Significant contribution of lightning NO <subscript>x</subscript> to summertime surface O <subscript>3</subscript> on the Tibetan Plateau.

Lightning generates nitrogen oxides (NO x ) in the troposphere, an important precursor of tropospheric ozone (O 3 ). The Tibetan Plateau (TP) is considered to be a global atmospheric background location with limited anthropogenic influences. However, the observed summertime surface O 3 concentration on the TP is 25% higher than that in highly polluted regions (e.g., southern China). Previous studies have suggested that lightning-produced NO x (LNO x ) can affect the concentration of surface O 3 . We used the Weather Research and Forecasting coupled with chemistry (WRF-Chem) model combined with satellite, ground-based, and airborne observations to evaluate the contribution of LNO x to the surface O 3 budget on the TP. Our results showed that LNO x contributed approximately 15% of the surface NO x emission on the TP in summer. Accordingly, the contribution of LNO x to the summertime surface daily maximum 8-h average (MDA8) O 3 on the TP was 9.3 ± 7.1 ppb, which was 17.5% ± 14.5% of the total concentration of the surface MDA8 O 3 . In addition, our study found that the number of moles of NO produced per lightning flash (LNO x production efficiency) significantly affected the surface concentration of NO x , OH, and MDA8 O 3 . Increasing the LNO x production efficiency (PE) from 0 to 330 mol NO flash -1 increased the concentration of MDA8 O 3 by up to 20% on the TP. Our study revealed that lightning significantly affects the atmospheric chemical processes involving O 3 on the TP.

Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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