Temporal and spatial variability in the aviation NOx-related O3 impact

Aviation NOx emissions promote tropospheric ozone formation, which is linked to climate warming and adverse health effects. Modeling studies have quantified the relative impact of aviation NOx on O3 in large geographic regions. As these studies have applied forward modeling techniques, it has not been possible to attribute O3 formation to individual flights. Here we apply the adjoint of the global chemistry–transport model GEOS-Chem to assess the temporal and spatial variability in O3 production due to aviation NOx emissions, which is the first application of an adjoint to this problem. We find that total aviation NOx emitted in October causes 40% more O3 than in April and that Pacific aviation emissions could cause 4–5 times more tropospheric O3 per unit NOx than European or North American emissions. Using this sensitivity approach, the O3 burden attributable to 83 000 unique scheduled civil flights is computed individually. We find that the ten highest total O3-producing flights have origins or destinations in New Zealand or Australia. The top ranked O3-producing flights normalized by fuel burn cause 157 times more normalized O3 formation than the bottom ranked ones. These results show significant spatial and temporal heterogeneity in environmental impacts of aviation NOx emissions.