results (Couto et al 2013 ). The water conservation techniques proposed for airports include monitoring of water consumption, use of water efficient fixtures/fittings, reducing irrigation demand, and use of alternative water sources (e.g. rainwater, greywater, recycled wastewater).

An important point in the literature is that much of airport water consumption is for activities that do not require potable water. There is an opportunity for airports to rely upon alternative sources of water which have been studied for: rainwater harvesting at an Australian airport (Somerville et al 2015 ); wastewater reclamation for a Brazilian airport (Ribeiro et al 2013 ); greywater usage at a Brazilian airport (Couto et al 2013 , 2015 ); seawater and greywater use at an airport in Hong Kong (Leung et al 2012 ). These studies assess the efficacy of alternative sources in terms of demand met.

3.1.1.3.2. Water quality

Water quality concerns related to airport activity can be categorized as persistent, seasonal (e.g. from de-icing operations), and accidental (e.g. fuel spills) (Baxter et al 2019 ). Airports make efforts to prevent hazardous pollutants and fluids from entering groundwater or surface water bodies. Stormwater management strategies include use of bioretention basins, green roofs, harvesting, porous pavement, sand filters, and wetland treatment systems (Jolley et al 2017 ). The academic literature focuses on water quality issues stemming from de-icing activities, a necessary operation for aircraft and runways in cold-weather climates. De-icing fluid runoff can create negative surface water quality effects that impact aquatic flora and fauna by causing higher levels of chemical oxygen demand and lower levels of dissolved oxygen (Fan et al 2011 , Mohiley et al 2015 ). Potential mitigation measures for managing aircraft de-icing include utilization of novel soil filters (Pressl et al 2019 ) and treatment with constructed wetlands (Higgins et al 2011 ). Most studies assess the water quality impact of de-icing fluid, but one article examined the GHG impact from forgoing collection and treatment of de-icing fluid at a wastewater treatment plant and instead using on-site recycling (Johnson 2012 ).

3.1.1.4. Site and habitat

Major themes of the Site and Habitat category in the literature refer to the impact airport construction and operation have on existing natural ecosystems, the effects from on-site and public transportation options, and the implications of airport resilience to climate change.

3.1.1.4.1. Site

Airport development and operation requires suitable land area. In regions where existing land is not suitable, land reclamation is used to create a suitable airport environment. Research into the effects of land reclamation on existing ecosystems focus on impacts to soil, water, air, and animal species (Yan et al 2017 ; Zhao et al 2019 ). Another indicator in the literature refers to efficiency of airport land utilization, or how many aircraft operations occur per given unit area (Janic 2016 ). Airport operation and its impacts on wildlife populations is another area of research, with the goal of finding specific strategies to discourage and accommodate wildlife populations on airfields, airport water resources, terminal buildings, and control towers (Belant and Ayers 2014 ). Work done in the academic literature focuses on identifying the factors that attract avian species to green roofs (Washburn et al 2016 ), on the impacts of solar arrays on avian species (Devault et al 2014 ), and on the effects of airport expansion on bat populations (Divoll and O'Keefe 2018 ).

3.1.1.4.2. Transportation

Sustainable transportation, as it relates to airports, refers to the modes of transportation for shuttling passengers from terminals to parked aircraft and for bringing passengers to airports. Common sustainability practices for on-site transportation include: use of alternative vehicles (e.g. electric vehicles); restriction of vehicle idling; and reducing the number of empty trips (Kolpakov et al 2018 ). One study examined the use of an underground rapid transport system (URTS) for transporting airport passengers the long distances from main terminal buildings to satellite and midfield concourse terminals (Liu and Liao 2018 ). This study did not include specific environmental indicators, but noted that use of URTS is sustainable because it frees up congestion from passenger transport on the airfield concourse. Sustainable public transport options might include using automated vehicles (Wang and Zhang 2019 ), encouraging passengers to use existing public transport options by enhancing their capacity, discouraging private vehicle use, integrating with other transport hubs (Budd et al 2016 ), or installing dedicated electric vehicle charging infrastructure (Silvester et al 2013 ).

3.1.1.4.3. Resilience

The resilience of airports to climate change impacts is a significantly under-researched subject. Relevant risks that airports in coastal locations will face include impacts from sea-level rise and increased frequency of flooding events (Marchi 2015 , Burbidge 2016 , Poo et al 2018 ). Another site implication related to climate change is that increased mean air temperatures will make it harder for aircraft to generate lift, thereby necessitating the construction of longer runways (Coffel et al 2017 ).

3.1.1.5. Materials and resources

Themes from the literature for Materials and Resources center around selection of materials for the construction of airfield (e.g. runway, taxiway, apron) and terminal building infrastructure, as well as management of waste from airport construction and operation.

3.1.1.5.1. Airfield materials

Estimation of environmental effects of airfield pavements is a fairly well-researched subject area, relative to other airport infrastructure. Airfields are either made from asphalt or concrete, which are known major sources of GHGs (Horvath 2004 , Santero et al 2011 , Miller et al 2016 ). The sustainability of airfield pavements is constrained by structural integrity requirements and safety standards (Pittenger 2011 ).

Evaluation metrics for sustainable airport pavement can be general, such as implementing suggested best practices, including: using recycled aggregate in pavement mixes; using locally sourced construction materials; reducing idling times of construction equipment (Hubbard and Hubbard 2019 ). More specific critical factors of a sustainable airport pavement relate to its construction (i.e. the raw materials and equipment used, transportation, waste management) and its operation, which is a function of the pavement's structural characteristics (Babashamsi et al 2016 ). Table A4 in appendix A highlights the specific sustainable practices and assessment methods/metrics found in the literature as they pertain to different parts of the airfield. Example sustainable practices include use of supplementary cementitious materials (SCM) in concrete runways and use of recycled aggregates in taxiway and apron construction. LCA is frequently used in measuring the environmental sustainability of airfield pavements. The scope of most of the LCAs is limited to impacts from the raw material and construction phases of the airfield.

3.1.1.5.2. Building materials

Relative to the airfield, environmental impact analysis of other airport infrastructure (e.g. terminal buildings) is much more limited. LCAs have been performed to determine the optimum level of thermal insulation for terminal buildings at two Turkish airports with a focus on selecting a design that reduces GHG emissions (Akyuez et al 2017 , Kon and Caner 2019 ). An extensive overview of construction methods and building materials that are standard practice (e.g. using locally sourced materials) among the green building community is applied for airports (ACRP, FAA, Ricondo & Associates, R. &, Center for Transportation, C. for, & Ardmore Associates 2011 ). It is common practice, as mentioned in the ACRP literature, for airports to aim for green building certification from groups such as the U.S. Green Building Council's Leadership and Energy in Environmental Design (LEED) like LEED provides a checklist framework where building owners (municipalities in the case of airports) earn points for choosing 'green' building materials and design attributes, among other criteria. There are over 200 LEED certified airport buildings worldwide (USGBC 2020 ), with SFO's Terminal 2 the first LEED Gold airport terminal in the U.S. (SFO 2011 ).

3.1.1.5.3. Waste management

Analysis of waste management at airports is another emerging research area. Waste sources at airports include food waste from retailers/concessionaires, construction waste, and aircraft-related waste (Turner 2018 ). Metrics applied for analyzing waste at a major international airport include quantity of waste, waste source fraction, and waste amount per operation (Baxter et al 2018b ). One article assessed the life-cycle impact, in terms of air emissions, of six waste management scenarios at Hong Kong International Airport determining that on-site incineration with heat recovery yielded optimal results (Lam et al 2018 ).

3.1.1.6. Multidimensional studies

Sustainability, as expressed in ACRP reports (Brown 2012 , Delaney and Thomson 2013 , Lurie et al 2014 , Prather 2016 , Malik 2017 ), encompasses many categories including energy and climate, water, waste, natural resources, human well-being, transportation, and building design and materials. Many of the metrics that the ACRP literature use to assess the specific categories of sustainability mirror those described in the academic literature. A theme among the ACRP work is the evaluation of sustainability practices from an economic and practical perspective, recognizing that implementation can yield economic benefit but takes concerted, coordinated effort.

Table 5 identifies metrics used for quantifying impacts and strategies used to reduce impacts. These metrics and strategies are extracted from the multidimensional journal articles included in the systematic review. Each metric or strategy is prioritized to the one of the five categories of interest. While the focus of this review paper pertains to metrics/strategies that evaluate the sustainability of physical airport infrastructure, and not does focus on environmental impacts related to the aircraft LTO cycle, some of the multidimensional papers include indicators for evaluating those specific environmental impacts (e.g. noise from near-airport aircraft operations). The indicators in table 5 range from explicit, quantifiable metrics (e.g. tonnes CO 2 per passenger) to more vague best practices (e.g. conserve energy in airport buildings). The metrics and strategies that are explicit and quantifiable are more informative for enacting policy measures than are vague strategies such as 'conserve energy' or 'reduce emissions.' It is also more effective for metrics and strategies that connect environmental impacts to operational outcomes and level of service (e.g. number of passenger-miles traveled). Connecting impacts to level of service allows for airports to track how efficiently they are managing their impacts as numbers of operations increase.

Table 5.  Sustainability indicators from multidimensional papers.

a ISO 50 001 Certification = International Standard Organization's Energy Management System. b Airport Carbon Accreditation = ACI certification that recognizes an airport's efforts to manage CO 2 emissions. c ISO 40 001 Certification = International Standard Organization's Environmental Management System. d WLU = Work Load Unit, a standardized metric for airport operations in terms of number of passengers processed or mass of freight handled.

Indicators from each multidimensional paper do not always span all five categories of environmental sustainability, suggesting that consensus building on the definition of environmental sustainability needs to occur. The Energy and Atmosphere category dominates with metrics often related to reducing airport building and airfield energy consumption and air pollutant emissions. Of the eight journal articles included in table 5 , all include metrics for addressing noise pollution in the Comfort and Health category, but none provide explicit metrics for assessing indoor air quality for airport buildings. The indicators in the remaining three categories vary in level of specificity. As an example, in the Materials and Resources category, four of the articles suggest airports use 'green building materials' but only one article (Ferrulli 2016 ) identifies in some detail what that means.

A theme that emerges from the multidimensional papers are the different methods utilized in determining the overall sustainability of an airport. Utility-based methodologies are utilized in two of the multidimensional articles (Chao et al 2017 , Lu et al 2018 ) in the ranking of the most critical indicators by weights applied from expert opinion. Another method for assessing an airport's environmental sustainability is the application of a checklist-based point system where the most sustainable airport implements the most indicators with the highest level of points (Gomez Comendador et al 2019 ). One method incorporates cost-benefit analysis where each environmental indicator for an airport development project is transformed into a financial amount and the highest benefit-cost ratio yields the most sustainable outcome (Li and Loo 2016 ). A composite ranking indicator is created by normalizing indicators across all categories to compare the environmental sustainability of multiple airports (S. Kilkis and Kilkis 2016 ). Only one method applies life-cycle assessment in inventorying the environmental impact from the LTO cycle, APU and GSE operation, de-icing activities, lighting, and construction of an airport terminal, airfield, and parking lot (Chester and Horvath 2009 ).

The multidimensional articles that include case study airports are listed in table 6 , along with each airport's location. All of the case study airports are considered major international hubs, averaging millions of passengers per year. Their locations span the primary airport markets including Asia, Europe, and the United States, but do not reflect the emerging markets of Latin America and Southeast Asia. By comparing airports of a similar operational capacity, the multidimensional papers offer some insight into how varying regions influence environmental impact. However, more case study airports are necessary to capture local impacts. Insight is lacking on whether the sustainability indicators developed in these multidimensional articles result in distinct environmental outcomes for disparate levels of airport service (e.g. small, regional airports; medium hub airports). Modeling environmental impacts from an average airport (Chester and Horvath 2009 ) allows for generalization of results, which might yield more far-reaching outcomes (i.e. sustainability indicators can be applied to a greater range of airports).

Table 6.  Case study airports/locations from multidimensional papers.

