CHAPTER 6: Conclusions
Since 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 can depend on many different factors including, but not limited to, airport source types (e.g., aircraft fleet mixes), airport layout and location, geography, and meteorology. Contributions to population health impacts depend on these factors as well as population patterns and vulnerability attributes.
Although there have been increasing amounts of research on airport contributions to local air quality health impacts, more research is still necessary. Although the current state of research allows one to “paint a picture” of current understanding in this area, it should be considered as a snapshot in time since future research may provide further details. The current research efforts appear to be aligned with the prioritization of pollutant health risks. Based on the relative number of studies and the recent focus, available resources appear to be correctly being applied to PM (including UFPs) and HAPs research, with consideration of ozone for regional-scale analyses.
Regarding airport contributions to local air quality, studies have shown that airport emissions and resulting concentration contributions can be well correlated to airport operations (e.g., aircraft usage) as part of source identification and apportionment work. Airport and major roadway monitoring indicated airport emissions can be identified by their high UFP particle counts and narrow particle size distribution. Traffic emissions have wide particle size distributions and less dominance of UFPs. They are also higher in coarse PM and BC. The current research efforts appear to be aligned with the need for further measurements and an understanding of health impacts.
Risk assessments have shown that fine PM2.5 and UFPs dominate the overall health risks posed by airport emissions. The risk for fine particles is orders of magnitude higher than that for the closest HAP, formaldehyde, although the ability to quantify the non-cancer health effects of HAPs is limited. PM2.5 levels have been found to vary significantly at different airports. UFPs emitted by aircraft have higher pulmonary deposition rates as they bypass the human body’s filtration defense. The smaller the particle diameter, the higher the toxicity Although PM10 is a health concern, the fact that much of the coarser portion is filtered out by the upper respiratory tract in human beings makes it of less concern than the finer particles.
Some studies appear to indicate that most criteria gases (e.g., CO, NO2, and SO2) generated from airports generally tend to result in similar concentrations to background (or urban) levels in surrounding communities, although with appreciable contributions closer to the emission sources and variable conclusions depending on background levels. Some studies argue CO concentrations are from motor vehicles near airports (SCAQMD 2010). Contrarily, other studies linked elevated criteria gases to airport emissions. One study that examined COVID-19 travel lockdowns in Singapore on ambient pollution found a significant decrease in NO2 and SO2 concentrations and minor reductions in CO (Li & Tartarini, 2020). Another study found airports contribute 15–22% and 40–50% of CO to pollutant monitors in winter and summer, respectively (Tetra Tech 2013). These inconsistencies in results indicate greater modeling and measurement studies must be conducted to understand the origins and transport of criteria gases.
Although ozone levels in the vicinity of an airport may be depressed, airports can contribute to the formation of ozone on a larger regional level, thus resulting in increased health impacts. Children are especially impacted by ozone exposure, causing increased asthma hospitalizations and neurological effects.
Lead is a concern at GA airports and will continue to be an issue as long as leaded AvGas continues to be used. Current studies indicate that lead emissions can noticeably persist at distances
close to 1 kilometer downwind of an airport. Children who live within 1 km of an airport had higher lead blood levels than other children. As such, studies indicate that lead contributions near airports may not be negligible. A national analysis of model-extrapolated estimates of airborne lead at 13,000 U.S. airports found ambient that “the model-extrapolated lead estimates in this study indicate that some additional U.S. airports may have air lead concentrations above the NAAQS,” but that “lead concentrations decrease to below the standard within 50 meters from the area of highest concentration.” (EPA, 2023) In response to studies showing the potential health impacts related to leaded AvGas, EPA issued a final endangerment finding in October 2023 indicating that lead emissions from aircraft engines using leaded fuel cause or contribute to air pollution that may reasonably be anticipated to endanger public health. EPA and FAA now have the responsibility to propose regulatory standards for lead emissions from certain aircraft engines (EPA) and standards to control or eliminate lead emissions from aircraft fuel or fuel additives (FAA).
Studies indicate that secondary PM may form at significant distances downstream from an airport (many miles), adding to health impacts thus, requiring large-scale (e.g., regional) modeling to determine overall PM health impacts. In addition, the impacts of different PM components including BC, nitrates, and sulfates need to be taken into account as well as PM size distributions.
Measurement studies have shown that UFP concentrations tend to be highly elevated near an airport (near runways) with persistence above background levels more than 8 kilometers downwind of an airport (Austin et al., 2021; Hudda & Fruin, 2016; Keuken et al., 2015). As such, UFPs generated by airports are suspected of having a broader impact than that generated by roadway vehicles. UFP inhalation is significantly correlated to systolic blood pressure, hypertension, and eosinophilic airway inflammation in adults and children. Health impacts were greater with children because of higher pulmonary lung deposition.
Concentrations of HAPs at airports seem to vary. Although some studies suggest that HAP concentrations near airports may be like background levels, there appears to be enough evidence suggesting otherwise, however; there are noticeable uncertainties concerning the actual concentration levels. PAH aircraft emissions were also found to be elevated at airports. PAHs measured were predominantly Naphthalene and Phenanthrene.
Aviation emissions are highly impacted by jet fuel composition. AJFs are from non-petroleum sources and burn cleaner than standard jet fuel. AJFs would supplement AvGas as a blend ranging from 10-50% AJF fuel.
Indoor airport studies found PM and other pollutants infiltrate into the airport. Concentrations are relatively low compared to ambient levels (indoor/outdoor PM2.5 ratio= 0.33) (Kim et al., 2020). Indoor air pollution events corresponded to aircraft traffic and passenger movement. Passengers are most exposed to PM, BC, and other pollutants in areas open to ambient air, i.e., arrivals, departures, and aircraft loading and disembarking. Indoor airport workers displayed relatively low health impacts. The greatest exposures were measured in outdoor airport workers, predominantly jet fuel workers and baggage handlers. Jet fuel workers’ breath samples indicated exposures of more than 100 times greater compared to a control group.
Airport emissions may contribute to the health burden on residents of nearby communities. Historically marginalized communities are more likely to live near airports due to (1) locally undesirable land uses and (2) less power to resist. Studies found elevated UFPs and CO were correlated to greater minority populations, less income, and less education. In many cities studied, a majority percentage of minority populations live near the airport. Airport communities have higher rates of cancer, heart disease, shorter life expectancy, etc. Children living within 10 miles
of an airport are less likely to graduate from high school, more likely to be born premature, and have higher lead levels in their blood.
Health assessments involving a system-level scope (i.e., involving many airports) appear to provide useful statistics on both total and average airport risks with the understanding that individual airport studies also need to be conducted, the results of which may differ significantly.
