Research On The Spatial And Temporal Distribution Of The Mass Concentration Of 6 Air Pollutants And The Pollution Meteorological Parameters In The Urban Agglomeration Of The Sichuan Basin

At present,the Sichuan Basin has become one of the four most heavily polluted areas in China.Air pollutants will not only change the atmospheric albedo, atmospheric condensation core,etc.,affect the local and even regional climate change,but also stimulate the human respiratory tract,enter the blood circulation adversely affect the human respiratory and cardiovascular and cerebrovascular health.Therefore,the study of the distribution of atmospheric pollutant concentration and the analysis of the meteorological parameters associated with it are very important for the reasonable control of pollution sources and the effective improvement of local air quality.In this paper,six kinds of atmospheric pollutants concentration data from 18 cities in the Sichuan Basin from 2015 to 2017 are used,as well as the orresponding weather meteorological elements and radiosonde data.The statistical methods such as concentration period,concentration degree and coefficient of ariation are used to analyze the temporal and spatial distribution characteristics of the atmospheric pollutants concentration in the Sichuan Basin.And then the elationship between the maximum mixed layer thickness of Chengdu calculated by the stepwise approximation method and the six atmospheric pollutants oncentrations was also analyzed.Three heavy pollution processes in the three years were analyzed,and a typical heavy pollution process was detailed analyzed.The ain conclusions are as follows:?1?From the point of view of the concentration of pollutants and the distribution of pollution days,in the 18 cities in the Sichuan Basin,the pollution is the most serious in Zigong,and the lightest in Guangyuan City.The distribution of pollution days during the year shows that the number of pollution days is the highest in January and the lowest in June;the number of days of pollution is the most in winter?December to February of the next year?and the least in summer?June to August?.Overall,the three regions of the Sichuan Basin are ranked according to the concentration of pollutants,the value of AQI,and the length of pollution days:Southern Sichuan Economic Zone and Chongqing>Chengdu Plain Economic Zone>Northeastern Sichuan Economic Zone.?2?During the study period,in the view of pollutants'annual average concentration among the 18 cities in the Sichuan Basin,only Guangyuan City reached the Ambient Air Quality standard for PM_2.5,and then two cities Guangyuan and Bazhong reached the standard for PM₁₀.For SO₂,all of the cities reached the standard,and for NO₂except Chengdu and Chongqing,the other 16 cities were all up to standard.See from the daily concentration of CO,all of the 18 cities reached the standard.Judging from the long-term trend of interannual change,the concentrations of particulate matter and SO₂ have been reduced to some extent in the past 37 years,indicating that the state's control of air pollutant emissions is very significant in effectively improving urban air quality.?3?The six kinds of atmospheric pollutants have obvious seasonal characteristics.The seasonal mean values of PM_2.5,PM₁₀,NO₂,and SO₂ concentrations are winter>spring>autumn>summer,and the seasonal mean of CO is winter>autumn>spring>summer,while the concentration of O₃ on the contrary shows lower in winter but higher in summer.In terms of the concentration degree,the pollutants PM_2.5,PM₁₀and O₃ are much more concentrated than SO₂,NO₂ and CO,and for the concentration period,the pollutants PM_2.5,PM₁₀,SO₂,NO₂ and CO are mainly concentrated in January,while the O₃ is mainly concentrated in June and around the summer.In these two periods,efforts should be made to deal with the prevention and control of atmospheric pollutants.From the perspective of the inter-city differences in atmospheric pollutants,the differences in SO₂ and NO₂ concentrations in different cities are more obvious,and the distribution of other air pollutants in different cities is relatively uniform.?4?By analyzing the characteristics of the maximum mixed layer thickness in Chengdu during the period from 2015 to 2017 and its correlation with six kinds of atmospheric pollutants,it can be known that the highest monthly maximum mixed layer thickness in Chengdu appears in May,the lowest is in December.From the seasonal average,the highest maximum mixed layer thickness is in spring,followed by summer,the difference between autumn and winter is minimal,showing the lowest.The spring is also the season with the highest frequency of the largest mixed layer thickness above 2000m in Chengdu,while the season with the highest frequency of the largest mixed layer thickness less than 2000m is autumn.From the analysis of the correlation between the pollution concentration and the thickness of the mixed layer,the correlation between the concentration of contaminants and the maximum mixed layer at 14 o'clock was better than the correlation between the daily average concentration and the daytime concentration with the maximum mixed layer thickness.The positive correlation between the concentration of O₃ and O₃-8H at 14o'clock with the maximum mixed layer thickness?respectively R=0.648,P=0.001;R=0.655,P=0.001?and the negative correlation between the concentration of NO₂and CO with it?R=-0.497,P=0.001;R=-0.476,P=0.001?are all very significant.But the negative correlation between AQI,the concentration of PM_2.5,PM₁₀,and SO₂with the maximum mixed layer thickness?respectively,R=-0.199,P=0.05;R=-0.301,P=0.05;R=-0.224,P=0.05;R=-0.208,P=0.05?is more significant.In summary,the mixed layer thickness in the spring of the Sichuan Basin is more conducive to the dilution and diffusion of atmospheric pollutants,while autumn and winter are not conducive to dilution and diffusion of atmospheric pollutants.?5?Through the statistical analysis of the heavy pollution process in the Sichuan Basin from 2015 to 2017,three more serious pollution processes were identified.The first pollution process was from January 1,2015 to January 27,2015,the second pollution process from December 25,2015 to January 6,2016 and the third pollution process from January 1,2017 to January 29,2017.From the analysis of the pollution processes,we can see that the most polluted cities in the heavy pollution processes are Zigong,Chengdu,Meishan,Dazhou,and Yibin.From the spatial distribution point of view,the more polluted cities are mainly located in the southwest of the south Sichuan zone and chongqing and the middle and south of the Chengdu plain economic zone.The six kinds of atmospheric pollutants whose concentration in the process of heavy pollution in 2017 is more consistent with the change of AQI is PM_2.5,PM₁₀0 and CO,but the concentration of other three kinds of pollutants is weak or not obvious.From the perspective of meteorological conditions,500hPa was mainly affected by the weak weather system during heavy pollution period,and there was a significant negative correlation between daily precipitation and daily average concentration.