3.1.2. Summary of trends in existing research

Figure 5 shows a word cloud diagram of the article titles included in each of five sustainability categories and the multidimensional category. Frequently used words appear larger relative to less frequently used words. Figure 5 provides a visual representation of the key themes for each category. A summary of key trends in the five sustainability categories and the multidimensional category include:

• Energy and atmosphere: Articles focus on investigating the efficacy of on-site renewable energy at various case study airports. Common sustainability indicators are total energy consumed and mass of GHG emissions from energy consumption. Best practices are considered as: monitoring of energy consumption; utilization of energy efficient HVAC equipment and lighting; installation of on-site renewable energy. There is some effort, particularly in the ACRP literature, to evaluate best practices from a practical perspective (e.g. addressing the safety implications of PV installations). Use of LCA in this category is limited.
• Comfort and health: Most of the research is focused on indoor comfort and health indicators like preferences for thermal and lighting conditions and concentrations of PM, VOCs, CO, and CO 2 . Studies on exposure to ambient air pollutants from non-aircraft sources are limited. Most of the research on ambient air quality aggregates emissions from all sources. There is recent effort to investigate the impact from non-aircraft sources such as APUs, GSE, and GPUs and to identify possible solutions for these equipment (e.g. use of external electrical power and air conditioning units).
• Water and wastewater: Articles focusing on estimating the potential utilization of alternative water sources at airports dominate. Water quality research pertains to impacts from stormwater and de-icing fluids. A typical article in the Water and Wastewater category includes annual water consumption per passenger or flight operation. There is discussion in the literature on whether a disaggregated metric (e.g. indoor water consumption per passenger, outdoor water consumption per passenger) might be a more effective performance indicator.
• Site and habitat: This category is the least explored in the literature. Few articles offer measurable indicators, with most of the quantifiable metrics relating to land use efficiency and destruction of wildlife habitat. There is need for quantifiable indicators for research in on-site, public/private transport and for climate change adaptation practices.
• Materials and resources: Research on the environmental sustainability of airfield pavements dominates this category. LCA is the most frequently used assessment methodology, with life-cycle GHG emissions and energy consumption the most common assessment metrics.
• Multidimensional: Research that investigates airport sustainability from a multidimensional perspective is grouped according to efforts by ACRP and by the academic community. ACRP largely defines environmental sustainability across the five categories (i.e. energy and atmosphere, comfort and health, water and wastewater, site and habitat, materials and resources), but often focuses on economic and practical factors of implementing sustainability best practices. These best practices are often identified through interviewing and surveying U.S. airports. Sustainability indicators in the academic literature predominantly focus on energy consumption and GHG emissions. Sustainability is assessed with a number of methodologies (e.g. utility-based theories, cost-benefit analysis, LCA), suggesting that within the academic community there is a lack of consensus on what attributes and indicators make an airport sustainable.

Figure 5.  Word cloud diagram of article titles included in systematic review. Frequently used terms appear larger relative to less frequently used terms.

3.2. Application of an airport sustainability assessment

This section reviews the application of the SFO environmental sustainability framework on an existing infrastructure project at the airport.

3.2.1. Selection of case study airport

San Francisco International Airport (SFO) is one of the United States' large hub airports and it serves major domestic and international routes. The airport ranked seventh among busiest airports in 2018, with enplanements totaling close to 28 million (FAA 2020b ). The airport was an early adopter in implementing sustainability efforts and in developing metrics to assess the sustainability of construction and operation of airport infrastructure projects (SFO 2020 , FAA 2020a ). A review of the implementation of SFO's sustainability framework answers two critical questions: (1) how sustainability efforts practically get implemented at airports, and (2) how their implementation is or is not effective in yielding measurable benefits. Featuring SFO as a case study offers stakeholders (e.g. regulators, airport operators, the public) insight into what is considered best practices, or acceptable methods, for managing environmental impacts for major international airports. Additionally, it provides some understanding of how sustainability measures at an airport like SFO might not work as well for other airport types (e.g. small hub, regional, general aviation, etc.).

3.2.2. Development of sustainability indicators

SFO is redeveloping their Terminal 1 as part of a capacity-enhancement upgrade for the entire airport; the upgrade will increase the terminal's total number of annual enplanements to 8.8 million. Sustainability indicators were developed in conjunction with SFO's planning, design, and construction guidelines as a measurable index for determining whether the Terminal 1 project will comply with the airport's overarching environmental goals (e.g. achieving GHG emission reductions relative to a baseline year). Each sustainability indicator is grouped according to relevant themes in the five categories of Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, and Materials and Resources. Indicators are either considered 'Mandatory Requirements' or 'Expanded Requirements.' 'Mandatory Requirements' outline metrics and practices that must be achieved according to applicable federal, state, regional building codes and city-wide mandates (e.g. meeting LEED requirements). 'Expanded Requirements' are voluntary metrics and practices that project participants (i.e. contractors) are obligated to implement where feasible. For example, a city-wide 'Mandatory Requirement' in the Energy and Atmosphere category mandates 40% reductions below 1990 GHG emissions by 2025. An example 'Expanded Requirement' calls for reduced GHG emissions from natural gas consumption by using automated HVAC systems.

3.2.3. Implementation of indicators

The indicators are intended to be used for the planning, design, construction, and operation/maintenance phases of airport facilities. An additional level of evaluation is applied to each 'Expanded Requirement.' Requirements are rated as 'Baseline,' 'Baseline Plus,' or 'Exceptional Project Outcome.' Per the previous 'Expanded Requirement' example, 'Baseline,' 'Baseline Plus,' or 'Exceptional Project Outcome' ratings would be given to 10%, 20%, and 30% reductions in GHG emissions, respectively. Such a rating system allows SFO to discern between project outcomes that are more 'sustainable' than others.

The results of an analysis of the projected reduction in annual GHG emissions per square meter from implementing Energy and Atmosphere 'Expanded Requirements' in SFO's Terminal 1 project are shown in figure 6 . The specific 'Expanded Requirements' include practices that rely on reduced natural gas and electricity consumption in terminal buildings (e.g. energy-efficient escalators, dynamic glazing, radiant heating and cooling). It is projected that these 'Expanded Requirements' will reduce Terminal 1's energy use intensity (EUI). The EUI indicates how much natural gas and electricity is consumed by buildings. By converting the EUI to an equivalent amount of GHG emissions per square meter, it can be shown that the GHG intensity of the Terminal 1 project will be less than the average of other SFO buildings. The blue bars in figure 6 show the amount of GHG emissions per square meter, while the dotted outline indicates the amount of annual GHG savings per square meter in the Terminal 1 project. The GHG emissions account for the upstream processes related to natural gas provision and electricity generation. See appendix B for the complete methodology in producing figure 6 . The savings represent an approximate 57% reduction relative to the average GHG intensity for all SFO airport building infrastructure.

Figure 6.  Reductions in GHG Intensity associated with implementing energy reducing 'Expanded Requirements' in Terminal 1 (T1) project relative to the SFO average. Savings are relative to 2018 data.

4. Discussion

4.1. limitations and gaps of existing research.

With few exceptions on airport energy (Kilkis and Kilkis 2017 , Tagliaferri et al 2018 ), overall sustainability (Chester and Horvath 2009 , 2012 , Taptich et al 2016 ), and airfield pavements, much of the research fails to holistically analyze the environmental impacts through supply chains and regional variations. While the ACRP literature provides a sample representation of current best practices at airports, its analysis is sometimes limited by the responses it receives from case-study airports. For both the ACRP and academic literature, analysis of sustainability indicators is often limited by the scope of a case-study airport, so it is difficult to link research results with suggested practice or policy outcomes.

The literature in the Energy and Atmosphere category lacks a broader understanding of how much energy is used at different airports, what it is used for, and where it comes from. Current estimates are limited by the number of existing case-study airports. With an exception (Ozdemir and Filibeli 2014 ), the academic literature limits its characterization of GHG emissions according to Scope 1, Scope 2, and Scope 3. This limitation in the literature indicates that there is a slight disconnect between the academic research community and the airport industry and stakeholders as the Scope characterization is how the industry thinks about and manages GHG emissions. Research that investigates different energy sources (e.g. solar; bioenergy) and energy provision strategies (e.g. grid versus on-site storage) is just beginning, and more effort in this area is needed. Additional gaps in the research include:

• Environmental impacts of energy consumption in terms of other pollutants besides GHG emissions;
• Environmental assessment of airports and supply chains using local and regional models and data (Cicas et al 2007 );
• Characterization and environmental impact assessment of energy consumption patterns for specific airport infrastructure and equipment by region (e.g. U.S. airport terminals are focused on food consumption; European/Asian airports serve as retail/recreational centers);
• Energy consumption impacts from construction of new airport expansion/retrofitting projects.

As with the Energy and Atmosphere category, research in the Comfort and Health category could be broadened to include more research and innovative and exploratory case studies. In light of COVID-19, more research is urgently needed to investigate how terminal building design and ventilation equipment might influence spread of infectious diseases. Ambient air quality research tends to aggregate sources, which makes it difficult to determine if mitigation policies are effective. Additional gaps in the research include:

• More human health-focused exposure studies related to operation of non-aircraft equipment, such as GSE, GPUs, APUs, and ground access vehicles;
• Investigation of air pollutant concentrations related to landside operations, such as passenger pick-up and drop-off;
• Research on human health impacts from airfield and terminal building maintenance, retrofit, and construction;
• Air quality impacts related to selection of different building materials and cleaning/daily maintenance procedures.

As suggested in the Water and Wastewater literature, assessing an airport's water consumption in terms of volume per day provides minimal insight. More research should be conducted to provide a thorough overview of disaggregated water consumption at the airport level so that sustainable practices can be implemented appropriately. A major gap in the literature is the complete lack of research into the linkage between water consumption, water quality, energy needed to convey, treat and heat water, and the resulting GHG and other environmental emissions and impacts. This water-energy nexus is particularly relevant in examining the environmental sustainability of using alternative sources of water at airports, especially with respect to potable versus non-potable demands and options.

Much of the literature in the Site and Habitat category lacks explicit, quantifiable sustainability indicators and there is vast room for investigation into the following gaps:

• Energy and environmental implications of constructing resilience infrastructure, such as sea walls and stormwater systems;
• Environmental impacts of onsite transportation systems, such as underground rapid transit systems;
• Overview of the types of suitable, environmentally efficient transportation modes within and outside of the airport boundary, which is dictated by airport configuration and location;
• Environmental trade-offs between site selection and terminal building orientation and layout of runways.

Research in the Materials and Resources category is predominantly focused on environmental impacts of airfield pavement construction and maintenance, with life-cycle energy consumption and GHG emissions as common metrics. Within the theme of airfield pavements, more research regarding innovative designs and maintenance techniques are warranted. There is a lack of understanding on what sustainable pavement practices can be implemented at airports of different operational capacities. Small and medium-sized airports might be good candidates for testing out innovative practices because their load or volume requirements tend to be smaller than those of larger airports. In terms of sustainable materials and design for airport buildings, research results are limited. In practice, it is more common for airports to strive for LEED certification of airport buildings. LEED, for practical purposes, is a relatively easy standard to implement, but is not sufficient for meeting quantified performance goals throughout the life cycle of airports. Additional gaps in the research include:

• Environmental impact of conventional and alternative construction materials in terminal building infrastructure;
• Sustainability impacts of supply chains and sourcing of airport construction materials;
• Deeper understanding leading to defensible actions on waste generation and waste management techniques at airports, especially in the context of waste-management policies such as 'zero-waste' and bans of single-use plastics.

A review of articles in the Multidimensional category indicates that there is no cohesive, agreed-upon definition of airport environmental sustainability. Gaps in the research include:

• Determining optimal methods for achieving overall environmental sustainability at an airport, also integrated with achieving specified city, regional-level, airline, or civil aviation targets;
• Integration of life-cycle, or holistic, thinking within a specified time horizon into decision making (e.g. should an airport implement an electricity-based strategy if the electricity is generated from fossil fuels?);
• Specifying environmental sustainability indicators in the context of airport operational safety;
• Investigating the overlap between environmental sustainability and airport resilience;
• Rigorous analysis of environmental sustainability and operational parameters;
• Integration of actions in achieving societal sustainable development (economic, environmental, social) with airport, airline, air traffic control, and in general, civil aviation goals.

