| The temporal and spatial variations of global tropospheric ozone are analyzed by using a CAM-chem model and various ozone measurement data sets.Furthurmore,Beijing are chosed as an example to quantify the contribution of the stratospheric invasion and the tropospheric photochemical reaction to the long-term trend of tropospheric ozone over East Asia.Finally,the trend of tropospheric ozone under different greenhouse gas emission scenarios in the next 100years and its possible reasons are studied by CAM-chem model.?1?The CAM-chem model can well simulate the temporal and spatial variations of tropospheric ozone.The model results show that under the influence of ozone precursor,the high value of global tropospheric ozone are mainly located over Asia,the North Pacific and the eastern North America,and its low value is located over the Pacific Ocean.Due to the seasonal differences in the intensity of photochemical reactions,the spatial distribution of ozone is different in different seasons.There are the most significant hemispheric asymmetris of tropospheric ozone in spring and summer,and during the northern hemisphere's summer,the ozone concentrations are significantly higher than in other seasons.In the recent 30 years,the global tropospheric ozone has been basically increasing,especially in East and South Asia.From 1979 to 2003,there is the positive trend of tropospheric ozone in North America and Europe,while after 2003,tropospheric ozone remained virtually unchanged in both regions.The ozone increased region in the middle and lower troposphere was mainly located over Asia and the North Pacific,and the most significant increase in ozone is located in the upper troposphere was in Alaska in the United States,Canada and the eastern coasts of Russia.The variation of ozone in the middle and lower troposphere are basically consistent with the changes in the two precursors of CO and NOx,while the increase of ozone in the upper troposphere is closely linked to the downward transport of ozone in the stratosphere.?2?There are the significant increase of tropospheric ozone in Beijing from 2003 to 2013 and the total amount of tropospheric ozone column increases by about 0.98 DU per year.During the same period,the net transport of stratospheric ozone to the troposphere increased by about0.13×10-3 Tg0.17×10-3 Tg per year,accounting for about 20%of the increase of tropospheric ozone.The ozone change caused by horizontal transport is relatively small,increasing about 0.06×10-3 Tg per year and accounting for about 10%of the total ozone increase in the troposphere.In recent years,the amount of tropospheric ozone precursors emitted from the surface in Beijing has increased significantly,which has resulted in a significant increase in tropospheric ozone in this region.The simulation of the CAM-chem model shows that the tropospheric ozone increased about 0.53 DU per year in Beijing,and the emission of ozone precursors can contribute up about0.32 DU per year of the tropospheric ozone increase.This which accounts for about 60%of the total tropospheric ozone increase in this region.?3?The total amount of tropospheric ozone column has been increasing from 1979 to the present,but its future change will be different under different RCP emission scenarios.To be specific,the total amount of global tropospheric ozone column will decrease continuously in the future under RCP2.6 and RCP4.5 emission scenarios,and the decreasing trend of ozone under RCP2.6 is more obvious than that under RCP4.5.Under RCP8.5 emission scenario,ozone will keep its increasing trend in the future.Under different RCP scenarios,there are the different trends of several ozone precursors,and their effects on tropospheric ozone are also different.Under RCP2.6 and RCP4.5 scenarios,the decreasing trend of ozone is mainly caused by the decrease of NOx and CO emissions in the future,while under the RCP8.5 scenario,the increasing trend of tropospheric ozone is closely related to the increase of global CH4 concentration in the troposphere. |
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