Effects of Nitrogen Oxides Produced from Lightning on the Formation of the Ozone Valley over the Tibetan Plateau

In order to further study possible influences of the photocatalytic reaction on the formation of O₃ and O₃ valley in the summer over the Tibetan Plateau, NO₂ VCD, O₃ total column and O₃ profiles from OMI and OTD (Optics Transient Detection)/LIS (Lightning Imaging Sensor) total lightning data are used to investigate the spatial and temporal distributions characteristics of TOC and NO₂ VCD, the correlation between lightning and NO₂ VCD, the vertical distribution of O₃ and its relationship with LNO_x in the Tibetan Plateau and the Yangtze River Delta. Results in the two regions, which are located at the similar latitudes, are compared and analyzed. It is found that the O₃ valley over the Tibetan Plateau mainly appears in the summer and autumn, and its TOC value is about 10-15 DU (Dobson unit) lower than that over the Yangtze River Delta. The NO₂ VCD over the Tibetan Plateau is relatively small, and exhibits a temporal distribution characteristic of low in the summer and high in the winter. The total concentration of O₃ in the Tibetan Plateau generally decreases in the summer due to the effect of the South Asia high. However, due to the influence of strong thunderstorms, the concentration of LNO_x in the upper troposphere increases and can be transported to the top of the troposphere by strong ascending flows, which subsequently increases the concentration of O₃ by photochemical reaction. Thereby, the O₃ concentration difference between the Tibetan Plateau and the same latitude region is reduced and the decrease of the total O₃ concentration slows down, which inhibits further deepening of the O₃ valley in the Tibetan Plateau in the summer.