Ranking of top five flights by O<sub>3</sub> impact for two different metrics

<p><b>Table 2.</b>  Ranking of top five flights by O<sub>3</sub> impact for two different metrics. The first section shows ranking by total impact, i.e. the contribution of each flight to the total ozone perturbation. The second section shows ranking by FOF, i.e. ozone impact normalized by fuel burn and scaled by the lowest impact flight. Return trips were not counted (only the higher of a return-trip pair are counted). </p> <p><strong>Abstract</strong></p> <p>Aviation NO<sub><em>x</em></sub> 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<sub><em>x</em></sub> on O<sub>3</sub> in large geographic regions. As these studies have applied forward modeling techniques, it has not been possible to attribute O<sub>3</sub> 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 O<sub>3</sub> production due to aviation NO<sub><em>x</em></sub> emissions, which is the first application of an adjoint to this problem. We find that total aviation NO<sub><em>x</em></sub> emitted in October causes 40% more O<sub>3</sub> than in April and that Pacific aviation emissions could cause 4–5 times more tropospheric O<sub>3</sub> per unit NO<sub><em>x</em></sub> than European or North American emissions. Using this sensitivity approach, the O<sub>3</sub> burden attributable to 83 000 unique scheduled civil flights is computed individually. We find that the ten highest total O<sub>3</sub>-producing flights have origins or destinations in New Zealand or Australia. The top ranked O<sub>3</sub>-producing flights normalized by fuel burn cause 157 times more normalized O<sub>3</sub> formation than the bottom ranked ones. These results show significant spatial and temporal heterogeneity in environmental impacts of aviation NO<sub><em>x</em></sub> emissions.</p>