降水对江浙沪PM2.5的清除效率研究

Analysis on scavenging effect of precipitation on PM2.5 in Jiangsu, Zhejiang and Shanghai area

为了解不同程度的降水对江浙沪地区大气PM 2.5 的清除作用,搜集了2014—2016年该地区41个城市的降水和PM 2.5 观测数据,通过对比 2 a 非降水和全时段PM 2.5 平均浓度的差异,发现前者显著高于后者,说明降水对该地区PM 2.5 具有清除作用。利用降水前与降水期间PM 2.5 的浓度差异作为降水对PM 2.5 的清除率,降水后与降水期间的浓度差异作为雨后浓度回升的增加率,分别研究了目标区域不同时期、不同降雨量以及不同降雨时长对PM 2.5 的清除效果。结果显示:(1)与江浙沪南部地区不同的是,北部地区降水清除率与降水前浓度存在正相关,降水后浓度的增加与当地的排放量呈正相关。(2)当降水量为30 mm或者降水时长为 36 h 时,清除率增幅减缓,说明降水对PM 2.5 的清除效率存在着阈值。

To understand the scavenging effect of precipitation on PM 2.5 in Jiangsu-Zhejiang-Shanghai area, the precipitation and PM 2.5 observation data from 2014 to 2016 in 41 cities were analyzed. By comparing with the average concentrations of PM 2.5 between non-precipitation and full-time in two years, it is found that the former was significantly higher than the latter, showing that precipitation has a scavenging effect on PM 2.5 in this area. The ratio of PM 2.5 concentration before and after precipitation was used as the scavenging rate, while the ratio of concentration after precipitation and precipitation was used as the increasing rate. We studied the scavenging efficiencies of PM 2.5 at different periods, precipitations and precipitation durations in the target area. The results show that:(1) there is a positive correlation between scavenging ratio and pre-precipitation concentration of PM 2.5 in the northern part of Jiangsu-Zhejiang-Shanghai area, and the concentration of after precipitation are positively correlated with local emissions, which are different from the southern part of Jiangsu-Zhejiang-Shanghai area.(2) When the precipitation is 30 mm or the duration of precipitation is 36 h, the increase rate of the scavenging slows down, indicating that there is a threshold value for the PM 2.5 scavenging efficiency by precipitation.