| Summary: | Aviation NO _x 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 _x on O _3 in large geographic regions. As these studies have applied forward modeling techniques, it has not been possible to attribute O _3 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 _3 production due to aviation NO _x emissions, which is the first application of an adjoint to this problem. We find that total aviation NO _x emitted in October causes 40% more O _3 than in April and that Pacific aviation emissions could cause 4–5 times more tropospheric O _3 per unit NO _x than European or North American emissions. Using this sensitivity approach, the O _3 burden attributable to 83 000 unique scheduled civil flights is computed individually. We find that the ten highest total O _3 -producing flights have origins or destinations in New Zealand or Australia. The top ranked O _3 -producing flights normalized by fuel burn cause 157 times more normalized O _3 formation than the bottom ranked ones. These results show significant spatial and temporal heterogeneity in environmental impacts of aviation NO _x emissions.
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