4.2. Efficacy of case study application

A projected 57% reduction in annual GHG emissions per square meter from consuming natural gas and electricity on-site within the airport terminal buildings suggests that SFO's sustainability assessment indicators have the potential to be effective. A more meaningful expression of results would relate saved GHG emissions to the airport's level of service (e.g. GHG emissions per passenger or per revenue dollar). There are limitations to stating one airport's efforts as 'best practice.' It should be emphasized that applicability from the results of the case study are dependent upon local factors. For SFO, implementing energy-efficient strategies saves more GHG emissions because SFO's electricity is supplied from hydropower, which is less carbon-intensive relative to the state average. Utilizing low carbon-intensive energy is a key sustainability performance indicator. While post-facto analysis would be able to confirm actual GHG reductions from implementing 'Expanded Requirements,' the project is still ongoing. Some important observations can still be made regarding SFO's sustainability indicators.

In discussions with parties involved with the Terminal 1 reconstruction projects, having sustainability criteria at the outset of project development is crucial. All involved parties must be aware of their specific commitments. It is a good practice going forward for project contracts to incorporate strong sustainability performance indicators. SFO plans to integrate language more thoroughly into the Architectural and Engineering standards and guidelines that specifically align with two of SFO's guiding environmental priorities, namely climate change and human and ecological health. Regarding the former, the new contract language will explicitly require that decarbonization be reflected in project design and procurement. For example, instead of a voluntary consideration as part of an 'Expanded Requirement,' low-carbon structural steel would have to be selected as a building material.

The voluntary aspect of the framework (i.e. the 'Expanded Requirements') and the evaluation of 'Expanded Requirements' as baseline, baseline plus, and exceptional project outcome are rather subjective. Such subjectivity does not necessarily result in a completed project with the best environmental performance. Additionally, the SFO framework relies upon building codes that while they are 'state of the art' compared to building codes outside of California, represent a minimum standard. If interested in attaining a facility or project that meets a specified, quantifiable environmental outcome, the subjectivity of a rating system or checklist is not the most effective approach.

SFO's sustainability indicators do not explicitly consider the tradeoffs that potentially occur with prioritizing one criteria over the other; it is a rather static framework that could benefit from incorporating spatial and temporal factors. For example, electing to use a decentralized recycled water source (which is an 'Expanded Requirement' in the Water and Wastewater category) is sometimes an energy-intensive process which can result in increased GHG emissions while enhancing resilience. In this anecdotal example, there is a potential tradeoff between achieving water conservation and reducing GHG emissions. While the SFO framework might work well for an airport that explicitly prioritizes overarching goals (e.g. reducing GHG emissions and climate change impact), it might need to be reevaluated for airports that must equally consider sometimes conflicting environmental priorities.

4.3. Suggestions for direction of future research

The roadmap for future research of airport environmental sustainability emphasizes increased stakeholder involvement, more life cycle-based analysis, linkage of environmental impacts with operational outcomes, and addressing major challenges such as adaptation to climate change and mitigation of infectious diseases like COVID-19.

Airport environmental sustainability is often addressed at project scale. There is a need for investigating the larger role that airports have in impacting the environment, especially in the context of achieving city- and regional-level environmental outcomes that lead most directly to higher environmental quality of people and ecosystems. This ties in with stakeholder involvement because for sustainability indicators including GHG emissions, an airport only claims responsibility for Scope 1 and Scope 2 emissions. Airports often exclude ownership of Scope 3 emissions (e.g. emissions from an airline's GSE, without which there are no airports). The outcome of an airport excluding ownership of Scope 3 emissions is twofold: (1) it is more difficult to manage Scope 3 emissions, and (2) it is difficult to understand an airport's total GHG impact at the city/regional/state/national level, which is important for meeting larger-scale climate performance targets. Therefore, a broader analysis of how different stakeholders should be included in addressing environmental sustainability efforts is necessary.

Society faces important challenges such as adapting to climate change, mitigating the spread of pandemic-causing diseases, and enhancing environmental quality of people and ecosystems. An airport's role in addressing these challenges is largely undefined, but sure to be a significant one. It is imperative that thorough research on an airport's role in managing these challenges gets organized.

5. Conclusion

A comprehensive, systematic review of 108 peer-reviewed articles and technical reports related to assessing and measuring aspects of airports' environmental sustainability has been conducted. Articles have been characterized according to the following categories: Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Materials and Resources, Multidimensional. Along with a systematic review of academic literature, a review has been undertaken of the application of an existing airport sustainability assessment framework for a case study airport, SFO.

A broad conclusion from the systematic review is that interest in airport environmental sustainability as a research topic is steadily increasing, but that there is ample need for more investigation. Prominent research themes within the scope of airport environmental sustainability include analyzing the environmental impacts (namely GHG emissions) from airfield pavements and energy management strategies for airport buildings, but not from other components of airports and for other environmental emissions and impacts. There is a dearth of research on the impacts of indoor air quality at airports. In the research community, there appears to be a lack of consensus about the scope of environmental impacts that should be included when evaluating the overall sustainability of airports. GHG emissions from energy consumption are one of the most commonly used metrics in research focused on overall airport sustainability.

Methods for evaluating environmental impacts vary. Systems like the World Resource Institute's Scope 1, 2, and 3 designation for GHG emissions and the LEED system for buildings are well-represented in airport-industry practice. The Scope designation primarily divides responsibility for mitigating emissions between airports and airlines, creating a gap whereby airports cannot directly control all emission sources. LEED is a minimum standard that is not sufficient for meeting quantified performance goals throughout the life cycle and supply chains of airports.

Moving forward, the increased use of assessment methodologies such as LCA will be useful in guiding decision-makers and policy outcomes in a more robust, granular direction. In the academic literature, LCA is primarily used for evaluating the environmental impact of airfield pavement construction. However, LCA can and should be applied to evaluate all components of airport construction and operational activities and to guide decision-making as to what practices will yield optimal results. LCA is the only comprehensive, systematic methodology (defined in ISO 14040 and 14044) that estimates the entirety of life-cycle environmental impacts of a product, process, or service. This method is very useful for accounting for regional differences in impacts, for comparing among alternative strategies, and for identifying weak points or activities that result in the greatest environmental burdens. There are also economic and social aspects of LCA that are helpful for decision-makers. One LCA approach, Economic Input-Output LCA, can be used to evaluate the resources, energy, and emissions resulting from economic activity throughout a product's supply chain (Hendrickson et al 1998 ). There are efforts to use a life-cycle approach to focus on the social aspects of a product's impacts (Grubert 2018 ). While addressing the economic and social impacts from airports is beyond the scope of this review, the economic and social implications of airports are likewise very important and demand thorough investigations and actions.

In conjunction with LCA, future research should apply analysis that connects environmental impacts with operational parameters for specific airport occupant groups (e.g. ground handlers), airport infrastructure (e.g. apron), and airport scale (e.g. small, medium, large hubs). Accounting for operational parameters at different scales will provide a better understanding of how environmental sustainability efforts impact different stakeholders and the airport's primary function (i.e. processing passengers and cargo).

A key aspect of addressing the environmental sustainability of airports is the involvement of different stakeholders. As identified in figure 1 , the airport is comprised of airside and landside components. Historically, these components have been managed by distinct stakeholders. Understanding the relationship among the airport components, their respective environmental impacts, and their ways of managing stakeholder groups is critical because it leads to identifying who must act to mitigate environmental impacts. Figure 7 depicts an annotated version of the airport system boundary with suggested best practices for major airport components. Based on the literature review and the application of the SFO case study, effective sustainability practices that airports can implement in the short term are: (1) supply electricity from renewable, low-carbon sources whether on-site or from local utilities; (2) electrify transportation vehicles (e.g. shuttles, maintenance trucks) within the airport system boundary; (3) electrify all gate and ground service equipment; (4) implement water conservation practices like installation of water-efficient faucets and toilets; (5) install energy-efficient fixtures like LED lighting in all airport infrastructure; (6) select durable interior building materials for improved maintainability and reduced waste production.

Figure 7.  Suggested best practices for improving airport environmental sustainability.

These six suggested sustainability practices can result in prompt, substantive environmental benefits without significant tradeoffs. For example, relying on low-carbon electricity reduces GHG as well as other emissions. Electrifying ground service equipment and other airport vehicles results in reductions of air pollutants (NO x , PM) within the airport vicinity, which is a human health benefit. These practices are considered implementable in the 'short term' as opposed to longer-term projects such as changing the material composition of the airfield or installing on-site, decentralized wastewater treatment. These measures cover activities and operations that essentially occur at all airports, but to varying degrees of scale (e.g. all airports consume electricity). In that vein, ease of strategy implementation depends upon airport type, the resources (e.g. cost, accessibility, expertise) available to the airport for successful implementation and the controlling stakeholder. Further analysis of those distinctions is needed in future research.

One common tendency is for airports to adopt a perceived 'best practice' based upon another airport's successful implementation. But progress is needed to ensure that every airport considers all relevant environmental sustainability indicators systematically to account for regional and supply-chain effects rather than simply follow others' actions. This ties in with the further need to connect all relevant environmental impacts with local human health and ecosystem effects as communities living in proximity of airports bare a greater burden of airport operations. Future research should concentrate on the development of quantifiable indicators or performance metrics. Research and practice that increase stakeholder involvement, incorporates life-cycle assessment, and links environmental impacts with operational outcomes will help airports as well as the aviation industry to address their roles in major global challenges (e.g. climate change adaptation, mitigation of infectious diseases).

Acknowledgments

FG and JR acknowledge the financial support of the Sustainability Office at Groupe ADP.

Data availability statement

All data that support the findings of this study are included within the article (and any supplementary information files).

Supplementary material (169 kB, PDF)

Supplementary material (223 kB, PDF)

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A Systematic Review of The Impact of Commercial Aircraft Activity on Air Quality Near Airports

Karie riley.

a ICF Incorporated, L.L.C., 9300 Lee Highway, Fairfax, VA 22031-1207, U. S. A.

b U. S. EPA, Office of Transportation and Air Quality, National Vehicle and Fuel Emissions Laboratory, Ann Arbor, MI 48105, U. S. A.

Edward Carr

Bryan manning, associated data.

Commercial airport activity can adversely impact air quality in the vicinity of airports, and millions of people live close to major airports in the United States. Because of these potential impacts, a systematic literature review was conducted to identify peer reviewed literature on air quality near commercial airports and assess the quality of the studies. The systematic review included reference database searches in PubMed, Web of Science, and Google Scholar, inclusive of years 2000 through 2020. We identified 3,301 articles, and based on the inclusion and exclusion criteria developed, seventy studies were identified for extraction and evaluation using a combination of supervised machine learning and manual screening techniques. These studies consistently showed that ultrafine particulate matter (UFP) is elevated in and around airports. Furthermore, many studies show elevated levels of particulate matter under 2.5 microns in diameter (PM 2.5), black carbon, criteria pollutants, and polycyclic aromatic hydrocarbons as well. Finally, the systematic review, while not focused on health effects, identified a limited number of on-topic references reporting adverse health effects impacts, including increased rates of premature death, pre-term births, decreased lung function, oxidative DNA damage and childhood leukemia. More research is needed linking particle size distributions to specific airport activities, and proximity to airports, characterizing relationships between different pollutants, evaluating long-term impacts, and improving our understanding of health effects.

1. Introduction

A recent study by Yim et al (2015) assessed global, regional and local health impacts of civil aviation emissions, using modeling tools that address environmental impacts at different spatial scales. The study attributed approximately 16,000 premature deaths per year globally to global aviation emissions, with 87% attributable to particulate matter under 2.5 microns in diameter (PM 2.5 ). The study concludes that about a third of these mortalities are attributable to PM 2.5 exposures within 20 kilometers of an airport. While there are considerable uncertainties associated with such estimates, these results suggest that in addition to the contributions of PM 2.5 emissions to regional air quality, impacts on public health of these emissions in the vicinity of airports are an important concern. The study did not address relative contributions of specific components of PM 2.5 , such as black carbon (BC), and size fractions, such as ultrafine particulate matter (UFP), which contribute to the adverse health impacts resulting from exposure to the PM 2.5 mixture ( U. S. EPA, 2019 ).

