Summary of Findings

The purpose of this study was to evaluate and update the existing body of knowledge on air quality and public health studies related to airports to help airport operators better understand and respond to airport-related air quality and public health concerns. This section provides a summary of the basic findings presented for a broad readership. More detailed technical information on specific topics and studies is provided in the body of the report.

This report builds upon and updates Airport Cooperative Research Program (ACRP) Report 135: Understanding Airport Air Quality and Public Health Studies Related to Airports, prepared for ACRP in 2015. The goal of the current research is to provide needed updates to Report 135, including the expansion or addition of some topics. The primary topics for expansion in this effort include ultrafine particles (UFPs, or particulate matter (PM) with an aerodynamic diameter less than 0.1 µm), indoor air pollution, and environmental justice (EJ) concerns related to airports. The current work was accomplished through a review of literature and a synthesis of the conclusions of the studies, primarily focusing on studies published since the publication of ACRP Report 135. This involved summarizing, corroborating, and critically reviewing findings from the identified literature to extract general conclusions applicable to most airports. Because it is difficult to generalize to all airports, some conclusions were qualified to indicate that findings at specific airports may differ.

To assist airport managers and operators, this report provides primer-type information on fundamental air quality concepts, airport sources and emissions, and air quality impacts and health risks relevant to airports in Chapters 2 through 4. These sections provide background information to support an understanding of the conclusions drawn from the synthesis. In addition, Appendix C, Frequently Asked Questions (FAQs), provides answers to popular questions. Chapter 5 presents the synthesis work shaped in the form of two basic questions: (1) What pollutants emitted at airports are of greatest concern? (2) What are the airport’s contributions to local air quality and health impacts? The key findings for airports are as follows:

• Factors that affect airport contributions to local air quality and public health—There are many factors that can affect airport contributions to local air quality and public health. These include pollutant type, toxicity, the magnitude of emissions (largely affected by source characteristics and operations), and human exposure. In addition, an individual’s characteristics, such as age, gender, race/ethnicity, socioeconomic status, pre-existing disease status, and co-exposures to other risk factors, can affect a person’s or a population’s susceptibility and vulnerability to air pollutants. See Section 4.2 and the FAQs.
• Ability to state conclusions for specific airports—Because all airports are different, it is very difficult to make general statements about airport air quality contributions and health impacts. Airport contributions to air quality depend on many different factors including, but not limited to, airport source types (e.g., aircraft fleet mixes), source operations, airport layout and location, surrounding geography and land uses, and meteorology. The airport pollutant exposures and related health impacts will be related to the proximity of residential areas (and other sensitive receptors) to an airport. See Sections 3.1–3.5.
• Ability of airports to reduce air quality impacts and public health impacts—Airports are complex facilities with a broad mix of source types contributing to air quality and health concerns. However, airport operators have little or no control over a majority of the airport emission sources. For example, airport operators do not have the authority to set emission

standards for aircraft, airport equipment, and airport vehicles which constitute the vast majority of an airport’s emissions. At best, airport operators can influence the owners of these sources to reduce emissions through best operational practices, for example by incentivizing the use of aircraft, engines, and vehicles meeting the most stringent emission standards, operating on fuels with the lowest emissions, and other operational practices.

• Pollutant(s) that pose the biggest health risk at airports—Airport risk assessment studies have shown that fine PM (PM_2.5) dominates as a contributor to the overall health risks posed by airport emissions. The risks associated with exposure to fine particles are orders of magnitude higher than those associated with the next highest contributor, the hazardous air pollutant (HAP) formaldehyde. PM_2.5 levels have been found to vary significantly at different airports. See Chapter 4 and Section 5.1.
  • Secondary PM (PM not directly emitted from a source but formed in the atmosphere) at airports—Studies indicate that secondary PM may form at significant distances downstream from an airport (many miles) adding to health impacts, and thus, requiring large-scale (e.g., regional) modeling to determine overall PM health impacts. See Section 5.2.
  • Airport contributions of UFPs (PM sized below 0.1 µm diameter)— UFPs from aircraft are the subject of increasing public health-related concerns because they can travel even further in the human respiratory tract than fine PM, with a potential to cause more pulmonary inflammation than fine PM. Measurement studies have shown that UFP concentrations tend to be highly elevated near airport runways and, unlike UFP impacts from ground vehicles, which tend to fall off rapidly with distance from roadways, elevated aircraft-related UFP concentrations have been measured at distances of up to 600 m downwind of an airport. The characteristics (size and particle number counts) of UFPs emitted by aircraft can be distinguished from those emitted by roadway vehicles. See Chapter 4 and Section 5.2.
  • Consistency of airport contributions of HAPs—Emissions of HAPs from airports and other area sources, and the resultant concentrations of HAPs measured at airports, vary from study to study. While some studies suggest that HAP concentrations near airports are similar to background levels, other studies suggest that airport emissions may cause elevated concentrations of some HAPs. The discrepancy in results may be due, in part, to uncertainties regarding the emission sources contributing to the measured concentration levels as well as differences in the time frames of measurements (e.g., continuous measurements versus measurements collected from 24-hour canister samples). See Section 5.2.
  • Lead as a concern at airports—Lead is a health concern at and near GA airports due to the use of leaded AvGas. Note that jet fuel (which is the most common fuel used in commercial aviation) does not contain lead. Current studies indicate that elevated ambient levels of lead associated with airport emissions can be measured at distances close to 1,000 meters downwind of an airport. Due to the public health concerns associated with lead in AvGas, in October 2023, the Environmental Protection Agency (EPA) issued a final determination that emissions of lead from aircraft that operate on leaded fuel cause or contribute to air pollution which may reasonably be anticipated to endanger public health and welfare under the Clean Air Act. See Section 5.2.

• Airport air quality and public health research—In most cases, the state of airport air quality and health research is currently inadequate to allow definitive conclusions. As such, all conclusions should be considered snapshots in time and uncertainties and limitations of the study should be defined, because future research may provide greater insights. Additionally, each airport has unique considerations when considering air quality and health impacts, so conclusions applicable to one airport should not be generalized to apply to all airports. See Chapter 5 and Appendices A and B.
• Indoor air quality at airports—The quality of indoor air at airports received heightened scrutiny during the COVID-19 pandemic. Studies have shown elevated pollutant levels, particularly of fine PM, at some locations within airports, with gate departure areas of the terminals frequently showing the highest indoor pollutant levels. Improved heating, ventilation, and air conditioning (HVAC) and filtration systems have been shown to successfully reduce indoor pollutant concentrations. See Section 5.2.1.
• Environmental Justice (EJ) concerns at airports—Airport emissions place a health burden on nearby residences. In many cities, the neighborhoods near airports contain a majority percentage of people of color and other communities with EJ concerns. Research has shown that these communities are often exposed to elevated pollutant concentrations in part due to airport activities, which contribute to health burdens on these residents. See section 5.2.5.