Total ozone impact normalized by seat-km

<b>Table 3.</b> Total ozone impact normalized by seat-km. <strong>Abstract</strong> Aviation NO_<em>x</em> emissions promote tropospheric ozone formation, which is linked to climate warming and adverse health effects. Modeling studies have quantified the relative impact of aviation NO_<em>x</em> 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 NO_<em>x</em> emissions, which is the first application of an adjoint to this problem. We find that total aviation NO_<em>x</em> 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 NO_<em>x</em> 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 NO_<em>x</em> emissions.