Spatio-temporal Characteristics Of PM_2.5 And Correlation Analysis Of Atmospheric Composite Pollutants In Winter In The Yangtze River Delta

Since 2013,the state has carried out routine monitoring of PM2.5 in the whole country,which has accumulated massive air quality monitoring data and lay the foundation for the analysis of PM2.5 pollution characteristics based on long time series systematically.Utilizing the PM2.5 and PM10,CO,SO2 and NO2 per hour average concentration data of 162 air quality automatic monitoring stations in 2013?2016 winter(November to February)in Yangtze river delta region,we have analyzed the time and space distribution characteristics of PM2.5,and the correlation among PM2.5 and the four other pollutants during the process of compound air pollution.The main research contents include:(1)The massive air quality monitoring data in the whole Yangtze river delta is screened and preprocessed,and the PM2.5 concentration under different time scales is accounted and calculated.(2)The PM2.5 concentration over time is analyzed with the seasonal average,monthly average and daily average data of PM2.5 concentration in the Yangtze river delta region.For each monitoring site,the PM2.5 concentration of the season and the monthly mean value is interpolated suing the kriging space method,in order to calculate the spatial distribution and variation characteristics of PM2.5 concentration;utilizing the global Moran's I index and local G index,the global correlation and local agglomeration of PM2.5 concentration in the Yangtze river delta region are studied.(3)The multiple linear regression model of the relation among PM2.5,PM10,CO,SO2 and NO2 concentration is established in order to evaluate the correlation among the five pollutants,and the effects of the concentration variation of the four other pollutants on PM2.5 is analyzed.(4)The Association rule mining method is applied to analyze the correlation between PM2.5 and other atmospheric pollutants,the association rules mining scheme is designed,he strong association rules of PM2.5 in different pollution levels is identified,in order to study the relationship among different levels of pollutants during the process of atmospheric compound pollution.The conclusions are drawn as follows through the study above:(1)Temporal change characteristics of PM2.5 concentration.The quarterly mean densities of the PM2.5 in the region from 2013 to 2016 in winter(from November to February next year)are 92.92?g/m3,76.02?g/m3,68.42?g/m3 and 56.6?g/m3 and the over-standard rates(2013?2016)of the concentration per hour of PM2.5 are 50.21%42.10%?33.92%and 27.51%.The seasonal mean density and over-standard rate of PM2.5 show a declining tendency year by year.The monthly mean densities in November,December,January and February in four winters are 68.67?g/m3,81.73?g/m3,79.81?g/m3and 66.97?g/m3 respectively,and they ranks as follows:the density in December the first,that of January second,November third,and February fourth,which makes the monthly density an inverted "U" type periodic change.And the daily average concentration shows an inverted "U" type of periodic pulse with a cycle about 6 days.(2)The spatial distribution of the concentration of PM2.5 in winter from 2013 to 2016 in the Yangtze River Delta region shows a ladder-like gradual decline from north to south,and it also shows some much higher concentrations in some areas.The distribution of PM2.5 concentration in the whole area shows significant positive correlation,and the concentration of PM2.5 in some spots shows an obvious aggregation.The higher concentration of PM2.5 is mainly located in Xuzhou,Suqian and Changzhou in the north of Jiangsu Province.The low concentration of PM2.5 is mainly located in Zhoushan,Lishui,Ningbo and Wenzhou in the southeast of Zhejiang Province.Monthly PM2.5 concentration shows similar spatial aggregation in winter.In Zhejiang Province,Jiangsu Province and Shanghai,the concentration of PM2.5 in Jiangsu Province is the highest,and the concentrations of PM2.5 in Zhejiang and Shanghai are similar.There is a synergism in the monthly PM2.5 concentrations of Shanghai,Zhejiang and Jiangsu.(3)PM2.5 shows a significant positive correlation with PM10,SO2,NO2 and CO,and their correlation coefficients are 0.742,0.457,0.501 and 0.665 respectively.By the regression equation,it is found that when any of the four pollutants in PM10,SO2,NO2 and CO increase by one unit density while other 3 remain the same,the concentration of PM2.5 increases by 0.326 unit,0.198 unit,0.131 unit and 0.027 unit.(4)PM2.5 has the strongest association with PMio:when PM10 reaches Level 4,70.13%of PM2.5 reaches Level 5,and when PM10 reaches Level 6,81.65%of PM2.5 reaches Level 6.Any one among SO2,NO2,CO reaches Level 3,the possibility that PM2.5 reaches Level 6 rises to 90%.When the high concentration of NO2 occurs,the probability of the PM2.5=Level 5 is greater than the that of the PM2.5=Level 6,that is,the high concentration of NO2 coexists with the Level 5-PM2.5 in the atmosphere.