| In recent years,the prevention and control of air pollution in the Guangdong-Hong KongMacao Greater Bay Area(GBA)has achieved phased results.The concentration of fine particles has been declining year by year,but the ozone concentration has continued to rise.Large-scale ozone pollution has frequently occurred.Ozone has become the primary pollutant affecting the environmental air quality in the GBA.In this context,the study of ozone in the GBA has received great attention,but the focus of the study is mainly on the near-surface ozone and its formation mechanism.There is a relatively lack of research on ozone in the vertical direction.What is the distribution of the vertical profile?What are the mechanisms affected?These studies are extremely important for the formulation of policies for the prevention and control of surface ozone,climate change,and ozone pollution.Therefore,in order to explore the vertical distribution of ozone and its influencing factors in the GBA,this study analyzed the overall situation of the vertical distribution of ozone in the GBA by using all the ozone sounding data obtained from the autumn ozone sounding observation in the GBA from 2013 to 2019 and the satellite remote sensing data of ozone monitor and microwave Limb Sounder(OMI/MLS),and explored the daily variation of the vertical distribution of ozone combined with the analysis of the daily ozone profile and difference profile of the Yangjiang.At the same time,through the analysis of the characteristics of ozone at different altitudes,the influencing factors of tropospheric ozone in Yangjiang and the formation mechanism of ozone peak and low ozone layer were more comprehensively explored.On this basis,the air quality in the GuangdongHong Kong-Macao Greater Bay Area during the Yangjiang sounding period was simulated through the Weather Research and Forecasting model and the Community Multiscale Air Quality model(WRF-CMAQ).Based on the simulation results,the effects of stratospheric ozone on GBA were quantitatively analyzed.The main conclusions are as follows:(1)From 2013 to 2019,the vertical structure of tropospheric ozone in Hong Kong in autumn showed a bimodal structure,with no significant interannual changes.The ozone peak appeared at 1 km in the lower troposphere and 8-10 km in the upper troposphere.During the period,temperature,relative humidity and CO vertical structure did not change significantly,but due to the long-term ozone pollution incident in 2019,the surface ozone concentration and the lower tropospheric ozone volume mixing ratio increased significantly in 2019.But on the whole,it did not affect the ozone concentration in the upper and middle troposphere.(2)Overall,the ozone profiles observed in Yangjiang are in accordance with those of the HKO in terms of the vertical structure.The TCO values are 34.2± 4.0 and 34.3±4.6 DU,respectively,that are,4 DU higher than those of satellite data,indicating that the OMI/MLS product underestimates the TCO level in the PRD region.The Yangjiang ozone profiles indicate significant variations in the ozone vertical structure and concentration during the observation period.A significant ozone peak permanently occurs in the lower troposphere at 1.1±0.4 km above the surface.The vertical structural difference is mainly reflected in the presence of lowozone strata(below 30 ppbv)near the tropopause and ozone peaks and high-ozone stratification in the middle and upper troposphere.The average ozone peak concentrations in the lower,middle,and upper troposphere are 65.2±9.9,57.8±7.7,71.8±13.6 ppbv,respectively,which are higher than the average ground-level ozone concentration(48.9±9.4 ppbv).(3)Based on the analysis of the profile characteristics,weather conditions,and backward trajectories,it can be concluded that the low-ozone strata near the tropopause are caused by the regional transport of the air mass from the tropical cyclone storm area.Potential vorticity analysis shows that stratosphere-troposphere exchange(STE)is the main reason for the formation of the ozone peaks and its varying concentrations in the middle and upper troposphere.Photochemical reactions represent the main factor affecting the ozone concentration in the lower troposphere.The STE is also an important factor affecting the ozone in the lower troposphere,leading to an increase in the surface ozone concentration by～10.9 ppbv.(4)WRF-CMAQ simulation results show that during the simulation period,the impact of STE on the surface ozone in the GBA is only 0.67 ppbv,with a contribution rate of about 3%.Generally speaking,it seems that the impact on surface ozone is small.However,in a single stratospheric ozone invasion event,the overall contribution of stratospheric ozone to the surface ozone concentration in the GBA exceeded 14 ppbv,and this impact lasted for a long time.Therefore,the impact of STE on the GBA cannot be ignored in terms of achieving air quality standards in the short term or in terms of long-term ecological environment management.This study reveals the characteristics of the vertical distribution of tropospheric ozone in the GBA,explores the influencing factors and related mechanisms of the vertical distribution of ozone at different altitudes,and deepens the understanding of the distribution of tropospheric ozone in the GBA.At the same time,it exposes the important impact of STE on the surface ozone concentration in the GBA,expounds the stratospheric ozone invasion mechanism in the GBA,quantifies the contribution of STE to the surface ozone concentration.This reserch provides scientific support and theoretical basis for the formulation of ozone prevention and control policies in the GBA. |
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