Analysis Of The Annual Trend Of Global Tropospheric Ozone In The Past Two Decades And Its Cause

This study combines multi-source observational data with the Earth System Model(CESM)to study the temporal and spatial distribution,interannual trend change characteristics,and seasonal change characteristics of ozone in the entire troposphere,the surface,and the free troposphere.It also explores the impact of meteorological fields,emissions,and stratospheric intrusion on stratospheric ozone.The results show that:The OMI/MLS satellite data show that the tropospheric ozone column concentration(TCO)is higher in the north than the south.During 2005-2020,,TCO in all regions except Africa has a trend of increasing,with East Asia and Southeast Asia having the strongest positive trend,Europe and Africa having the weakest positive trend.In the surface,the ozone at most regional stations in Europe has a negative trend from 2000 to 2020,and the interannual variation trend of ozone in various regions is regional due to the impact of local emissions and regional transmission.The results of EAC4 data and TOST data show that in the free troposphere,the ozone is higher in the north than the south.The ozone concentration in the low latitude area near the equator is lower,and the ozone concentration in the area of30 °N(S)～60 °N(S)is higher,among which the trend of ozone concentration in Southeast Asia from 2003 to 2020 is the most significant.The CESM2 model was used for two simulation experiments.evaluate the simulation results,the model can better reflect the spatial distribution,interdecadal variation and seasonal variation of tropospheric ozone,but the simulation results of the CESM in Southeast Asia are not ideal.The simulation results show that no matter in the whole troposphere or in the free troposphere,the emissions in most regions of the world will increase the tropospheric ozone,especially in East Asia and Southeast Asia.The change of meteorological field in the middle and high latitudes from 2000 to 2015 makes the tropospheric ozone have a negative trend,while the emission will make the ozone have a positive trend.stratospheric intrusion has a great impact on tropospheric ozone.In low latitudes near the equator,the contribution of stratospheric ozone is lower due to the high temperature and easy to generate updraft.Hadley circulation generates downdraft at 30°,making the contribution of stratospheric ozone near 30°N(S)larger.The contribution of stratospheric ozone in January and April is higher in the north than the south,The contribution of stratospheric ozone in July and October is higher in the south than the north.The reasons for the seasonal differences were mainly related to the photochemical life of ozone,the seasonal changes of Hadley circulation,the temperature and stratospheric ozone storage.In the middle and high latitudes,the change of meteorological field makes the contribution of stratospheric ozone have a negative trend from 2000 to 2020.