A literature review was conducted in 2015 by the Airport Cooperative Research Program (ACRP; Kim et al., 2015 ), and focused on a wide range of peer reviewed sources, including university research as well as authoritative sources such as state agencies, the Federal Aviation Administration (FAA) and airport monitoring programs. Since the publication of the 2015 ACRP literature review, a number of studies conducted in the U. S. have been published which concluded that UFP concentrations are elevated downwind of commercial airports, and that proximity to an airport also increases particle number concentrations within residences. Particle number concentrations (PNC) are often measured as a proxy for UFP. This is because UFP is usually defined as particles with a diameter of less than 100 nanometers (nm), and most of the particle number concentration is below 100 nm. ACRP plans to update this review.

In addition to emissions from turbine engine aircraft, other sources, including piston engine aircraft, ground support equipment, and vehicle traffic all contribute to pollution levels in the vicinity of commercial airports. Turbine engine aircraft in particular emit large amounts of UFP. The UFP attributable to aircraft emissions has been associated with lung inflammation in individuals with asthma ( Habre et al., 2018 ). In addition, He et al. (2018) found that particle composition, size distribution and internalized amount of particles all contributed to promotion of reactive organic species in bronchial epithelial cells.

Airport air pollution can also disproportionately impact sensitive subpopulations. Henry et al. (2019) studied impacts of several California airports on surrounding schools and found that over 65,000 students spend 1 to 6 hours a day during the academic year being exposed to airport pollution, and the percentage of impacted students was higher for those who were economically disadvantaged. Rissman et al. (2013) studied PM 2.5 at the Hartsfield-Jackson Atlanta International Airport and found that the relationship between minority population percentages and aircraft-derived particulate matter was found to grow stronger as concentrations increased.

Although there is a significant body of research on air quality impacts in the vicinity of airports and the potential for adverse health effects from UFP, a systematic literature review of recent research on impacts of commercial airport emissions on air quality in close proximity to airports has not been conducted. Application of systematic review methods to air pollution issues was recently discussed in Lam et al. (2020) . Lam et al. point out that while a narrative review can provide a comprehensive overview of the scientific literature, a systematic review evaluates the literature in a systematic, transparent, and reproducible manner. This approach reduces the potential for bias and can help mitigate potential perception of “cherry-picking” data. Thus, we conducted a systematic review to achieve the following objectives:

• Identify peer reviewed literature on air quality near commercial airports
• Assess the quality of the studies, and
• Summarize evidence of pollutants most impacted and most likely health risks.

The focus of this systematic review was impacts of commercial airports dominated by jet aircraft activity; thus, studies that focused on ground service equipment or piston engine activity were excluded. Moreover, since this study did not focus on piston engine aircraft, emission impacts of lead due to its use as an additive in aircraft gasoline was not addressed.

2.0. Methods

The criteria used to select search terms and guide inclusion and exclusion of studies for this systematic review are presented below in Table 1 .

Inclusion/exclusion criteria.

The initial literature was conducted using reference database searches in PubMed, Web of Science, and Google Scholar. Results from these sources were deduplicated to produce a unique set of 3,287 articles. An additional 14 references were also identified from relevant articles. The reference database search began with creating sets of keywords related to emissions, airports, and measurements based on the selection criteria in Table 1 , with database-specific modifications as needed. For a citation to be included, the citation had to meet the search strategy for each keyword set. The basic limits applied for all databases included English language only and a date range of 2000 to 2020. For Web of Science, research areas were also limited to those most likely to contain relevant data. Following the literature search relevant literature was identified using the inclusion and exclusion criteria ( Table 1 ) in three screening steps: supervised clustering using text analytics, title/abstract (TiAb) screening, and full-text screening. As depicted in Figure 1 , 70 studies were ultimately selected for extraction and evaluation.

Systematic review literature flow diagram.

The first screening step, supervised clustering, was conducted using ICF International’s Document Classification and Topic Extraction Resource , DoCTER, which clusters studies that are expected to be more similar to one another using seed studies to inform automated text analysis of the titles and abstracts ( Varghese et al., 2018 ). This screening step resulted in 558 articles that were predicted as “includes” based on relevance to the search criteria. The second screening step involved manual title/abstract screening of 572 references (558 articles from the initial literature search and 14 from background search) in the program litstream tm ( Lam et al., 2020 ). Articles were tagged as “On-Topic Include”, “Supplemental Include”, or “Exclude” per the criteria in Table 1 . The screening was conducted by a single reviewer, with quality assurance review of approximately 10% of the studies by a second independent reviewer. At this step, 174 studies were tagged as on-topic “Includes”. The third screening step, also conducted in litstream tm , involved screening the full-text articles of the on-topic “Include” references from title/abstract screening. Portable document format (PDF) versions were obtained for 154 of 174 articles. On-topic references were re-classified as “On-Topic Include”, “Supplemental Include”, or “Exclude” as necessary. After full-text screening, the total number of articles classified as “On-Topic Include”, “Supplemental Include”, or “Exclude” were 102, 45, and 425, respectively.

While 102 references were tagged as “On-Topic Include” after TiAB or full-text screening, 70 U.S. and European articles were prioritized for extraction. Articles which were not extracted included those not available in PDF, some references which were more than 3 years old, and those identified from a backward search. In addition, some references which did not have PDFs to facilitate full text screening were also excluded. Extraction was conducted using litstream tm and involved recording the following information:

• Study type: Primary or Review
• Supplemental data type: Emissions, Indoor Air, Personal Monitoring, Health
• Pollutant name
• Metric: Mass concentration, Particle number concentration (PNC), Particle size distribution (PSD)
• Ambient air data type: Monitoring, Dispersion Model, Statistical/Regression Model
• Health data type: Health Effect, Intake, Risk
• Is air quality impacted?
• Is health impacted?
• Airport Name, State, Country
• Sample location: On-Airport or Off-Airport
• Contextual information: Airport Operation or Aircraft Data (presence or absence)
• Source attribution: Take-off/landing, APU, run-up, other

A list of the extracted studies is included in the supplemental information . In addition, Figure 2 provides a heatmap of studies by publication year. Articles that were extracted were also evaluated using the criteria in Table 2 to assess data reliability, relevance, and robustness. Each article was assigned an overall rating of High (n = 20), Medium (n = 37), or Low (n = 10). Review articles (n=3) were not rated. It is important to remember that when integrating the articles into an assessment for a particular purpose, the importance of each individual criterion may vary. Also, these ratings were based on level of peer review and publication in a scholarly format; however, such ratings are subjective since publication decisions can be affected by decisions other than quality of investigations ( Wells and Little, 2009 ). Furthermore, it should be noted that while we ranked studies with longer duration monitoring higher, studies that include extensive monitoring over a shorter time period can provide data with valuable insights.

Heatmap of studies by publication year.

Data quality criteria.

3.0. Results and Discussion

This systematic literature review corroborates many findings of the 2015 literature review conducted by the ACRP, in particular that UFP is highly elevated at the airport and persists downwind. Of the 70 selected studies, 33 were conducted in the U. S. These airports are listed in Table 3 . In addition, Figure 3 provides a heatmap of studies by pollutant and country. Twelve studies focused on one airport, LAX. Three were reliever rather than commercial airports (Santa Monica, Hartford, and Teterboro). Fifty of the selected studies included monitoring results, 21 included dispersion modeling, 18 included statistical analyses, and health effects were reported in 11. Furthermore, on-airport air monitoring and/or modeling was conducted for about 50% of the studies, whereas off-airport monitoring (within 20 km) and/or modeling was conducted in about 70% of the studies.

Heatmap of studies by pollutant and country.

U.S. Airports represented in this systematic review.

3.1. Ultrafine Particulate Matter

A number of early studies (2003 to 2011) found elevated UFP concentrations at fixed site monitor locations ( Westerdahl et al., 2008 ; Zhu et al., 2011 ; Hsu et al., 2013 , 2014 ; Hu et al., 2009; Choi et al., 2013 ; Klapmeyer and Marr, 2012 ). U. S. studies conducted in the last ten years showed similar results to earlier studies, although they tended to examine air quality further away from the airport using mobile monitoring or dispersion modeling ( Hudda et al, 2014 , 2016 , 2018 , 2020 ; Hudda and Fruin; 2016 ; Riley et al., 2016 ; Yu et al., 2019; Shirmohammadi et al., 2017 ). These studies focused on Los Angeles International, Hartsfield-Jackson in Atlanta, and Logan Airport in Boston. Several of these studies ( Hudda et al., 2014 ; Shirmohammadi et al., 2017 ; Hudda et al., 2020 ) showed concentrations under landing approach paths several times background concentrations. Similar results were found outside the U. S. (Stacey et al., 2020; Masiol et al., 2017; ( Keuken et al., 2015 ; Pirhadi et al.; 2020 ) Since this review, two more studies with similar findings have been published ( Austin et al., 2021 ; Ungeheuer et al., 2021 ; Zhang et al., 2020 ).

Hudda et al. (2018) investigated PNC inside and outside 16 residences in the Boston metropolitan area. They found elevated PNC within several kilometers of Boston Logan International Airport (BOS). They also found that aviation related PNC infiltrated indoors and resulted in significantly higher indoor PNC. In another study in the vicinity of Logan airport, Hudda et al. (2016) analyzed PNC impacts of aviation activities. They found that at sites 4.0 and 7.3 km from the airport, average PNCs were 2 and 1.33-fold higher, respectively, when winds were from the direction of the airport compared to other directions, indicating that aviation impacts on PNC extend many kilometers downwind of Logan airport. Furthermore, PNCs were positively correlated with flight activity after taking meteorology, time of day and week, and traffic volume into account. This correlation was not found with other pollutants. Similarly, Hudda and Fruin (2016) found that PNC was higher in areas under landing jet trajectories. Finally, they used a diffusion charging instrument to simulate alveolar lung deposition, and found a five-fold increase in deposited surface area concentration 2 to 3 kilometers downwind from the airport, decreasing to two-fold 18 km downwind. Riley et al. (2016) took extensive measurements in neighborhoods around Los Angeles International Airport and Hartsfield-Jackson International Airport in Atlanta. They found a 3 to 5-fold increase in PNCs in transects under landing approach pathways. Shirmhammadi et al. (2017) also took measurements at Los Angeles International Airport (LAX) and found PNCs were four times greater adjacent to the airport than on nearby major freeways. Stacey (2019) conducted a literature survey and concluded that the literature consistently reports PNCs close to airports are significantly higher than locations distant and upwind of airports, and that the particle size distribution is different from traditional road traffic, with more extremely fine particles. Results of a monitoring study of communities near Seattle-Tacoma International Airport was also recently released ( University of Washington, 2019 ). It also found higher levels of UFP near the airport. Furthermore, the impacted area was larger than at near roadway sites. The PM associated with aircraft landing activity was also smaller with lower black carbon concentrations than near-roadway samples.

3.2. PM 2.5 and PM 10

The majority of studies that address the criteria pollutant PM focus on PM 2.5 or smaller particles. The levels found in airport measurement studies vary, ranging from relatively low levels to those that are close to or exceeding the NAAQS. In addition, results are less consistent than for UFP.

At LAX in 2005–2006, Zhu et al. (2011) observed that daily mean PM 2.5 concentrations collected up to 600 m from the take-off runway were significantly greater ( p < 0.001) than at a background site. However, Shirmohammadi et al. (2017) observed PM 2.5 concentrations were generally lower at LAX than inside freeways within the impact zone, although, as mentioned in the introduction, particle number concentrations were greater. At Santa Monica Municipal (SMO) mobile monitoring conducted by Choi et al. (2013) in 2008 and 2011 showed comparable or lower concentrations in a residential neighborhood 120–480 m predominately downwind of SMO as compared to a neighborhood located in perpendicular wind to the airport. Similarly, Hudda et al. (2020) observed that PM 2.5 concentrations were not elevated during impact-sector winds relative to non-impact-sector winds at a residence approximately 1.3 km from BOS. Higher PM 2.5 concentrations were observed from a wind direction that indicated long-range transport of aerosols from regional sources upwind. PM 2.5 was not correlated with flight activity, suggesting PM 2.5 was primarily from sources other than aircraft. Air quality modeling studies ( Rissman et al., 2013 ; Woody et al., 2016 ) indicate higher PM 2.5 concentrations near airports. In London, however, two measurement studies at Heathrow Airport showed similar or lower concentrations at the airport than in central London (Stacey et al. 2020; Masiol et al., 2017).

