An Inter-comparative Study of the Effects of Aircraft on Surface Air Quality

This study inter-compares, among five global models, the potential impacts of all commercial aircraft emissions worldwide on surface ozone and PM2.5. The models include climate-response models (CRMs) with interactive meteorology, chemical-transport models (CTMs) with prescribed meteorology, and models that integrate aspects of both. Previously, few studies have addressed the effects of cruise-altitude aircraft emissions on surface air quality, and each has provided a marginally different result. Here, model inputs are substantially harmonized in an effort to achieve a consensus about the state of understanding of impacts of 2006 commercial aviation emissions. Whereas, all models find that aircraft increase near-surface ozone (0.4 to 1.9% globally), perturbations in the Northern Hemisphere are highest in winter, when ambient ozone levels are lower and potentially of not as much concern to human health compared to the higher ozone in the summer months. Changes in surface-level PM2.5 in the CTMs (0.14 to 0.4%) and CRMs (-1.9 to 1.2%) may depend on highly-varying background aerosol fields among models and the inclusion of feedbacks between aircraft emissions and changes in meteorology. The CTMs tend to show an increase in surface PM2.5 primarily over high-traffic regions in the North American mid-latitudes. The CRMs, on the other hand, demonstrate the effects of changing meteorological fields and potential feedbacks on aviation emission impacts, and exhibit large perturbations over regions where natural emissions (e.g., soil dust and sea spray) are abundant. Excluding these emissions in the CRMs results in a smaller-in-magnitude surface change due to aviation. The changes in ozone and PM2.5 found here may be used to estimate ranges in the net impacts of aircraft on human health.