Spatial-Temporal Characteristics of Air Quality in Chengdu during 2015 and 2022
Based on the hourly data of Chengdu air quality index(AQI)and air pollutant mass concentration in 2015-2022,the tem-poral variation characteristics of air quality and pollutant mass concentration in Chengdu were analyzed by mathematical statistics,the spatial distribution characteristics of PM2.5 and PM10 of major pollutants were analyzed by Kriging interpolation,and the correla-tion between air quality index and pollutant concentration was explored by Pearson correlation analysis.The results showed that:(1)The air quality in Chengdu in 2015-2022 was mainly good,the annual average value of AQI was 73,the interannual change rate was 34%,showing a trend of decreasing year by year,the monthly fluctuation of AQI was significant,the maximum monthly aver-age value 120 appeared in January,and the minimum value 45 appeared in September.(2)The annual average mass concentration of PM2.5,PM10,SO2,NO2 and CO gradually decreased,the monthly average mass concentration showed a"U"shaped change trend,the monthly average maximum value appeared in December or January of the following year,the annual average mass concentration of O3 fluctuated and increased year by year,and the monthly average mass concentration showed a trend of bimodal structure.The maximum occured in May and July.(3)The primary pollutants in Chengdu were mainly PM2.5 and PM10,with a cumulative annual occurrence of 1 285 days and 522 days,respectively.They had a higher frequency in winter,with the occurrence frequency of 1,598 days and 73 days,accounting for 46.5%and 14%of the occurrence days,respectively.NO2 occurred in 689 days,with a high frequency in summer and autumn.The number of days exceeding the standard with SO2 and CO as the primary pollutants was 0d.(4)AQI generally showed the spatial distribution characteristics of high in the middle and low in the surrounding area,and the dis-tribution of pollutant concentration had obvious spatial differences.The spatial distribution of PM2.5 and O3 was characterized by a gradual increase from northeast to southwest;PM10,CO and NO2 gradually expands from the central to the periphery,and SO2 gradu-ally decreases from north to south,and a high-value center appears in the central part.(5)PM2.5 is the main air particulate pollution,and AQI is significantly positively correlated with PM2.5,PM10,NO2,SO2 and CO,and negatively correlated wity O3.PM2.5 and PM10 have a greater effect on AQI.