3.3. Black Carbon

Studies indicate that black carbon (BC) is elevated in the vicinity of airports, as far away as 10 km. Westerdahl et al. (2008) and Zhu et al. (2011) observed elevated BC at take-off downwind of LAX. BC is emitted by a variety of combustion sources in addition to aircraft. Westerdahl et al. calculated a 12-fold increase in BC immediately downwind of the airport, although concentrations were comparable or lower than observed at nearby freeways. Zhu et al. (2011) observed that BC decreased markedly with increasing distance from the runway because of atmospheric dispersion processes, however elevated levels were still observed at 600 m downwind as compared to background. Furthermore, at Logan Airport, Hudda et al. (2020) observed that, in contrast to the PM 2.5 results discussed above, BC was 1.3-fold elevated during impact-sector winds than non-impact-sector winds at a residence sampled 1.3 km from the airport in 2017. Finally, at T.F. Green Airport, Dodson et al. (2009) developed regression models which found that aircraft activity contributed 24 to 28% of the total BC based on measurements in 2005–2006 from five sites located 0.16 to 3.7 km from the airport. However, international studies have not shown a clear association (Masiol et al., 2017; Kueken et al., 2015 , Pirhadi et al., 2020 ).

3.4. Gaseous Criteria Pollutants

In general, most on-airport studies in the U. S. showed slightly elevated concentrations of gaseous criteria pollutants, specifically carbon monoxide (CO), nitrogen dioxide (NO 2 ), and sulfur dioxide (SO 2 ), even though concentrations are often still below national ambient air quality standards. Off-airport studies had more varied results, but some studies show aviation contributions up to 12 km from the airport. Moreover, nitrogen oxides are more likely to be elevated than sulfur or carbon oxides. Ground support equipment and motor vehicles also contribute to these pollutants, especially NO 2 (as well as NO). Among the studies that address these pollutants, Hudda et al. (2020) observed at Logan airport that levels of oxides of nitrogen (NO, NO 2 , and NO x ), and CO are significantly higher (1.1 to 1.9-fold elevations) in impact sector winds than non-impact sector winds. At up to 12 km from LAX, Hudda et al. (2014) observed elevated nitrogen oxides, with similar NO 2 and particle number spatial patterns suggesting a common pollutant source. A number of other studies also showed elevated concentrations for one of more of these criteria pollutants ( Riley et al., 2016 , NO 2; Choi et al., 2013 , CO; Diez et al., 2012 , NO 2 , CO, SO 2 ). However, study results were inconclusive for some pollutants ( Choi et al., 2013 , NO; Hudda et al, 2014 , CO and SO 2 ; Adamkiewicz et al., 2010 , NO 2 ; Klapmeyer and Marr, 2012 , CO 2 and NO 2 ). International studies also showed elevated levels of pollutants for many air pollutants (Carlslaw et al., 2012; Schurmann et al., 2007 ; Yu et al., 2004 ; Valotto and Varin, 2016 ; Sidimonetti et al., 2015 ; Masiol and Harrison, 2015 ).

3.5. Hazardous Air Pollutants

Very few studies assess hazardous air pollutants (HAPs), other than polycyclic aromatic hydrocarbons (PAHs). Past speciation work indicated formaldehyde and acetaldehyde make up a large percentage of total hydrocarbons from turbine engine aircraft (12 and 4 percent respectively); while earlier work characterized PAH emissions ( U. S. EPA and U. S. FAA, 2009 ; U. S. EPA, 2009 ).

At LAX in 2003, Westerdahl et al. (2008) observed particle-phase polycyclic aromatic hydrocarbon (PM-PAH) concentrations two orders of magnitude higher at downwind location than upwind locations, although aircraft dominated areas showed lower PM-PAH than vehicular traffic areas. PM-PAH values observed at the site 500 m downwind of landings are only slightly elevated above the coastal background. In 2005, Zhu et al. (2011) reported ambient air concentrations for both particulate phase and vapor phase PAHs collected from the blast fence and at a control site. A greater amount of PAH mass was in the vapor phase than in the particle phase. The levels of vapor-phase PAH were consistently higher at the LAX blast fence than at background site. For both sites, naphthalene comprised 80 to 85% of the total vapor-phase PAH mass. The semi-volatile PAHs (from phenanthrene to chrysene) were consistently higher at the LAX blast fence than the background site, whereas, the high molecular weight PAHs (from benzo[a] pyrene to indeno[1,2,3-cd]pyrene) were lower at the blast fence than the background site.

In a residential area near SMO in California in 2008, markedly elevated concentration peaks of particle bound PAH (PB-PAH) were observed up to 600 m downwind of SMO and 250 m perpendicular to the prevailing wind directions. PB-PAH was associated with jet takeoffs but not with other aircraft operations such as idling, descents or takeoffs by reciprocal-engine aircrafts . During a freeway closure event near SMO in 2011, Choi et al. (2013) observed highly elevated PB-PAH ambient air concentration which were likely explained by jet take-offs. At a residential site 1.3 km from BOS, observed significantly higher PB-PAH concentrations in impact sector wind than non-impact-sector wind.

3.6. Health Effects

This systematic review only identified a limited number of on-topic references with health effects, impact or risk data ( Figure 4 ). While this literature review was not intended to capture all relevant health effect studies, having focused on ambient air data, we summarize here the studies that were identified using our search parameters. Additionally, the systematic review focused on peer-reviewed articles from databases, rather than government or airport studies which may be more likely address public health issues. Potential endpoints identified in this literature review are as follows:

Heatmap of studies by type of health data.

• Yim et al. (2015) assessed global, regional and local health impacts of civil aviation emissions, using modeling tools that address environmental impacts at different spatial scales. The study attributed approximately 16,000 premature deaths per year globally to global aviation emissions, with 87% attributable to PM 2.5 . The study concludes that about a third of these mortalities are attributable to PM 2.5 exposures within 20 kilometers of an airport.
• Wing et al. (2020) evaluated whether UFPs from jet aircraft emissions are associated with increased rates of pre-term birth among pregnant mothers living within 15 km downwind of LAX. The study, consisted of 147,186 mothers who gave birth between 2008 a and 2016. The study concludes that aircraft emissions play an etiologic role, independent of noise and traffic-related pollution. Specifically, the odds ratio (OR) per interquartile range (IQR) increase relative to UFP exposure was 1.04.
• Lammers et al. (2020) investigated respiratory and cardiopulmonary outcomes in 21 healthy adults who were repeatedly exposed to ambient air in a mobile laboratory set up 300 m from the runway at Amsterdam Schipol Airport (2 to 5 visits, 5 hours each). Total PNC was significantly associated with decreased lung function, primarily a decrease in forced vital capacity (FVC) and prolonged corrected QT (duration of ventricular repolarization corrected for heart rate). The authors observed small effects after only a single 5 hr exposure. These effects were mainly associated with particles < 20 nm.
• At LAX, Hudda and Fruin (2016) measured alveolar lung deposited surface area (ALDSA), which is the fraction of lung deposited surface area (LDSA) deposited in the alveolar region of the lung. The particle number concentration increases in the areas impacted by LAX are accompanied by pronounced decreases in particle size and increases in ALDSA concentration.
• Using ambient PM 0.25 collected adjacent and downwind from LAX in 2016 as well as PM directly sampled from diluted exhaust of turbine and diesel engines, He et al. (2018) demonstrated adverse responses in human bronchial epithelial (16HBE) cells, specifically effects on cell viability/cytotoxicity, ROS activity and inflammatory mediators release. The paper suggested that elemental composition and oxidative potential of the PM samples seem to explain these biological responses.
• Cavallo et al. (2006) characterized the exposure to several polyaromatic hydrocarbons (PAHs) and evaluated the genotoxic and oxidative effects in airport personnel (n=14) at Da Vinci airport in Rome, Italy. Air sample were collected at the airport apron, building, and terminal/office areas. Urine and blood samples were collected from exposed individuals (those that work in close proximity to the airport) and control individuals (those that work in the administrative offices of the airport). Genotoxic effects and early direct-oxidative DNA damage were evaluated by micronucleus and formamidopyrimidine DNA glycosylase (Fpg) modified comet assay ( Shukla et al., 2011 ) on lymphocytes and exfoliated buccal cells, and by chromosomal aberrations and sister chromatid exchange analyses. Urinary OH-pyrene did not show differences between exposed and controls, although the controls may have low daily exposure to PAH. The results found an induction of sister chromatid exchange due to PAH exposure and an increase of total chromosomal aberrations. Senkayi, et al. (2014) evaluated whether there is an association between childhood leukemia cases and airport emissions in Texas over a 10-year period. The work concluded that an association exists based on 1) comparison of distance to airports with incidence ratios in census blocks, and 2) regression model to predict childhood leukemia incidences based on benzene emissions from various sources.

Recently, a systematic review of health effects associated with exposure to jet engine emissions in the vicinity of airports was published ( Bendtsen et al., 2021 ). This study concluded that literature on health effects was sparse but jet engine emissions have physicochemical properties similar to diesel exhaust particles, and that exposure to jet engine emissions is associated with similar adverse health effects as exposure to diesel exhaust particles and other traffic emissions.

3.7. Data Strengths and Limitations

The papers identified in these studies consistently showed UFP is elevated in and around airports. The most recent studies have heavily focused on UFP and addressed gradients with increasing distance from airports. Furthermore, most of the studies addressed contributions from background and freeways, and at least qualitatively characterized airport and aircraft data with respect to air quality.

However, a lack of standard methods and instrumentation make comparisons of measured concentrations among studies difficult. In addition, there are very few long-term studies. Finally, only a few airports have been studied, making it difficult to provide broad generalizations when differences in airport and aircraft operations, geography, and meteorology have a significant impact on the results.

3.8. Recommendations for Future Work

This literature review underscores the need for research in a number of key areas:

• Characterization of ambient particle size distribution from specific aircraft activities (i.e., take-off and landing). While research shows the near airport environment is a hotspot for PM 2.5 and UFP, particle size distributions may vary spatially within that environment depending on where different types of activity occur. This spatial distribution (i.e. take-off and landing) needs to be better characterized.
• Investigation of particle size distribution changes with increasing distance from the airport.
• Attribution of concentrations to individual source types. For example, roadway traffic emissions from nearby freeways may make a significant contribution to ambient concentrations in the vicinity of airports.
• Assessment of the relationship between UFP and other pollutants, especially HAPs.
• Improvement of the understanding of the health effects and impacts of pollutants and disparate impacts on minority or disadvantaged communities as well as children.
• Conducting long-term studies to capture variation in ambient concentrations across years and seasons.
• Conducting studies at more airports to capture differences in airport source types (e.g., aircraft fleet mixes), source operations, airport layout and location, surrounding geography, and meteorology.

Supplementary Material

Supplemental.

Publisher's Disclaimer: Disclaimer

The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the U. S. Environmental Protection Agency.

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Airport operations management

• Published: 31 August 2019
• Volume 41 , pages 613–614, ( 2019 )

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• Han Hoogeveen 2 &
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The airline industry is important for the global economy. Airports, in particular hub airports, are the backbone of air transportation. Operations in the terminal and at the airfield as well as the runways need to be planned in an efficient way. This special issue is dedicated to operations research methods supporting airport operations management. Large airports require a diversity of tasks to be performed and problems to be solved. Amongst them are resource allocation problems (e.g. gates/stands, check-in desks, baggage station or carousels); sequencing or scheduling problems (e.g. runway sequencing); timetabling and rostering problems (e.g. check-in or security staff); or routing problems (e.g. for aircraft). But many other problems can also be found in airports, such as facility location or passenger flow prediction and optimisation. Airports are key for the air transportation system, and inefficiencies there can have knock-on effects throughout the air transportation system, delaying flights and potentially increasing pollutant emissions as well as costs.

