We describe a multi-scale framework for assessing the impact of the aviation sector on air quality and human health globally. Four conceptual scales are identified: plume (~1 km), local (~10 km), regional (~100-1000 km), and global (~10,000 km). We show how processes at all scales determine the impact of aviation on air quality in urban environments.

First, we describe the aircraft plume scale. We draw upon recent experimental work with LIDAR and high frequency ambient air quality modeling stations, and our recent plume modeling work, to illustrate the impact of near-field plume dynamics on pollutant concentrations in the immediate airport vicinity.

Second, we consider the local scale. As many airports are situated in urban areas it necessary to determine local peaks in pollutant concentrations attributable to aviation, as this determines the health risk of populations near airports. We apply recent algorithm developments in dispersion modeling to rapidly estimate air quality impacts at several airports.

Third, the regional scale. We describe how secondary particulate matter dominates health impacts overall, and illustrate hybrid local dispersion/regional chemistry-transport modeling for airports.

Fourth, the global scale is analyzed. We present recent modeling work indicating that intercontinental pollution from aircraft cruise emissions impacts air quality.

Finally we compare the contributions of each scale to air quality degradation and health risk in cities. While near-airport peak pollution concentrations due to aircraft landing and takeoff operations result in relatively small populations being exposed to relatively high health risks, the intercontinental component of pollution from aircraft cruise emissions gives rise to relatively large populations being exposed to relatively low increases in health risk attributable to aviation. Estimates for total premature mortalities attributable to airport and cruise emissions are given.