成都市降水对大气污染物的清除效果分析

成都市受特殊地形和气候条件影响，地面风速小，静风比例高，空气湿度大，大气污染物扩散缓慢，主要靠降水的冲刷和清除作用去除大气污染物.利用2014年5月13日-2017年12月31日成都市逐小时ρ（PM_2.5）、ρ（PM₁₀）、ρ（NO₂）、ρ（O₃）、ρ（CO）、ρ（SO₂）监测数据和同期地面降水量观测数据，分析了降水前污染物质量浓度、小时最大降水量、降水持续时间及累积降水量对大气污染物清除效果的影响.结果表明:①降水对6种大气污染物的清除率随降水前污染物质量浓度的增加而增大，并且汛期降水对大气污染物的清除率大于非汛期降水.②降水对大气污染物起正清除作用，清除率随降水持续时间的增加而增大.③不同降水量对不同污染物的清除效果不同，对PM_2.5、PM₁₀、NO₂、CO和SO₂的清除率随降水量的增加而逐渐增大，对O₃的清除效果相差不大且清除率均较大；小时最大降水量对PM_2.5、PM₁₀、NO₂、O₃、CO、SO₂的清除率平均值分别为29.48%、26.95%、22.02%、26.87%、11.94%、28.75%，累积降水量的清除率平均值分别为31.64%、30.66%、24.38%、26.31%、13.89%、32.91%，其中CO不易溶于水，降水对其清除作用明显小于其他几种污染物.研究显示，降水对大气污染物的清除作用显著，对SO₂、PM_2.5和PM₁₀的清除效果较好，而对CO的清除效果较差. 

Scavenging Effect of Precipitation on Removal of Atmospheric Pollutants in Chengdu City

Due to its special topography and climate conditions, Chengdu City is characterized by low surface wind speed, high proportion of calm wind, and high air humidity, which do not favor rapid diffusion of atmospheric pollutants. Atmospheric pollutants are mainly removed by the scavenging effect of precipitation. Based on the hourly air pollutant concentration (PM_2.5, PM₁₀, NO₂, O₃,CO and SO₂) data of Chengdu City from May 13^th, 2014 to December 31^st, 2017 simultaneous precipitation data, the scavenging effects of precipitation on the removal of atmospheric pollutants are analyzed according to pollutant concentration before precipitation, maximum hourly rainfall, rainfall duration and cumulative rainfall. The results showed that:(1) The scavenging effects of precipitation on the removal of atmospheric pollutants increased with the increase of pollutant concentration before precipitation, and were higher in the rainy season than that in the non-rainy season. (2) Precipitation played a positive role in the removal of atmospheric pollutants, and the scavenging effects increased with the increase of rainfall duration. (3) Moreover, different amount of precipitation had different removal efficiency for different pollutants. The scavenging effects of PM_2.5, PM₁₀, NO₂, CO and SO₂ were increased with the increase of amount of precipitation. However, O₃ concentration was almost the same in different amount of precipitation and it was always high. The mean scavenging effects of maximum hourly rainfall to PM_2.5, PM₁₀, NO₂, O₃, CO and SO₂ were 29.48%, 26.95%, 22.02%, 26.87%, 11.94%, 28.75% respectively, and the mean scavenging effects of cumulative rainfall were 31.64%, 30.66%, 24.38%, 26.31%, 13.89%, 32.91% respectively. The scavenging effects of CO was less than that of other pollutants because of its low solubility in water. In conclusion, the scavenging effects of precipitation on the removal of atmospheric pollutants were obvious, which were better on the removal of SO₂, PM_2.5 and PM₁₀ than other atmospheric pollutants, and the rainfall had less scavenging effect on CO.