Modern research trends are moving beyond the traditional static individual problems, considering multi-objective problems and trade-offs (e.g. fuel vs. cost vs. time), combined problems (e.g. runway sequencing and trajectory optimisation), dynamic and stochastic problems, creating more robust solutions, or considering some of the complex real-world constraints which can cause problems for the elegant solutions we may prefer. Perhaps unsurprisingly, this focus was observed in the research papers submitted for this special issue. From the 21 papers submitted to this special issue, the following three papers have been selected. All three contributions base their analysis on real-world data:

Dijk et al. ( 2019 ) consider the Tactical Stand Allocation problem (also known as the Gate Assignment problem) as it occurs at the Guarulhos International Airport of Sao Paulo. The quality of such a plan is judged on the basis of four conflicting objectives, one of which is maximising revenues. Moreover, the solutions must be robust to deal with deviations in the arrival and departure times. To solve this problem, the authors apply a variant of recoverable robustness to find a solution that can be made feasible for a set of scenarios generated on the basis of historical data.

Samà et al. ( 2019 ) consider a combined trajectory management and sequencing problem for aircraft landing and taking-off from an airport, aiming to improve a variety of performance indicators, illustrating the trade-offs within this combined problem, and considering the benefits of three different approaches to combining the problems. Computational experiments are performed on real-world data from Milano Malpensa airport.

Yalcin et al. ( 2019 ) analyse a grid-based storage system. They devise efficient algorithms to store new items or to retrieve stored items, where currently stored items can be pushed into other cells in the grid. Several variants of these strategies are tested in a simulation environment, which results are to be used to design a baggage storage system at Frankfurt Airport.

Our sincere thanks go to all of the authors and reviewers for contributing to this special issue.

Dijk B, Santos BF, Pita JP (2019) The recoverable robust stand allocation problem: a GRU airport case study. OR Spectr. https://doi.org/10.1007/s00291-018-0525-3

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Samà M, D’Ariano A, Palagachev K, Gerdts M (2019) Integration methods for aircraft scheduling and trajectory optimization at a busy terminal manoeuvring area. OR Spectr. https://doi.org/10.1007/s00291-019-00560-1

Yalcin A, Koberstein A, Schocke K-O (2019) Motion and layout planning in a grid-based early baggage storage system. OR Spectr. https://doi.org/10.1007/s00291-018-0545-z

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Airport Research Needs: Cooperative Solutions -- Special Report 272 (2003)

Chapter: 5 conclusions and recommendations, 5 conclusions and recommendations.

T he key findings of this report are summarized in this chapter. The committee believes that the findings

Justify the creation of a national research program focused on the needs of airport operators;

Reveal how such a program can play a role in helping airport operators meet the many demands of federal agencies, state governments, local communities, and airport users; and

Provide guidance on governing, funding, and administering an airport research program.

JUSTIFICATION FOR A RESEARCH PROGRAM FOCUSED ON AIRPORTS

Some 5,000 airports scattered across the country are open to public use in the United States, including more than 500 that offer airline service. They vary in size from more than 50 square miles to a few dozen acres and accommodate aircraft ranging from 500-seat jet airliners to single-engine props. They form a key component of the country’s heavily used aviation system. Unlike the centralized air traffic control enterprise, which is run almost entirely by the federal government, the nation’s airports are a collection of independent entities owned and operated by thousands of mostly public agencies.

The diversity and decentralization of the airport system are strengths. Competition among airports for the business of airlines and other aircraft users prompts efficiencies and innovations in products, processes, and services. At the same time, individual airports are elements of regional and national transportation networks; they are interconnected and dependent on one another. For aviation users—whether airline passengers, shippers, or general aviation (GA) operators—the vast airport network with its many origin and destination points is what makes the nation’s aviation system so useful.

Recognizing the importance of building and maintaining a nationally integrated aviation system, the federal government has long played an important role in providing assistance to thousands of airports run by state and local governments. During the past three decades, it has granted more than $30 billion to operators for improvements in runways and taxiways, terminal facilities, noise mitigation, safety equipment, security, and air navigation and guidance systems. Most of the revenues to fund these investments stem from federal taxes and other levies on aviation users maintained in the Airport and Airway Trust Fund.

To protect the large federal investment in the nation’s airport infrastructure and ensure its safe and efficient use, the Federal Aviation Administration (FAA) has established various standards governing major aspects of the design, construction, maintenance, and operations of airport facilities. In supporting the development and implementation of these standards, FAA sponsors research on topics ranging from pavement durability to noise modeling and mitigation.

Yet, from the standpoint of airport operators, different research needs are apparent. For example, an increase in an airport’s operations must be carried out without significantly increasing noise, air pollution, or other environmental impacts. Security must be strengthened without unduly burdening and possibly driving away users. Federal restrictions on how airports can generate revenues from landing fees and other user charges—restrictions that accompany most federal grants—must be balanced against demands by state and municipal owners that airports seek out new revenue sources to become self-supporting. In the end, it is up to the airport operators themselves to find ways to meet these many demands.

Operators face a growing challenge in responding to these demands. New agencies with jurisdiction over airports, such as the Transportation Security Administration, are imposing new requirements. Others, such as the U.S. Environmental Protection Agency and its state counterparts, have gradually expanded their authority into the realm of airport planning, construction, and operations. Thus, what may appear to be straightforward requirements from the perspective of a single agency can result in many uncertainties and problems for airport operators. At the moment, operators do not have a research capability to address these uncertainties and solve the resulting problems.

The airport research enterprise does not currently provide a means for operators to cooperate among themselves and with other interested parties to

find solutions to shared problems or to seek new ideas to improve airport operations. The federal government has much at stake in ensuring that such research is undertaken and that it is of the highest quality. Airports with fewer problems are more likely to use their resources efficiently and to require less federal assistance. They are more likely to be able to respond effectively to the requirements of federal agencies—whether to strengthen security, protect the environment, or increase capacity. And they are more likely to be able to meet the demands of airport users, which will ultimately benefit travelers and shippers depending on safe, secure, and efficient air service.

Cooperative research activities confer many other benefits that can be difficult to gauge. The National Highway Cooperative Research Program (NCHRP) and the Transit Cooperative Research Program (TCRP) have demonstrated that regular collaboration of practitioners, public officials, researchers, and technical experts can provide opportunities for the exchange of information and ideas. Moreover, practitioners who are actively involved in research gain skills and expertise that strengthen the industry’s professional capacity and help attract talented individuals to the field. Of course, research performed at universities is essential for training students and interesting them in the airport management and engineering professions.

UNIQUE ROLE OF AN AIRPORT COOPERATIVE RESEARCH PROGRAM

The mission of a national airport cooperative research program (ACRP) must be clear and well articulated so that the program complements, and does not duplicate or detract from, existing research activities. An ACRP, unlike any current program, will provide an opportunity to address problems that

Many operators share but that tend to be too costly or complex for a single operator or a small group of operators to research;

Receive limited attention because of a lack of funding or incompatibility with the mission and institutional requirements of federal agencies and others that traditionally perform airport-related research; and

Can be researched with a reasonable expenditure of time and effort to yield results that can be readily implemented by airport operators and users.

The following are examples of airport needs in several common problem areas. They illustrate the kinds of research questions that could be addressed through a national ACRP.

Operations and safety

What is a safe and efficient speed for escalators and moving sidewalks in airport environments that are often crowded with hurrying passengers carrying luggage?

How are proposed changes in air traffic control and area navigation rules, such as terminal instrument procedures, likely to affect the configuration, placement, and capacity of airport taxiways and runways? What effects are these changes likely to have on overall airport capacity?

Maintenance

What methods are most suitable for choosing among alternative maintenance products and practices for use under different airport conditions?

What tools do operators have—and how effective are they—for monitoring the condition of assets, prioritizing maintenance activity, and managing maintenance personnel and contractors?

Design of infrastructure and equipment

How do airports currently use FAA’s advisory circulars? Which circulars are most urgently in need of updating to give airports better design guidance?

To what extent have changes in the dimensions, controllability, and visibility of modern aircraft been accounted for in FAA design standards for taxiway geometrics, signage visibility, and wingtip clearances, and what modifications of these standards are warranted?

Finance and administration

What experience do airport operators have in this country and abroad in using design–build–finance techniques for expediting construction of new facilities? What have been the positive and negative results of these efforts? What can be learned from experiences in public works and other modes of transportation?

What are the emerging challenges that airports face, in light of heightened security concerns, in recruiting and retaining qualified personnel and reducing workplace stress? What can be learned from the practices of other industries facing similar challenges?

What changes in aircraft types, dimensions, and uses can be expected in the medium and near terms, and how can these changes be accommodated in capital planning for airport facilities?

What changes in demand-forecasting methodologies are needed to better assess future facility requirements given the uncertainties now affecting the entire commercial aviation sector?

Environment

What alternative aircraft deicing methods and materials are available? How well do they balance the needs for safety assurance, environmental protection, affordability, and compatibility with operational requirements?

What are the data and modeling requirements to analyze emissions of air toxics associated with health risks at airports in a manner that is scientifically credible and useful in decision making?

What changes in the current regulatory framework for airports would be required to streamline the planning and environmental documentation process for critically needed airport improvements?

What cost-effective changes in terminal designs and features (e.g., “way-finding” signs) are available to facilitate security processing, avoid crowding, and expedite the movement of passenger traffic through terminals?

How can passenger and baggage flows be modeled accurately to assist in the longer-term infrastructure planning for the design and location of explosive detection systems and for deployment of security personnel?

Although this list is not comprehensive, it reveals a diversity of research needs. Specific research interests will undoubtedly vary by airport size, location, use patterns, and other factors. Operators of GA airports, for instance, may be more interested in research on the kinds of asphalt pavements found on short-field runways than on the more rigid concrete structures used for paving runways that can handle large commercial jets. Likewise, northern airports will have a greater interest in research on snow- and ice-control methods and materials, while commercial-service airports will be the most interested in research to improve the efficiency of passenger and cargo flows.

The wide scope of research needs suggests that a cooperative research program must be responsive, rigorous, objective, and capable of involving practitioners and researchers with expertise from many disciplines. Insights gained from reviewing the experiences of NCHRP and TCRP indicate that how a program is governed, financed, and managed will have a large bearing on these capabilities.

PROGRAM GOVERNANCE, FINANCE, AND MANAGEMENT: LESSONS FROM NCHRP AND TCRP

A research program’s overall design and organizational characteristics have a fundamental influence on the research needs addressed, how the research is carried out, the quality of the results, and the extent to which the results are applied. The committee’s review of NCHRP and TCRP suggests that the following characteristics will be especially important in guiding the establishment of an airport research program.

Airport operators must integrate the demands of multiple federal agencies, state and local governments, and airport users. The challenges and problems they face result in research needs and priorities that differ from those making the demands. Operators, therefore, must have a primary role in setting the research agenda, defining the expected products of research, and ensuring the timeliness and applicability of the research results. In doing so, they must cooperate closely with the federal agencies and users of airports, all of whom have an interest in ensuring that the operators succeed.

The experiences of NCHRP and TCRP suggest that an ACRP will require a strong and committed governing board. The board should consist of top executives from a cross section of the nation’s airports as well as representatives from federal agencies, industry organizations, and airport users. The governing board must define the research priorities and ensure overall quality and relevance of the research. It must articulate expected research products and assist with dissemination of research results. Finally, it must coordinate with other research programs that have complementary functions.

The federal government, the private sector, and airport operators collectively spend hundreds of millions of dollars each year on airport-related research and technology development. The committee did not examine whether these funds are allocated appropriately or have been successful in achieving their objectives. However, the study indicates that airports do not currently have a way to fund urgent, short-term research to meet their needs. While the immediate and near-term problems of airport operators are not intrinsically more important than those being addressed by established research programs, they differ in nature and urgency, and thus they deserve explicit attention.

