Sensitivity of total tropospheric O<sub>3</sub> to aviation NO<sub><em>x</em></sub> emissions (black); ozone production efficiency (blue) weighted by aviation NO<sub><em>x</em></sub> emissions; aviation-attributable ozone production rate (green); aviation-attributable ozone lifetime (red); all with one month averages (thick line) and normalized by annual mean, which is 3.2 kg O<sub>3</sub> / kg NO<sub><em>x</em></sub> (black), 17.5 (blue), 1375 molecules cm<sup>−3</sup> s<sup>−1</sup> (green), 26.9 days (red)

<p><strong>Figure 1.</strong> Sensitivity of total tropospheric O<sub>3</sub> to aviation NO<sub><em>x</em></sub> emissions (black); ozone production efficiency (blue) weighted by aviation NO<sub><em>x</em></sub> emissions; aviation-attributable ozone production rate (green); aviation-attributable ozone lifetime (red); all with one month averages (thick line) and normalized by annual mean, which is 3.2 kg O<sub>3</sub> / kg NO<sub><em>x</em></sub> (black), 17.5 (blue), 1375 molecules cm<sup>−3</sup> s<sup>−1</sup> (green), 26.9 days (red).</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>