北京城区降水对PM2.5和PM10清除作用分析

基于北京市PM_2.5和PM₁₀质量浓度、组分浓度以及降水数据，利用数理统计、相关性分析等方法分别从降水总量、降水时长和降水前颗粒物浓度3个角度研究降水对PM_2.5、PM₁₀的清除作用，同时以一次典型降水过程为例，具体分析降水对颗粒物的影响。结果表明：降水总量的增加有助于促进PM_2.5、PM₁₀的清除，随着降水总量增加，PM_2.5、PM₁₀的平均清除率提高，有效清除的比例增加；连续降水可增强对大气颗粒物的湿清除作用，连续降水达3d可有效降低PM_2.5、PM₁₀浓度；降水对PM_2.5、PM₁₀浓度的清除率和大气颗粒物前一日的平均浓度有较好的正相关性。降水对大气颗粒物的清除可分为清除、回升和平稳3个阶段，各个阶段大气颗粒物的变化趋势不同。降水对于大气气溶胶化学组分和酸碱性的改变具有明显作用，对于大气颗粒物各种组分的清除效果不完全相同。对于大气中OC、NO₃^-、SO₄^2-和NH₄⁺去除率较高，且这4种组分主要以颗粒态形式被冲刷进入降水中，加剧了北京市降水酸化程度。

Effects of Precipitation on the Removal of PM2.5 and PM10 in Beijing Urban Area

Based on the data of PM_2.5,PM₁₀ mass concentration,component concentration,as well as precipitation in Beijing,this study studies the clearing effect of precipitation on PM_2.5 and PM₁₀ from three aspects of total precipitation,precipitation duration and particle concentration before precipitation,using mathematical statistics,correlation analysis and other methods. At the same time,a typical precipitation process is taken as an example to specifically analyze the impact of precipitation on particulate matter. The results show that: The increase in total precipitation helps promote the removal of PM_2.5 and PM₁₀. With the increase in total precipitation,the average removal rate of PM_2.5 and PM₁₀ increases,and the proportion of effective removal increases. Continuous precipitation can enhance the wet removal of atmospheric particles,and continuous precipitation for three days can effectively reduce the concentration of PM_2.5 and PM₁₀.The removal rate of PM_2.5 and PM₁₀ for precipitation has a good positive correlation with the average concentration of atmospheric particles in the previous day. The removal of atmospheric particulate matter by precipitation can be divided into three stages:Removal,recovery and stability. The change trend of atmospheric particulate pollutants varies in each stage. Precipitation has obvious effect on the change of chemical composition and acid-base property of atmospheric aerosols,and the removal effect of various components of atmospheric particles is not exactly the same: Precipitation has a high removal rate of OC,NO₃^-,SO₄^2- and NH₄⁺ in the atmosphere,and these four components mainly exist in the form of particles and are washed into the precipitation,which exacerbates the acidification of precipitation in Beijing.