| With the rapid development of industry and economy,the air quality in the Yangtze River Delta is facing great challenges,in which PM2.5(particulate matter with aerodynamic diameter less than 2.5 μm)pollution has been widely concerned.The high concentrations of PM2.5 in the atmosphere will not only cause haze and reduce visibility,but may also endanger human health,which is related to a variety of diseases.In recent years,with the progress of pollution control in China,the characteristics of pollution emissions are constantly changing,and the sources of PM2.5 have also changed.In order to control the PM2.5 pollution in the Yangtze River Delta,it is necessary to carry out new research on the source apportionment of PM2.5 in the key cities in the region.In this study,WRF-CMAQ model was used to simulate and analyze the concentration and composition of PM2.5 in 4 typical cities(Shanghai,Hangzhou,Nanjing and Hefei)in the Yangtze River Delta in January,April,July and October of 2018(representing winter,spring,summer and autumn,respectively).Combined with the ISAM source apportionment module,the contributions of different source regions and source sectors to PM2.5 and its key components of the above 4 cities were quantitatively analyzed.The verification results of the model show that the simulation results of WRF model and CMAQ model for meteorological parameters(air temperature,relative humidity and wind speed)and air pollutant concentration(PM2.5 and PM10)meet the verification standards,and the main mode of CMAQ model is consistent with the ISAM source apportionment module.The PM2.5 source apportionment results of the above 4 cities show that the largest source of PM2.5 is long-distance transport outside the Yangtze River Delta region(38.5%～52.6%)in winter,and the local emissions(43.0%～50.9%)in autumn.In spring and summer,the largest sources of PM2.5 in Shanghai,Hangzhou and Hefei are local emissions(spring:37.1%-53.3%;summer:44.1%～64.7%),while Nanjing is the transport from the surrounding areas(spring:38.5%;summer:46.3%).Among the different source sectocs in the Yangtze River Delta,the largest sources of PM2.5 in Shanghai and Hangzhou are residential sources(15.4%～23.8%and 25.0%～45.7%),while Nanjing and Hefei are industrial sources(20.2%-43.9%and 21.3%～47.5%).Due to the unfavorable meteorological conditions in winter,the concentration of PM2.5 was significantly higher than that in other seasons.Compared with the clean period,the contribution proportion of long-distance transport to PM2.5 of 4 cities decreased during the pollution period in winter,the contribution proportion of local emissions to PM2.5 of Shanghai decreased,and the contribution proportion to other cities increase,while the contribution proportion of transport from surrounding areas to the PM2.5 of the 4 cities showed an increasing trend.The components of PM2.5 include sulfate,nitrate,ammonium salt,elemental carbon,organic carbon and other components.The average annual proportion of sulfate in the PM2.5 of the 4 cities is the highest(24.5%～26.3%),while the average annual proportion of nitrate,ammonium salt,elemental carbon,organic carbon and other components is 18.9%～22.7%,14.5%～15.4%,7.2%～19.8%,9.0%～9.9%and 11.2%～24.2%,respectively.The source apportionment results of key components of PM2.5 show that the largest sources of sulfate and nitrate in Shanghai,Nanjing and Hefei are long-distance transport in winter,spring and autumn,and local emissions in summer.The largest sources of sulfate and nitrate in Hangzhou is long-distance transport in winter and local emissions in other seasons.The largest sources of ammonium salt and element carbon in the 4 cities are local emissions,the main source of organic carbon is long-distance transport in winter,and local emissions in other seasons.The results of source sectors analysis show that,when the contribution of long-distance transmission is not considered,the largest source of sulfate in Shanghai,Nanjing and Hefei is industrial source,while Hangzhou is residential source.The largest source of nitrate in Shanghai is industrial source in winter and autumn,and transportation source in spring and summer.The largest source of nitrate in Hangzhou is industrial source in winter and residential source in other seasons.The largest sources of nitrate in Nanjing and Hefei are industrial sources in all seasons.The largest source of ammonium salt in the 4 cities is agricultural source,while organic carbon is residential source.The largest source of elemental carbon in Shanghai and Hangzhou is transportation source,and the contribution of industrial source and transportation source to Nanjing is relatively close,while industrial source is the largest source of elemental carbon in Hefei. |
