CHAPTER 7: Recommendations for Future Research

The following provides a summary of the existing knowledge gaps and recommended future research to help advance the understanding of airport air quality contributions and public health impacts.

• In general, more health-related research is necessary to gain a better understanding of airport air quality contributions and health impacts. This includes more airport air quality monitoring programs and additional health risk assessments that should involve both airport and system levels. Understanding the health risks attributable to an individual airport requires atmospheric modeling and health risk assessment specific to the individual airport, and these efforts would provide insight to individual airport operators.
• Since, from recent risk assessments, PM seems to pose the greatest risk to human health, more specific characterization studies of fine particles (PM_2.5), UFPs, PM components, and size distributions are necessary. Health effects and risks of UFPs and PM components (e.g., nitrates, sulfates, etc.) are not well understood. While many studies have been undertaken in recent years on UFPs, additional research is needed in this area due to the significant potential health impacts.
• Further research is also needed on who is at greatest risk from UFPs attributed to airport operations (e.g., outdoor airport workers, passengers and employees inside the airport, communities downwind of aircraft), what the greatest health concerns are for each of these groups, and what measures can be taken to reduce the health risks from these UFP exposures. Additionally, more research is needed on emission rates of UFPs from aircraft and other engines as well as more research on what further differences may exist between primary PM directly emitted from aircraft versus secondary PM formed in the atmosphere, as well as emitted from other sources (e.g., roadway vehicles).
• More research on the overall risks posed by lead emissions from GA aircraft is necessary and underway. Aircraft lead emissions have been found to constitute health risks, especially for children. FAA and affected stakeholders are researching pathways towards eliminating leaded fuels in piston-engine aircraft by 2030. EPA and FAA are considering actions to regulate these emissions.
• Modeling uncertainties need to be better understood so that health risk assessments can be made more reliable with clearer (or smaller) error bands. This includes uncertainties in emissions inventories, atmospheric dispersion models, and in the underlying health evidence.
• With the importance of PM_2.5 and UFP health impacts, the PM emissions data, as well as emissions of particle precursors (VOCs, NO_x, SO₂), need to be as accurate as possible. More mass and size-based PM measurements of aircraft engines would enable development of a more accurate set of emission factors (emissions indices).
• Multi-pollutant epidemiological investigations would be beneficial for assessing potential synergies and interactions of different pollutants on health effects.
• In addition to risks placed on the public, more assessments conducted on airport workers (e.g., GSE operators) would lead to a better understanding of impacts on those who are much closer to the sources and have longer exposure times. Also, more studies (with measurements) on the risks to airport passengers would further our understanding.
• Further research is needed to determine aircraft power setting (and operations) influences on emitted PM characteristics, including size and chemical characteristics.

• Research to improve aircraft taxiing/idle and engine start emissions modeling would be beneficial, as these transient conditions tend to have different emissions characteristics than steady-state conditions.
• Local atmospheric chemistry modeling would benefit from further investigation. Although CMAQ has a large set of chemistry mechanisms, it uses larger grid sizes that make finer spatial resolution assessments difficult. Nested modeling capabilities can be applied, but require greater resources, and there remains the need to use ambient monitoring to validate dispersion modeling outputs.
• Rather than using the typical 1-hour or coarser concentrations from models like AERMOD, time-varying models may be investigated to provide more robust modeling environments to conduct health risk assessments.
• More research is needed on the health impacts of airports on EJ communities. This includes a broad look at health care in general in EJ communities, understanding the key pollutants and exposures within these communities, and working with these communities to address existing airport-related health problems and developing strategies to eliminate or mitigate these impacts where possible.
• While indoor air pollution at airports does not appear to be a major concern, additional studies are warranted, particularly focusing on airport workers with the greatest potential exposures to indoor air pollution. Continued advances in building ventilation and filtration systems could be pursued and implemented.