The experiences of NCHRP and TCRP suggest the importance of having finances dedicated to cooperative research. Dedicated funding can provide a base that is sufficiently large to address a range of research needs and reliable enough to sustain interest in the program. A program that is limited to a narrow set of research problems because of limited finances is likely to become marginalized. Airport operators in particular must view the program as a dependable source of ideas and information. They must have a sense of ownership of the program—a commitment to ensuring that the program addresses airport needs and is run efficiently. Because the ultimate beneficiaries of the research will be airport users, financing of the program through aviation user fees can provide these critical stakeholder connections.

NCHRP and TCRP are managed by TRB. Their experience demonstrates that the organization managing the research program must provide more than accounting and administrative services. It must refine the research needs, establish objective means of selecting competent researchers, ensure that research results are technically sound, and disseminate the results widely within the appropriate communities. It must have experience in managing a research program covering a number of disciplines.

Both NCHRP and TCRP use competitively selected contractors to perform the work. Contract-based research offers the greatest flexibility in utilizing the varied expertise and facilities needed for a diverse research portfolio. It also requires competent managers to develop requests for proposals, screen competing researchers with regard to their qualifications, and administer the contracts. The managers must be able to draw on both technical experts and practitioners to define projects, participate in merit review to select capable researchers to perform the work, and peer-review the quality and applicability of the results. Above all, the management organization must be viewed as impartial, independent, and committed to undertaking quality research and disseminating the results.

MODEL ACRP AND NEXT STEPS

Congress requested this study of the desirability of a national cooperative research program for airports. In so doing, it asked for an assessment of the applicability of the financing and administrative approaches used by NCHRP and TCRP. The committee believes that these programs offer an organizational

model well suited to meeting the research needs of airport operators and proposed means of governing, financing, and managing an ACRP in Chapter 4 . A proposal for a trial program is outlined in Box 5-1 . It embodies the key characteristics discussed above:

The program would be governed and guided by the top managers from a cross section of the nation’s airports in collaboration with representatives of federal agencies, airport users, and others.

It would be financed with revenues derived from aviation users. Such financing would bring about a research agenda that is focused on producing solutions with direct application to airport problems and would thus prompt a strong commitment to the program on the part of the airport and aviation communities.

Its management would be structured to ensure that the research products meet the highest applicable standards and are accessible to users.

This model is derived from the NCHRP and TCRP structures. It provides a first step toward creating an ACRP. The experience of TCRP—established only a decade ago—provides insights into subsequent steps. Convinced of the merits of a cooperative research program, transit agencies took it upon themselves to broaden awareness and build consensus for a cooperative research program. They acted through industry associations to clarify the organizational structure of the desired program, outline a legislative proposal, and mobilize support for it. Top transit managers have remained active in the program since its inception. The nation’s airport operators will need to commit themselves to a similar effort.

TRB Special Report 272 - Airport Research Needs: Cooperative Solutions urges the U.S. Congress to establish a national airport cooperative research program. The committee that produced the report called such a program essential to ensuring airport security, efficiency, safety, and environmental compatibility.

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This Airport Was Just Named the Most Luxurious in the U.S.

The research even accounts for if an airport has a caviar bar.

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As any frequent traveler can tell you, flying can sometimes be a drag. Not the cruising comfortably at 35,000 feet part, but the getting through the airport part. Nightmarish parking, a lengthy line at check-in, the never-pleasant security line, and the search for your gate can all add up to an unpleasant experience before you even get to board. While we can't do anything about the airports that are due for a serious upgrade, we can at least point you to the airports that not only enhance the travel experience but make it. 

In February, All Clear Travel Insurance unveiled the findings of its research searching for the most luxurious airports in the world. To determine its rankings, the insurance service analyzed more than 1,800 airports, evaluating them on how many had a significant selection of passenger lounges available (minimum 10) via data by Loungebuddy, how many designer shops it has, and how many 4- and 5-star hotels are located nearby.

Each airport was also given a score on whether travelers could find a Champagne bar or caviar house too, because, you know, we all need that. After looking at all the airports the team shortlisted 69 and named New York City's John F. Kennedy International Airport (JFK) as the most luxurious airport in the United States.

JFK ranked as the 11th most luxurious airport overall, scoring high marks for its high number of lounges (22) and for the high number of luxury stores across its terminals (16). However, it lost points because it lacks any high-end hotels nearby, giving it a total luxury score of 48 out of 100. This pales in comparison to the No. 1 pick, Dubai International Airport (DXB), which scored 83 out of 100. 

Coming in a close second is the United Kingdom's Heathrow Airport (LHR), located in London with a score of 82 out of 100. Also in the top 5 are Hamad International Airport (DOH) in Qatar, Paris Charles de Gaulle Airport (CDG) in France, and Sydney International Airport (SYD) in Australia. The only other U.S. airport to make the top 20 is California's Los Angeles International Airport (LAX) at No. 16.

See all the other airports to make the top 20 list at allcleartravel.co.uk . 

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Title: realm: reference resolution as language modeling.

Abstract: Reference resolution is an important problem, one that is essential to understand and successfully handle context of different kinds. This context includes both previous turns and context that pertains to non-conversational entities, such as entities on the user's screen or those running in the background. While LLMs have been shown to be extremely powerful for a variety of tasks, their use in reference resolution, particularly for non-conversational entities, remains underutilized. This paper demonstrates how LLMs can be used to create an extremely effective system to resolve references of various types, by showing how reference resolution can be converted into a language modeling problem, despite involving forms of entities like those on screen that are not traditionally conducive to being reduced to a text-only modality. We demonstrate large improvements over an existing system with similar functionality across different types of references, with our smallest model obtaining absolute gains of over 5% for on-screen references. We also benchmark against GPT-3.5 and GPT-4, with our smallest model achieving performance comparable to that of GPT-4, and our larger models substantially outperforming it.

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Heathrow urges government to scrap £10 fee for transit passengers

London hub says charge for overseas travellers using UK airports puts country at competitive disadvantage

Heathrow has called on the government to scrap a new £10 charge for overseas travellers using UK airports to connect to other flights, warning that it puts UK airports at a competitive disadvantage compared with other European rivals.

The government introduced the Electronic Travel Authorisation (ETA) in November for Qatari nationals travelling to the UK from Qatar, with a wider rollout for other countries throughout 2024.

The ETA is largely based on the US Electronic System for Travel Authorization (Esta) system, and requires travellers to apply to enter the country before departing and pay a £10 fee.

This applies not only to direct flights from the country but also for those who are using UK airports for more than two hours to connect to other flights.

Heathrow said while it supported the overall rationale behind the ETA, transiting passengers needed to be exempted as this was hitting passenger numbers.

The airport pointed to the impact it had on travellers from Qatar – it said there had been 19,000 fewer transit passengers coming through the airport in the first four months of ETA rules applying. It added that each month recorded the lowest proportion of transiting passengers from the country for 10 years.

The update said: “This is a huge blow to UK competitiveness as many long-haul routes, which are highly important to the UK’s economy, exports and wider connectivity, rely on transit passengers. With more connecting passengers expected to choose other hubs as the scheme expands, minsters need to take action to remove this measure.”

Heathrow recorded its busiest Easter weekend this year, with 936,000 passengers using the airport across the bank holiday period. This contributed to 7 million people travelling through the London hub in March, the highest ever for that month.

The chief executive, Thomas Woldbye, said: “The government needs to exempt airside transit passengers from the ETA scheme to avoid encouraging passengers to spend and do business elsewhere. We need to level the playing field, so the UK aviation industry continues to be world class.”

A Home Office spokesperson said: “We are introducing an electronic travel authorisation scheme to enhance border security by increasing our knowledge about those seeking to come to the UK and preventing the arrival of those who pose a threat.

“Requiring transit passengers to obtain an ETA stops people who may use connecting flights to avoid gaining permission to travel to the UK. We are keeping this under review as we continue to roll out the scheme.”

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About 1 in 4 u.s. teachers say their school went into a gun-related lockdown in the last school year.

Twenty-five years after the mass shooting at Columbine High School in Colorado , a majority of public K-12 teachers (59%) say they are at least somewhat worried about the possibility of a shooting ever happening at their school. This includes 18% who say they’re extremely or very worried, according to a new Pew Research Center survey.

Pew Research Center conducted this analysis to better understand public K-12 teachers’ views on school shootings, how prepared they feel for a potential active shooter, and how they feel about policies that could help prevent future shootings.

To do this, we surveyed 2,531 U.S. public K-12 teachers from Oct. 17 to Nov. 14, 2023. The teachers are members of RAND’s American Teacher Panel, a nationally representative panel of public school K-12 teachers recruited through MDR Education. Survey data is weighted to state and national teacher characteristics to account for differences in sampling and response to ensure they are representative of the target population.

We also used data from our 2022 survey of U.S. parents. For that project, we surveyed 3,757 U.S. parents with at least one child younger than 18 from Sept. 20 to Oct. 2, 2022. Find more details about the survey of parents here .

Here are the questions used for this analysis , along with responses, and the survey methodology .

Another 31% of teachers say they are not too worried about a shooting occurring at their school. Only 7% of teachers say they are not at all worried.

This survey comes at a time when school shootings are at a record high (82 in 2023) and gun safety continues to be a topic in 2024 election campaigns .

Teachers’ experiences with lockdowns

About a quarter of teachers (23%) say they experienced a lockdown in the 2022-23 school year because of a gun or suspicion of a gun at their school. Some 15% say this happened once during the year, and 8% say this happened more than once.

High school teachers are most likely to report experiencing these lockdowns: 34% say their school went on at least one gun-related lockdown in the last school year. This compares with 22% of middle school teachers and 16% of elementary school teachers.

Teachers in urban schools are also more likely to say that their school had a gun-related lockdown. About a third of these teachers (31%) say this, compared with 19% of teachers in suburban schools and 20% in rural schools.

Do teachers feel their school has prepared them for an active shooter?

About four-in-ten teachers (39%) say their school has done a fair or poor job providing them with the training and resources they need to deal with a potential active shooter.

A smaller share (30%) give their school an excellent or very good rating, and another 30% say their school has done a good job preparing them.

Teachers in urban schools are the least likely to say their school has done an excellent or very good job preparing them for a potential active shooter. About one-in-five (21%) say this, compared with 32% of teachers in suburban schools and 35% in rural schools.

Teachers who have police officers or armed security stationed in their school are more likely than those who don’t to say their school has done an excellent or very good job preparing them for a potential active shooter (36% vs. 22%).

Overall, 56% of teachers say they have police officers or armed security stationed at their school. Majorities in rural schools (64%) and suburban schools (56%) say this, compared with 48% in urban schools.

Only 3% of teachers say teachers and administrators at their school are allowed to carry guns in school. This is slightly more common in school districts where a majority of voters cast ballots for Donald Trump in 2020 than in school districts where a majority of voters cast ballots for Joe Biden (5% vs. 1%).

What strategies do teachers think could help prevent school shootings?

The survey also asked teachers how effective some measures would be at preventing school shootings.

Most teachers (69%) say improving mental health screening and treatment for children and adults would be extremely or very effective.

About half (49%) say having police officers or armed security in schools would be highly effective, while 33% say the same about metal detectors in schools.

Just 13% say allowing teachers and school administrators to carry guns in schools would be extremely or very effective at preventing school shootings. Seven-in-ten teachers say this would be not too or not at all effective.

How teachers’ views differ by party

Republican and Republican-leaning teachers are more likely than Democratic and Democratic-leaning teachers to say each of the following would be highly effective:

• Having police officers or armed security in schools (69% vs. 37%)
• Having metal detectors in schools (43% vs. 27%)
• Allowing teachers and school administrators to carry guns in schools (28% vs. 3%)

And while majorities in both parties say improving mental health screening and treatment would be highly effective at preventing school shootings, Democratic teachers are more likely than Republican teachers to say this (73% vs. 66%).

Parents’ views on school shootings and prevention strategies

In fall 2022, we asked parents a similar set of questions about school shootings.

