Analysis of PM2.5 Pollution Characteristics in Hunan Province Based on Wavelet Transform
Based on the monitoring data of PM2.5 and other five atmospheric pollutants and meteorological data in Hunan Province from 2017 to 2021,the spatial and temporal distribution characteristics of PM2.5 concentration were analyzed.The continuous wavelet transform and wavelet coherence spectrum were used to study the PM2.5 concentration cycle and the corre-lation between PM2.5 and other atmospheric pollutants and meteorological factors.The main influencing factors of PM2.5 concentration were determined.The results showed that the annual average PM2.5 concentration in Hunan Province showed a downward trend,with an average annual decline rate of 4.88％.The monthly average PM2.5 concentration showed a"U"type distribution.The highest concentration was in January 2017(91.9 μg/m3),and the lowest concentration was in June 2020(15.8 μg/m3).The spatial distribution of the annual average of PM2.5 concentration shows the characteristics of high from northeast to southwest,low from northwest to southeast,and the seasonal average of PM2.5 concentration shows the characteris-tics of winter＞autumn＞spring＞summer.There are significant periodic changes in PM2.5 concentration in 14 cities(states),mainly including a long period of about 272 days and a short period of about 36 days.The correlation between PM2.5 concentra-tion and other air pollutants is different at different time-frequency scales.There is a significant positive correlation between PM2.5 concentration and PM10 concentration at all time-frequency scales.On the hourly scale(0～64 d),PM2.5 concentration was positively correlated with O3,CO,NO2 and SO2 concentrations.On the medium time-frequency scale(64～256 d),the correla-tion between PM2.5 concentration and O3 concentration is not obvious,and there is a positive correlation with CO,NO2 and SO2 concentration.On the large time-frequency scale(256～512 d),PM2.5 concentration was negatively correlated with O3 concentration,and positively correlated with NO2 and SO2 concentration.PM2.5 concentration was positively correlated with CO concentration in Changsha and Hengyang,and negatively correlated in Huaihua.The correlation between PM2.5 concentra-tion and meteorological factors is also different at different time-frequency scales.On the hourly frequency scale,PM2.5 is negatively correlated with precipitation,relative humidity and air pressure,positively correlated with temperature and sunshine hours,and positively correlated with wind speed.On the medium-time-frequency scale,the correlation between PM2.5 and various meteorological factors is not obvious;on the large time-frequency scale,PM2.5 is negatively correlated with precipita-tion,temperature and sunshine hours,PM2.5 is positively correlated with air pressure,and the correlation between PM2.5 and rel-ative humidity and wind speed is not obvious.
PM2.5 concentrationpollution characteristicswavelet transforminfluence factorHunan Province
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