Study On The Impact Of LNO_x On The Low Ozone Area In The Qinghai-Tibet Plateau Based On Satellite Data And WRF-Chem Mode

To verify the effect of lightning-induced nitrogen oxides（LNO_x）on nitrogen oxides（NO_x=NO+NO₂）,tropospheric column ozone（O₃）,and O₃ at various altitude ranges on the Tibetan Plateau（TP）and its surrounding areas,we initially utilized LIS/OTD and OMI grid data to examine the correlation between lightning and tropospheric NO₂ vertical column density（NO₂VCD）on the TP during 2005-2013.Subsequently,employing the WRF-Chem model,the source of LNO_x and its contribution to the vertical column concentration of NO_x on the TP in July 2010 were examined.The local LNO_x on the TP and transported LNO_x were distinguished.Finally,using the WRF-Chem model,total LNO_x and its impact on the TP ozone valley were investigated.Additionally,the impact range of LNO_x from different sources on the O₃ of the TP was assessed,and the main conclusions are summarized as follows:（1）Although monthly variability trends indicate a positive correlation between lightning and NO₂VCD on the TP,NO₂VCD actually decreases with an increase in lightning.This positive correlation all but disappears on an interannual level.The simulation of LNO_x and NO_xon the TP using WRF-Chem shows that while LNO_x is a significant source of NO_x,non-lightning sources also have a notable impact on vertical NO_x concentration.Thunderstorms generate LNO_x which is then transported to the TP.Due to the non-linear effects of diffusion and chemistry,changes in LNO_x don’t necessarily result in a corresponding change in NO_x.These three factors provide an explanation for the satellite observations.（2）As a whole,LNO_x contributes to the increase of O₃ levels on the TP.However,the magnitude of the increment is relatively small in comparison to the low base level of O₃.This suggests that the impact of LNO_x on O₃ changes on the TP is minor.When there is a slight decrease in LNO_x on the plateau,the increment of O₃ levels in the southern part of the area decreases,while that in the central and northern parts increases instead.These results indicate that the control areas for O₃ in the southern and northern parts of the TP are different.Thus,when there are changes in LNO_x in the region,a local-specific analysis is required.（3）The impact of LNO_x on O₃ distribution over the TP has a distinct C-shaped pattern in the vertical direction.However,there are noticeable discrepancies between the northern and southern regions.In the southern portion,LNO_x primarily contributes to an increase in O₃concentration in the lower troposphere（0-6 km）whereas in the northern region,LNO_x causes an inhibitory effect on O₃ at an altitude of 10-12 km above the ground.Moreover,the increase of O₃ at the top of the troposphere is lower than that in the lower troposphere.A northward shift of the high value area is also observed.The transported LNO_x has a dominant effect on O₃alterations in the lower troposphere of the TP,which is mainly below 10 km.However,above that level in the upper troposphere and lower stratosphere（UTLS）region,the contribution of local LNO_x to the O₃ changes on the TP gradually exceeds that of the transported LNOx.This highlights the vital role played by local LNO_x in influencing O3 changes in the UTLS region of the TP.