Roughly a third of parents with K-12 students (32%) said they were extremely or very worried about a shooting ever happening at their child’s school. An additional 37% said they were somewhat worried.

As is the case among teachers, improving mental health screening and treatment was the only strategy most parents (63%) said would be extremely or very effective at preventing school shootings. And allowing teachers and school administrators to carry guns in schools was seen as the least effective – in fact, half of parents said this would be not too or not at all effective. This question was asked of all parents with a child younger than 18, regardless of whether they have a child in K-12 schools.

Like teachers, parents’ views on strategies for preventing school shootings differed by party. 

Note: Here are the questions used for this analysis , along with responses, and the survey methodology .

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About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of The Pew Charitable Trusts .

Prestigious cancer research institute has retracted 7 studies amid controversy over errors

Seven studies from researchers at the prestigious Dana-Farber Cancer Institute have been retracted over the last two months after a scientist blogger alleged that images used in them had been manipulated or duplicated.

The retractions are the latest development in a monthslong controversy around research at the Boston-based institute, which is a teaching affiliate of Harvard Medical School. 

The issue came to light after Sholto David, a microbiologist and volunteer science sleuth based in Wales, published a scathing post on his blog in January, alleging errors and manipulations of images across dozens of papers produced primarily by Dana-Farber researchers . The institute acknowledged errors and subsequently announced that it had requested six studies to be retracted and asked for corrections in 31 more papers. Dana-Farber also said, however, that a review process for errors had been underway before David’s post. 

Now, at least one more study has been retracted than Dana-Farber initially indicated, and David said he has discovered an additional 30 studies from authors affiliated with the institute that he believes contain errors or image manipulations and therefore deserve scrutiny.

The episode has imperiled the reputation of a major cancer research institute and raised questions about one high-profile researcher there, Kenneth Anderson, who is a senior author on six of the seven retracted studies. 

Anderson is a professor of medicine at Harvard Medical School and the director of the Jerome Lipper Multiple Myeloma Center at Dana-Farber. He did not respond to multiple emails or voicemails requesting comment. 

The retractions and new allegations add to a larger, ongoing debate in science about how to protect scientific integrity and reduce the incentives that could lead to misconduct or unintentional mistakes in research. 

The Dana-Farber Cancer Institute has moved relatively swiftly to seek retractions and corrections. 

“Dana-Farber is deeply committed to a culture of accountability and integrity, and as an academic research and clinical care organization we also prioritize transparency,” Dr. Barrett Rollins, the institute’s integrity research officer, said in a statement. “However, we are bound by federal regulations that apply to all academic medical centers funded by the National Institutes of Health among other federal agencies. Therefore, we cannot share details of internal review processes and will not comment on personnel issues.”

The retracted studies were originally published in two journals: One in the Journal of Immunology and six in Cancer Research. Six of the seven focused on multiple myeloma, a form of cancer that develops in plasma cells. Retraction notices indicate that Anderson agreed to the retractions of the papers he authored.

Elisabeth Bik, a microbiologist and longtime image sleuth, reviewed several of the papers’ retraction statements and scientific images for NBC News and said the errors were serious. 

“The ones I’m looking at all have duplicated elements in the photos, where the photo itself has been manipulated,” she said, adding that these elements were “signs of misconduct.” 

Dr.  John Chute, who directs the division of hematology and cellular therapy at Cedars-Sinai Medical Center and has contributed to studies about multiple myeloma, said the papers were produced by pioneers in the field, including Anderson. 

“These are people I admire and respect,” he said. “Those were all high-impact papers, meaning they’re highly read and highly cited. By definition, they have had a broad impact on the field.” 

Chute said he did not know the authors personally but had followed their work for a long time.

“Those investigators are some of the leading people in the field of myeloma research and they have paved the way in terms of understanding our biology of the disease,” he said. “The papers they publish lead to all kinds of additional work in that direction. People follow those leads and industry pays attention to that stuff and drug development follows.”

The retractions offer additional evidence for what some science sleuths have been saying for years: The more you look for errors or image manipulation, the more you might find, even at the top levels of science. 

Scientific images in papers are typically used to present evidence of an experiment’s results. Commonly, they show cells or mice; other types of images show key findings like western blots — a laboratory method that identifies proteins — or bands of separated DNA molecules in gels. 

Science sleuths sometimes examine these images for irregular patterns that could indicate errors, duplications or manipulations. Some artificial intelligence companies are training computers to spot these kinds of problems, as well. 

Duplicated images could be a sign of sloppy lab work or data practices. Manipulated images — in which a researcher has modified an image heavily with photo editing tools — could indicate that images have been exaggerated, enhanced or altered in an unethical way that could change how other scientists interpret a study’s findings or scientific meaning. 

Top scientists at big research institutions often run sprawling laboratories with lots of junior scientists. Critics of science research and publishing systems allege that a lack of opportunities for young scientists, limited oversight and pressure to publish splashy papers that can advance careers could incentivize misconduct. 

These critics, along with many science sleuths, allege that errors or sloppiness are too common , that research organizations and authors often ignore concerns when they’re identified, and that the path from complaint to correction is sluggish. 

“When you look at the amount of retractions and poor peer review in research today, the question is, what has happened to the quality standards we used to think existed in research?” said Nick Steneck, an emeritus professor at the University of Michigan and an expert on science integrity.

David told NBC News that he had shared some, but not all, of his concerns about additional image issues with Dana-Farber. He added that he had not identified any problems in four of the seven studies that have been retracted. 

“It’s good they’ve picked up stuff that wasn’t in the list,” he said. 

NBC News requested an updated tally of retractions and corrections, but Ellen Berlin, a spokeswoman for Dana-Farber, declined to provide a new list. She said that the numbers could shift and that the institute did not have control over the form, format or timing of corrections. 

“Any tally we give you today might be different tomorrow and will likely be different a week from now or a month from now,” Berlin said. “The point of sharing numbers with the public weeks ago was to make clear to the public that Dana-Farber had taken swift and decisive action with regard to the articles for which a Dana-Farber faculty member was primary author.” 

She added that Dana-Farber was encouraging journals to correct the scientific record as promptly as possible. 

Bik said it was unusual to see a highly regarded U.S. institution have multiple papers retracted. 

“I don’t think I’ve seen many of those,” she said. “In this case, there was a lot of public attention to it and it seems like they’re responding very quickly. It’s unusual, but how it should be.”

Evan Bush is a science reporter for NBC News. He can be reached at [email protected].

Francis Collins: Why I’m going public with my prostate cancer diagnosis

I served medical research. now it’s serving me. and i don’t want to waste time..

Over my 40 years as a physician-scientist, I’ve had the privilege of advising many patients facing serious medical diagnoses. I’ve seen them go through the excruciating experience of waiting for the results of a critical blood test, biopsy or scan that could dramatically affect their future hopes and dreams.

But this time, I was the one lying in the PET scanner as it searched for possible evidence of spread of my aggressive prostate cancer . I spent those 30 minutes in quiet prayer. If that cancer had already spread to my lymph nodes, bones, lungs or brain, it could still be treated — but it would no longer be curable.

Why am I going public about this cancer that many men are uncomfortable talking about? Because I want to lift the veil and share lifesaving information, and I want all men to benefit from the medical research to which I’ve devoted my career and that is now guiding my care.

Five years before that fateful PET scan, my doctor had noted a slow rise in my PSA, the blood test for prostate-specific antigen. To contribute to knowledge and receive expert care, I enrolled in a clinical trial at the National Institutes of Health, the agency I led from 2009 through late 2021.

At first, there wasn’t much to worry about — targeted biopsies identified a slow-growing grade of prostate cancer that doesn’t require treatment and can be tracked via regular checkups, referred to as “active surveillance.” This initial diagnosis was not particularly surprising. Prostate cancer is the most commonly diagnosed cancer in men in the United States, and about 40 percent of men over age 65 — I’m 73 — have low-grade prostate cancer . Many of them never know it, and very few of them develop advanced disease.

Why am I going public about this cancer that many men are uncomfortable talking about? Because I want to lift the veil and share lifesaving information.

But in my case, things took a turn about a month ago when my PSA rose sharply to 22 — normal at my age is less than 5. An MRI scan showed that the tumor had significantly enlarged and might have even breached the capsule that surrounds the prostate, posing a significant risk that the cancer cells might have spread to other parts of the body.

New biopsies taken from the mass showed transformation into a much more aggressive cancer. When I heard the diagnosis was now a 9 on a cancer-grading scale that goes only to 10, I knew that everything had changed.

Thus, that PET scan, which was ordered to determine if the cancer had spread beyond the prostate, carried high significance. Would a cure still be possible, or would it be time to get my affairs in order? A few hours later, when my doctors showed me the scan results, I felt a rush of profound relief and gratitude. There was no detectable evidence of cancer outside of the primary tumor.

Later this month, I will undergo a radical prostatectomy — a procedure that will remove my entire prostate gland. This will be part of the same NIH research protocol — I want as much information as possible to be learned from my case, to help others in the future.

While there are no guarantees, my doctors believe I have a high likelihood of being cured by the surgery.

My situation is far better than my father’s when he was diagnosed with prostate cancer four decades ago. He was about the same age that I am now, but it wasn’t possible back then to assess how advanced the cancer might be. He was treated with a hormonal therapy that might not have been necessary and had a significant negative impact on his quality of life.

Because of research supported by NIH, along with highly effective collaborations with the private sector, prostate cancer can now be treated with individualized precision and improved outcomes.

As in my case, high-resolution MRI scans can now be used to delineate the precise location of a tumor. When combined with real-time ultrasound, this allows pinpoint targeting of the prostate biopsies. My surgeon will be assisted by a sophisticated robot named for Leonardo da Vinci that employs a less invasive surgical approach than previous techniques, requiring just a few small incisions.

Advances in clinical treatments have been informed by large-scale, rigorously designed trials that have assessed the risks and benefits and were possible because of the willingness of cancer patients to enroll in such trials.

I feel compelled to tell this story openly. I hope it helps someone. I don’t want to waste time.

If my cancer recurs, the DNA analysis that has been carried out on my tumor will guide the precise choice of therapies. As a researcher who had the privilege of leading the Human Genome Project , it is truly gratifying to see how these advances in genomics have transformed the diagnosis and treatment of cancer.

I want all men to have the same opportunity that I did. Prostate cancer is still the No. 2 killer of men. I want the goals of the Cancer Moonshot to be met — to end cancer as we know it. Early detection really matters, and when combined with active surveillance can identify the risky cancers like mine, and leave the rest alone. The five-year relative survival rate for prostate cancer is 97 percent, according to the American Cancer Society , but it’s only 34 percent if the cancer has spread to distant areas of the body.

But lack of information and confusion about the best approach to prostate cancer screening have impeded progress. Currently, the U.S. Preventive Services Task Force recommends that all men age 55 to 69 discuss PSA screening with their primary-care physician, but it recommends against starting PSA screening after age 70.

Other groups, like the American Urological Association , suggest that screening should start earlier, especially for men with a family history — like me — and for African American men, who have a higher risk of prostate cancer. But these recommendations are not consistently being followed.

Our health-care system is afflicted with health inequities. For example, the image-guided biopsies are not available everywhere and to everyone. Finally, many men are fearful of the surgical approach to prostate cancer because of the risk of incontinence and impotence, but advances in surgical techniques have made those outcomes considerably less troublesome than in the past. Similarly, the alternative therapeutic approaches of radiation and hormonal therapy have seen significant advances.

A little over a year ago, while I was praying for a dying friend, I had the experience of receiving a clear and unmistakable message. This has almost never happened to me. It was just this: “Don’t waste your time, you may not have much left.” Gulp.

Having now received a diagnosis of aggressive prostate cancer and feeling grateful for all the ways I have benefited from research advances, I feel compelled to tell this story openly. I hope it helps someone. I don’t want to waste time.

Francis S. Collins served as director of the National Institutes of Health from 2009 to 2021 and as director of the National Human Genome Research Institute at NIH from 1993 to 2008. He is a physician-geneticist and leads a White House initiative to eliminate hepatitis C in the United States, while also continuing to pursue his research interests as a distinguished NIH investigator.

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