Sensitivity of the ozone layer, climate, and public health to changes in the location of aviation emissions

Abstract

Aviation’s impact on the ozone layer, climate, and air quality varies based on the location of emissions. Changes from subsonic aircraft emissions due to regional growth, and the potential re-introduction of supersonic transport flying in the stratosphere present new scenarios that regulations do not currently address. To quantify the atmospheric impacts of aviation emissions, past studies have used global chemistry-transport models. However, these models are not practical in the context of policy analysis because of their high computational costs and lack of uncertainty quantification to support decision-making. Using atmospheric emission sensitivities derived from the GEOS-Chem chemistry-transport model, I develop a new reduced- order, probabilistic model to calculate the ozone, climate, and air quality impacts from aircraft emissions for a full range of possible flight altitudes and latitudes. The current model reports results based on the average of five years of atmospheric impacts. Applying this model to multiple emission scenarios, this thesis explores the variation in environmental impacts across subsonic flights on the basis of flight distance, and across potential supersonic flights with differing cruise altitudes.

Results show that short-haul flights have the greatest air quality-related health impacts per unit of NOx emissions compared to mid- and long-haul flights. These differences are driven by surface PM2.5 changes, which lead to ~8400 premature mortalities per Tg NOx from short-haul emissions, about 1.6-1.8 times greater than estimates from mid- and long-haul NOx emissions. The results from subsonic and supersonic fleet indicate that the ozone, climate, and air quality impacts from NOx are most sensitive to changes in the altitude of emissions. Subsonic emissions are estimated to increase the global ozone column by 0.33 Dobson Units (DU) per Tg NOx, while a supersonic fleet flying 18-21 km causes 6.6 DU of ozone destruction per Tg NOx. However, this stratospheric ozone depletion also leads to ~13,000 fewer mortalities per Tg NOx from decreased population exposure to surface ozone. As changing aircraft emissions introduce a variety of new environmental consequences and tradeoffs, understanding the sensitivity of atmospheric impacts to the emission location is essential to inform policies and future aircraft technologies.