Study On Air Environmental Quality And Pollution Characteristics In Xichang City

In order to achieve the main goal of economic and social development of Xichang,improve the number of days with good air quality,ensure the high-quality development of Xichang,improve the living environment and people’s health level.Based on the ambient air quality index(PM₁₀,PM_2.5,SO₂,NO₂,CO and O₃)of xichang urban area,the temporal evolution characteristics of atmospheric AQI,the temporal evolution characteristics of atmospheric pollutant concentration,the relationship between PM_2.5 and other pollutants,the influence of special pollution events,and the regional transport characteristics of pollutants were systematically studied.The results show that:（1）The AIR quality AQI in Xichang showed a"N"shape change,with 2018 and 2019 as the cut-off point,decreasing,rising and then decreasing;The monthly fluctuation was large,the highest value was distributed in March,April,May and July,and the lowest value was distributed in August,September,October and November.The linear correlation coefficient of sites ranged from 0.592 to 0.819.The air quality grade gradually gets better,and the number of good days increases year by year.The primary pollutants on mildly polluted days are O₃and PM_2.5,the primary pollutants on moderately polluted days are PM_2.5,and the primary pollutants on severely polluted days are PM_2.5.（2）The interannual variation of pollutant in Xichang decreased firstly and then increased;The quarterly change is higher in the fourth quarter and the first quarter,and lower in the second and third quarters.Monthly changes show that pollutant in December is the highest,followed by January,February and March are slightly higher than that from April to November.All the places where the average daily change was observed were fine days from2015 to 2019,while severe pollution days and light pollution days occurred in 2020 and 2021,mainly in December 2020 and January 2021.（3）The source correlations of PM_2.5 and PM₁₀ were good,the monthly mean correlation coefficients were 0.806～0.935,and the daily mean correlation coefficients were 0.878～0.924.The monthly mean correlation coefficient was 0.302～0.510,and the daily mean correlation coefficient was 0.266～0.406.It is not related to CO,SO₂,and O₃.PM_2.5concentration is mainly affected by meteorological factors,combustion intensity,fire spreading speed,diffusion and transmission and other pollutants,but there is no significant correlation.The time,intensity and variation of PM_2.5 increase at each station are different,which are mainly affected by the wind path in Anning River Valley and Qionghai lake water area.The geographical distribution of forest fire area,air quality monitoring station and meteorological observation station is also an important influence.（4）The backward track in spring is mainly from the second type,which is from the south direction of Xichang,accounting for 45.83%;The backward track in summer was dominated by the second type,which came from the south direction of Xichang,accounting for 57.26%.The backward track of autumn is mainly the first type track,which comes from the northeast of Xichang city,accounting for 36.16%.The backward track in winter is mainly from the southwest of Xichang city,accounting for 31.32%.In spring,the main PSCF potential sources are evenly distributed,and the maximum contribution of CWT comes from northern Yunnan Province and Panzhihua City.In summer,the main PSCFs were concentrated in the local area of Xichang City,Dechang County and Miyi County of Puge County.The largest contribution of CWT was from the southern area of Xichang City,Dechang County and Yanyuan County.In autumn and winter,the distribution of main potential sources of PSCF is relatively scattered and the range is small.The maximum contribution of CWT in autumn comes from the adjacent areas of Xichang City and the northern part of Panzhihua City.The maximum contribution of CWT in winter is scattered in Xichang City,Huaping County and Yanyuan County.