承德市降水对细颗粒物和可吸入颗粒物的清除作用分析

Scavenging effect analysis of precipitation on PM_(2.5)and PM_(10)in Chengde

利用承德市2018—2020年逐小时细颗粒物(PM_(2.5))和可吸入颗粒物(PM_(10))监测数据和气象观测资料,分析PM_(2.5)和PM_(10)基础浓度时间变化特征及不同风速影响下浓度变化规律,探讨基础浓度和风速订正后降水对污染物的湿清除作用。结果表明:(1)PM_(2.5)和PM_(10)基础浓度均值均为11月至次年3月较大,4、10月次之,5—9月较小。(2)秋、冬季风对PM_(2.5)清除效果较明显;风对PM_(10)全年总体有清除作用,但风速大于8 m/s,会导致春季PM_(10)浓度暴增。(3)降水过程对PM_(2.5)和PM_(10)均有很好的清除作用,清除率大多随着降水等级的增大而增大,降水对PM_(10)的清除率高于PM_(2.5)。(4)中雨及以上等级降水过程结束后,PM_(2.5)和PM_(10)空气质量指数均为良好及以上等级。(5)当PM_(2.5)和PM_(10)初始质量浓度高于60、110μg/m^(3)时,不同等级的降水过程均可明显降低PM_(2.5)和PM_(10)浓度。当PM_(2.5)和PM_(10)初始质量浓度低于60、110μg/m^(3)且雨强小于5 mm/h时,PM_(2.5)和PM_(10)浓度有反弹升高现象,其中当雨强小于2 mm/h时,初始浓度越低反弹的可能性越高。

Based on the hourly environmental monitoring data of PM_(2.5)and PM_(10)and the meteorological observation data in Chengde from 2018 to 2020,the time-varying characteristics of the PM_(2.5)and PM_(10)basal concentration and the change rule of concentration under the influence of different wind speeds were analyzed,and the wet scavenging effect of precipitation on pollutant were discussed after the correction of basal concentration and wind speed.The results showed that:(1)the basal concentrations of PM_(2.5)and PM_(10)were higher from November to March of the following year,followed by April and October,and lower from May to September.(2)The scavenging effect of wind on PM_(2.5)was more significant in autumn and winter.Wind had a good scavenging effect on PM_(10)throughout the year,but when the wind speed was greater than 8 m/s,the concentration would increase sharply in spring.(3)The wet scavenging rate of PM_(2.5)and PM_(10)mostly increased with the increase of the magnitude of the rainfall process,and the wet scavenging effect of PM_(10)was better than that of PM_(2.5).(4)After the process of moderate rain and above,the air quality indexes of PM_(2.5)and PM_(10)were good and above.(5)When the initial mass concentration of PM_(2.5)and PM_(10)were higher than 60,110μg/m^(3),different levels of precipitation could significantly reduce PM_(2.5)and PM_(10)concentrations.When the initial mass concentrations were lower than 60,110μg/m^(3) and the rainfall intensity was less than 5 mm/h,the mass concentration of PM_(2.5)and PM_(10)were easily rebound and increased due to hygroscopic growth.When the rainfall intensity was less than 2 mm/h,the lower the initial concentration,the higher the rebound probability.