Significant contribution of lightning NOx to summertime surface O3 on the Tibetan Plateau

Abstract

Lightning generates nitrogen oxides (NOx) in the troposphere, an important precursor of tropospheric ozone (O3). The Tibetan Plateau (TP) is considered to be a global atmospheric background location with limited anthropogenic influences. However, the observed summertime surface O3 concentration on the TP is 25% higher than that in highly polluted regions (e.g., southern China). Previous studies have suggested that lightning-produced NOx (LNOx) can affect the concentration of surface O3. 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 LNOx to the surface O3 budget on the TP. Our results showed that LNOx contributed approximately 15% of the surface NOx emission on the TP in summer. Accordingly, the contribution of LNOx to the summertime surface daily maximum 8-h average (MDA8) O3 on the TP was 9.3 ± 7.1 ppb, which was 17.5% ± 14.5% of the total concentration of the surface MDA8 O3. In addition, our study found that the number of moles of NO produced per lightning flash (LNOx production efficiency) significantly affected the surface concentration of NOx, OH, and MDA8 O3. Increasing the LNOx production efficiency (PE) from 0 to 330 mol NO flash−1 increased the concentration of MDA8 O3 by up to 20% on the TP. Our study revealed that lightning significantly affects the atmospheric chemical processes involving O3 on the TP.