北京市典型区域夏季降水及其对大气污染物的影响

通过采集北京市典型区域2015年夏季大气降水样品,分析研究了大气降水的理化特性,典型降水过程化学组分的变化特征、成因以及对大气污染物的影响.结果表明,北京市典型区域夏季降水pH值范围为5.15~7.34,雨量加权平均值为6.21,酸雨率极低.降水中污染元素Cd、Ca和Mn呈现中度富集,Cu、Zn、Pb和S呈现严重富集;Ca和S是降水中主要污染元素,分别占总污染元素浓度的45.43%和43.93%,Zn、Mn、Cu、Pb和Cd是降水中主要重金属污染元素,占总污染元素浓度的1.32%.降水速率不同的降水对大气污染物的影响作用也有所不同.降水速率较大的降水对PM_(2.5)的清除作用较小,对SO_2、NO_2和O_3的清除作用较大,且影响机制表现为4个重要过程:大气污染物的清除、累积、累积和清除、清除.降水速率较小的降水主要以云内雨除为主,对PM_(2.5)、SO_2、NO_2和O_3的云下清除作用较小,且影响机制表现为:污染物的清除、清除和累积、累积、以及清除为特征的4个重要过程.降水速率较大的降水对大气污染物的清除作用大于降水速率较小的降水.

Precipitation and Its Effects on Atmospheric Pollutants in a Representative Region of Beijing in Summer

Atmospheric precipitation samples were collected in a representative region of Beijing in summer of 2015 to investigate the physical and chemical characteristics of atmospheric precipitation, the changes and causes of major chemical components in rainwater during the course of typical precipitation, and the impacts of typical precipitation processes on atmospheric pollutants. The volume-weighted mean pH value of rainwater in the representative region of Beijing in summer was 6.21 with the range of 5.15-7.34,and acid rain seldom occurred. The pollution elements Cd, Ca and Mn were moderately enriched, and Cu, Zn, Pb and S were seriously enriched in rainwater, of which Ca and S were main pollution elements, which accounted for 45.43% and 43.93% of the total pollution elements respectively, and Zn, Mn, Cu, Pb and Cd were main heavy metal pollution elements, which accounted for 1.32% of the total pollution elements. Different rates of precipitations could have different impacts on atmospheric pollutants. PM_2.5 could be scavenged by raindrop, and SO₂, NO₂ and O₃ could be scavenged greatly by raindrop during the precipitation episode at a relatively high rainfall rate, containing four significant stages, such as clear-out of atmospheric pollutants, accumulation, both accumulation and clear-out, and another clear-out of airborne pollutants. Atmospheric pollutants such as PM_2.5, SO₂, NO₂ and O₃ could mainly be scavenged by in-cloud scavenging processes during the precipitation episode at a relatively low rainfall rate, including four important stages, such as clear-out, both clear-out and accumulation, accumulation, and another clear-out of atmospheric pollutants. The effect of rainfall at a relatively high rate on atmospheric pollutants was bigger than that of rainfall at a relatively low rate.