Adjoint sensitivity analysis of the intercontinental impacts of aviation emissions on air quality and health

Abstract

Over 10,000 premature mortalities per year globally are attributed to the exposure to particulate matter caused by aircraft emissions. Unlike previous studies that focus on the regional impacts from the aircraft emissions below 3,000 feet, this thesis studies the impact from emissions at all altitudes and across continents on increasing particulates in a receptor region, thereby increasing exposure. In addition to these intercontinental impacts, the thesis analyzes the temporal variations of sensitivities of the air quality and health, the proportion of the impacts attributable to different emission species, and the background emissions' influence on the impact of aircraft emissions. To quantify the impacts of aircraft emissions at various locations and times, this study uses the adjoint model of GEOS-Chem, a chemical transport model. The adjoint method efficiently computes sensitivities of a few objective functions, such as aggregated PM concentration and human exposure to PM concentration, with respect to many input parameters, i.e. emissions at different locations and times. Whereas emissions below 3,000 feet have mostly local impacts, cruise emissions from North America impair the air quality in Europe and Asia, and European cruise emissions affect Asia. Due to emissions entering Asia, the premature mortalities in Asia were approximately two to three times larger than the global mortalities caused by the Asian emissions. In contrast, North America observed only about one-ninth of the global premature mortalities caused by North American emissions because emissions get carried out of the region. This thesis calculates that most of the premature mortalities occured in Europe and Asia in 2006. Sensitivities to emissions also have seasonal and diurnal cycles. For example, ground level NOx emissions in the evening contribute to 50% more surface PM formation than the same emissions in the morning, and cruise level NOx emissions in early winter cause six times more PM concentration increase than the same emissions in spring. Aircraft NOx emissions cause 78% of PM from aviation emissions, and given the population exposure to PM concentration increase, NOx contributes 90% of the total impact. By showing the second-order sensitivities, this study finds that increases in background emissions of ammonia increase the impact of aircraft emissions on the air quality and increases in background NOx emissions decrease the impact. These results show the effectiveness of the adjoint model for analyzing the longterm sensitivities. Some of the analyses presented are practically only possible with the adjoint method. By regulating emissions at high sensitivities in time and region, calculated by the adjoint model, governments can design effective pollutant reduction policies.