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

ABSTRACT

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. PM2.5 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 PM2.5, 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.