降水对四川盆地细颗粒物的清除作用分析

Scavenging Effect of Precipitation on Removal of Fine Particles in Sichuan Basin

利用2016-2019年四川盆地内成都、乐山、宜宾、绵阳和达州5个典型城市的逐小时PM_(2.5)环境监测数据和降水、风速等地面气象台站资料,分析了降水对细颗粒物清除率的影响。结果表明:降水对细颗粒物有一定的清除作用,清除率与降水过程的累积雨量、雨强、持续时间和地面风速等密切相关。四川盆地内,当雨强低于1 mm/h,降水过程累积雨量低于1 mm时,对PM_(2.5)的清除作用有限,随着雨量的增加,清除率明显提高。小雨、中雨和大雨的平均清除率分别为17%~22%、31%~37%和32%~50%。约30%~45%的小雨量级降水出现后,PM_(2.5)浓度升高,中雨和大雨量级降水出现后,PM_(2.5)浓度升高率明显低于小雨的。当降水过程持续时间小于1 h时,降水对PM_(2.5)的清除效果不明显;持续时间大于6 h,清除效果显著提高。盆地大部分降水过程地面风速较小,但风速对PM_(2.5)浓度的清除率具有明显作用。降水过程前和过程中的风速越大,平均清除率越高,且小雨过程中因风速增加产生的消除作用大于中雨和大雨过程中风速增加产生的消除作用。

Based on the hourly PM_(2.5) environmental monitoring data and meteorological data(such as precipitation and wind speed)from surface stations of five typical cities(Chengdu,Leshan,Yibin,Mianyang and Dazhou)in Sichuan Basin from 2016 to 2019,the scavenging effect of precipitation process on removal of fine particulate matter is analyzed in this paper.The results show that precipitation has a certain scavenging effect on fine particles,and the removal rate is closely related to the accumulated rainfall,the rainfall intensity and duration,and the surface wind speed in the precipitation process.In Sichuan Basin,when rainfall intensity is less than 1 mm/h,and the accumulated rainfall is less than 1 mm,the scavenging effect of precipitation on PM_(2.5) is limited.As the rainfall increases,the removal rate increases significantly.The average removal rates of light,moderate and heavy rain are 17%22%,31%37%and 32%50%,respectively.After the occurrence of about 30%45%light rain,PM_(2.5) concentration increases,and after the occurrence of moderate and heavy rain,PM_(2.5) concentration becomes significantly lower than that of light rain.When the rainfall duration is shorter than 1 h,the scavenging effect of precipitation on PM_(2.5) is not obvious,but when the rainfall duration exceeds 6 h,the removal rate increases obviously.The surface wind speed in most precipitation processes in Sichuan Basin is small,but the wind speed has a considerable effect on the removal rate of PM_(2.5) concentration.The greater the wind speed before and during the precipitation process,the higher the average removal rate.Moreover,the increase of wind speed in light rain process has a much greater effect on the removal of PM_(2.5) concentration than that in moderate and heavy rain processes.