Numerical Simulation And Source Analysis Of PM_2.5 And PM₁₀ Pollution Characteristics In Nanjin

With the rapid development of urbanization and industrialization,air pollution is becoming more and more serious,posing a serious threat to human health and sustainable social and economic development.Nanjing,as an important economic center in the Yangtze River Delta region of China,has a large scale of heavy industry and serious particulate pollution.It is one of the national key cities for air pollution control.Therefore,an accurate understanding of the characteristics and sources of particulate pollution in Nanjing is of great significance for scientific control of particulate pollution and effective improvement of air quality in this region.In this paper,Nanjing City is taken as the research area,and the variation characteristics of PM_2.5 and PM₁₀ mass concentration in this area are analyzed by using data from environmental monitoring stations and meteorological stations,build a localized model,and conduct numerical simulation of PM_2.5 and PM₁₀pollution by using WRF-Chem model.The high-resolution meteorological field simulated by WRF model was applied to HYSPLIT model to analyze the potential source areas of PM_2.5 and PM₁₀,the relative contribution of source areas and the pollution degree of potential source areas in Nanjing.The main research results are as follows:（1）The particulate pollution situation in Nanjing has improved.From 2018 to 2020,the concentration of PM_2.5 and PM₁₀ in Nanjing decreased year by year,and the number of days exceeding the secondary concentration limit decreased year by year.The lowest concentrations of PM_2.5 and PM₁₀ appeared in August and the highest concentrations in January.The concentrations of PM_2.5 and PM₁₀ have significant seasonal differences,showing a"one high and three low"characteristics,with the highest concentration in winter and the lowest concentration in summer.The diurnal variation curve of PM_2.5 concentration in four seasons presents a"single peak and single valley"type,while the diurnal variation curve of PM₁₀concentration presents a"single peak and two valleys"type.（2）From 2018 to 2020,the annual average concentration of PM_2.5 and PM₁₀ in Nanjing environmental monitoring stations exceeding the annual average level 2 concentration limit decreased year by year;According to the statistics of the number of days exceeding the limit in different seasons in three years,the number of days exceeding the limit of PM_2.5 and PM₁₀ in winter was the most,indicating severe pollution situation.The monthly variation trend of PM_2.5concentration in most stations presents a"U"shaped trend,while the monthly variation trend of PM₁₀ concentration in all stations presents a"W"shaped trend.（3）The concentration of PM_2.5 and PM₁₀ has a certain correlation with temperature,wind speed,relative humidity and precipitation,and is positively correlated with temperature,and negatively correlated with relative humidity,wind speed and precipitation.WRF-Chem model simulated the change characteristics of Nanjing meteorological field well,and the simulation effect of temperature was the best,followed by relative humidity and wind speed.The model can well simulate the change characteristics of the growth and attenuation of PM_2.5 and PM₁₀concentrations in Nanjing.The model overestimates the PM_2.5 concentration of each station and underestimates the PM₁₀ concentration of most stations.（4）In January,the air masses in Nanjing mainly come from the northwest and northeast directions;in April,the air mass was mainly dominated by the northwest and northeast directions;in July,the air mass was easily affected by the transport air flow from the eastern and southeastern cities;in October,the air mass was mainly affected by the northerly air flow from the north.PM_2.5 and PM₁₀ pollution in Nanjing is influenced by both local and external sources,which are mainly transported by nearby short-distance air flow and internal air flow in Jiangsu Province.In January,PM_2.5 and PM₁₀ concentrations in Nanjing were most affected by external transport,and the potential pollution contribution areas were mainly located in central Huai’an,Changzhou,Wuxi,northern Hefei and southern Chuzhou.