Strong sensitivity of the global mean OH concentration and the tropospheric oxidizing efficiency to the source of NOx from lightning

Production of nitrogen oxides (NO x = NO + NO 2 ) by lightning (LtNO x ) is the most uncertain among the global NO x sources, with recent estimates ranging from about 1–20 Tg(N)/yr. Previous studies of LtNO x have focused mainly on its role in the tropospheric NO y (reactive nitrogen) and O 3 budgets. We show that the global mean OH concentration is also very sensitive to LtNO x . Furthermore, despite the fact that the largest changes in NO x due to lightning are in the upper troposphere, where reactions with OH are generally slower, we find that the sensitivity of the mean tropospheric lifetime of methane (CH 4 ) and methylchloroform (CH 3 CCl 3 ) to assumptions about LtNO x are as large as the sensitivity of the tropospheric O 3 burden. Thus, an improved understanding of LtNO x will be important for our ability to accurately simulate the tropospheric oxidizing efficiency and its changes over time.