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41 C H A P T E R 6 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 necessary. Although the current state of research allows one to âpaint a pictureâ 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 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. The more pertinent issue is in quantifying the contributions. 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 PM (PM2.5) dominates 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. 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. 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 sur- rounding communities, although with appreciable contributions closer to the emission sources and variable conclusions depending on background levels. Although health effects of criteria gases are well defined, quantitative health risk assessments for these gases are relatively limited in comparison to ozone and PM. Because of the nature of ozone chemistry, ozone levels around airports tend to be lower than background levels (i.e., airports tend to be a sink for ozone). Although ozone levels in the vicin- ity 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. Lead is a concern at GA airports and will continue to be an issue as AvGas continues to be used. Current studies indicate that lead emissions can noticeably persist at distances close to Conclusions
42 Understanding Airport Air Quality and Public Health Studies Related to Airports 1,000 meters downwind of an airport. As such, studies indicate that lead contributions near GA airports may not be negligible. 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 black carbon, nitrates, and sulfates need to be taken into account as well as PM size distributions. In addition to the suspected health concerns of ultrafine PM (along the lines of the current understanding of PM2.5), measurement studies have shown that ultrafine concentrations tend to be highly elevated near an airport (near runways) with persistence above background levels at distances of 600 meters downwind of an airport. As such, ultrafine PM generated by airports is suspected of having a broader impact than that generated by roadway vehicles. Concentrations of HAPs at airports seem to vary. Although some studies suggest that HAP concentrations near airports may be similar to background levels, there appears to be enough evidence suggesting otherwise, however, there are noticeable uncertainties concerning the actual concentration levels. 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.