Analysis Of Elevated Ozone Formation Mechanism And Radiative Effect During Heat Waves In Yangtze River Delta

Under the background of global warming,heat wave accompanied with elevated ozone becomes more frequent in most part of the world,which have significant influence on human health,ecosystems and climate change.With' rapideconomy development andacceleration of urbanization process,heat waves as well as ozone pollution becomeoutstandingin Yangtze River Delta(YRD).Investigation on tropospheric ozone under high.temperature will be beneficial to reveal enhancedozoneformation and its radiation feedback on.climate change.In this paper,combined with observational data diagnosis.and numerical simulation,characteristics of surface ozone and air temperatureare analyzed over YRDfirstly.Then explore the main process of high ozone formation during heat waves with a regional climate model RegCM-CHEM4.Finally,investigate the radiation effect of elevated tropospheric ozone on climate change by improving the model.Following are the main results of this study.Firstly,analysis of surfaceozone and air temperature changes based on observationaldata between the years of 2013and2016 in YRD.Results show that intypical cities of YRD,daily variation of ozone characterized by a single peak,when peak value appears at about 3pm local time.Averaged ozone concentration during summer of YRD is 31.7±20.3 ppb,slightly higher than the background valuein the northern hemisphere.The growth rates for Shanghai,Nanjing,Hangzhou and Hefei are +0.06 ppb yr-1,+2.31 ppb yr-1,+0.25 ppb yr-1 and +1.58 ppb yr-1,respectively.2-m temperature observational data show that the year of 2013 and 2016 are twotypical heat wave years,with maximum temperature up to 41?,and high temperature weather throughout the summer accounted for 47.3%and 27%respectively.Ozone concentration has a good positive correlation with temperature and ozone exhibits different growth rates at different temperature episodes,which found to increase at a rate of 4-5 ppb K-1 within the temperature range of 28-38?,but decrease under extremely high temperature.Secondly,regional climate model RegCM-CHEM4 is evaluated by EIN15 reanalysis data and observationalozone data andthen the main formation process of high ozoneis exploredby selection of typical heat wave and non-heat wave episodes.Results demonstrate RegCM-CHEM4 can simulate the main characteristics of meteorological field and the concentration of ozone pollutants in China.Case study of heat wave and non-heat wave showed that there is a good spatial correlation between high temperature and high ozone,and high value are mainly concentrated in the North China Plain,TRD and Sichuan Basin.The difference of ozone value between two cases is as large as 45 ppb.Process analysis find that chemical reactions play the most important role in ozone formation during heat.wave days,which result in 12 ppb ozone enhancement compared to non-heat wave days.Chemical formation of ozone can be influenced by several factors.During heat waves,a more stagnant condition,controlled by anti-cyclone with sink airflow,lead to less water vapor in YRD from south and contribute to less cloud cover,which favor a strong solar radiation environment and ozone significantly increasing.High temperature also slightly promote the effect of vertical turbulence and horizontal advection,which beneficial to ozone remove,but the magnitude is much smaller than chemical effect.Finally,investigate the radiation effect of tropospheric ozoneduring summer of 2013 through improvement of the radiation transmission scheme in the regional climate chemistry model RegCM-CHEM4.Ozone data from chemical module is used to replace the climate ozone profile in the radiation module,and find that compared with climate ozone,model simulated higher value focused in boundary layer.The averaged elevating ozonebetween two cases is 4.85 ppb,3.29 ppb and 3.92 ppb in June,July and August,respectively,and column concentrationincreasedby 1.05 DU,0.580 DU and 0.726 DU,below 750 hPa.As ozone increased,more long-wave radiation is absorbed,which lead to averaged long-wave radiation flux reduction by-0.033 W m-2 at the top of atmosphere· And at the same time,increased ozone emit long-wave radiation contributing more long-wave radiation flux by 0.063 W m-2 at surface.The change of the radiation flux directly leads to the change of temperature by 0.04? DU-1,and increasing ozone can also decrease cloud cover,increase sensible heat flux and boundary layer,but the change is relatively small.