Study On The Impact Of High Temperature Suppression On Ozone Pollution In The Yangtze River Delta Region: Analysis Of Pollution Mechanism And Application Of Statistical Forecastin

With the development of urbanization and industrialization,China is facing an increasingly serious ozone pollution problem.Meteorological conditions are important factors affecting ozone pollution,where meteorological factors such as temperature,radiation,humidity,and boundary layer height are closely related to the level of ozone concentration.In general,temperature is significantly and positively correlated with ozone concentration,and changes in temperature lead to changes in atmospheric oxidation capacity,which in turn affects the photochemical production of ozone.However,when the temperature exceeds a certain threshold,the growth trend of ozone concentration will gradually become slower or even decrease,i.e.,the phenomenon of high temperature ozone suppression.With the frequent occurrence of high temperature events in recent years,it is important to study the characteristics and mechanisms of high temperature ozone suppression.In this paper,the meteorological conditions and ozone pollution in the Yangtze River Delta region from 2016 to 2020 is analyzed,the characteristics of ozone suppression phenomenon are diagnosed,the formation mechanism and influencing factors are explored,and further,the high temperature ozone suppression mechanism is combined with machine learning models to improve the accuracy of ozone concentration prediction models.The main conclusions are as follows.From 2016 to 2020,the ozone concentration in the YRD showed a fluctuating rise,with April to June and September to October being the months of high ozone value,and the ozone concentration in northern cities was higher than that in southern cities.Ozone was positively correlated with temperature and boundary layer height,and negatively correlated with humidity in the YRD.Ozone had the highest probability of exceeding the standard when the dominant wind direction was easterly,the temperature was 35-40℃,the humidity was 30%-40%,and the boundary layer height was 1500-2500m.Ozone suppression occured when average daytime temperature reached 30℃(the cutoff temperature)in the YRD,and the cutoff temperature varied slightly from city to city.The main meteorological causes of high temperatrue ozone suppression in the YRD include:1)The relative humidity of high temperature days in the YRD was higher,generally more than 60%,high humidity controled the surface ozone pollution by increasing the absorption of solar radiation and enhancing the absorption of ozone by aerosol and plants.2)The boundary layer height increased significantly in high temperature days,the dilution of atmosphere mixing processed was over the effect of vertical transport also contributed to ozone depletion when boundary layer height exceeded 1600m.Overall,in the high temperature days,the ozone concentration decreased by 15.3%compared with other time in summer in the YRD.Furthermore,the combined models of Random Forest,XGBoost,Support Vector Machine and BPNN were used to predict ozone concentration,and the improvement of high temperature ozone suppression mechanism was compared.The results show that the prediction accuracy of the optimized Random Forest,XGBoost and Support Vector Machine improve by 1.3%,2.5%and10.2%,respectively,and MAE decrease by 3.1%,8.4%and 8.0%,respectively.The combined models of XGBoost and Random Forest can well predict the ozone concentration in the YRD,and the R~2 is 0.83 and 0.80,respectively.This paper provides data support and scientific reference for ozone pollution mechanism research and model prediction.