常熟市秋冬季典型大气重污染过程中PM2.5及其主要化学组分分析

利用2018-11-21—12-05常熟市空气质量自动监测站点的常规参数逐时数据、细颗粒物化学组分数据及大气颗粒物激光雷达监测结果，对常熟地区秋冬季一次重污染过程中PM_2.5及其主要化学组分（水溶性离子）的污染特征进行系统分析。结果表明:11-24—12-03常熟地区出现了一次持续重污染过程，PM_2.5浓度高值主要出现于高湿、小风、低边界层的天气条件下，且PM_2.5浓度与湿度呈显著正相关，受不利扩散条件下的局地污染累积及高湿状态下颗粒物二次转化影响较大。观测期间，二次离子（NO₃-、NH₄+、SO₄2-）在水溶性离子中占比较高，尤其是污染期，占比高达97%，受二次生成影响较大；其中，NO₃-在水溶性离子中占比最高。整个分析时段，SOR与NOR均值分别为0.38与0.22，污染期间SOR与NOR均值明显升高，分别达到0.47与0.32；4个阶段内仅有污染期时段的NO₃-、SO₄2-累积增长速率大于CO，此时NO₃->SO₄2-，该阶段主要受到NO₂二次转化影响，常熟市重污染期间应着重加强工业源与移动源的管控。

ANALYZE ON PM2.5 AND ITS MAIN CHEMICAL COMPOSITION DURING TYPICAL HEAVY AIR POLLUTION IN AUTUMN AND WINTER IN CHANGSHU

Based on the hourly data provided by Changshu Environmental Monitoring Station and chemical composition data of PM_2.5 and lidar monitoring data from November 21st to December 5th in 2018, the pollution characteristics of PM_2.5 and its main chemical composition (water-soluble ions) in a heavy pollution process in Changshu were systematically analyzed. The results showed that Changshu occurred a continuous heavy pollution process from November 24th to December 3rd, the high PM_2.5 concentration mainly occured in higher humidity, lower wind and lower boundary layer weather conditions, and the PM_2.5 concentration was positively correlated with humidity. Accumulation of local pollution under adverse diffusion condition, the increase of moisture absorption of particulate matter under high humidity conditions and secondary transformation were the main causes of pollution. During the observation period, secondary ions(NO₃-、NH₄+、SO₄2-)accounted for a higher proportion (as high as 97%) of water-soluble ions, especially in the pollution period, which was greatly affected by secondary formation, and NO₃- accounted for the highest proportion of water-soluble ions. During the whole analysis period, the mean values of SOR and NOR were 0.38 and 0.22, and the values increased significantly during the pollution period, reaching 0.47 and 0.32, respectively. The cumulative growth rates of NO₃-, SO₄2- were higher than those of CO only in the pollution period, and the concentration of NO₃- was higher than SO₄2-, which indicated the pollution was mainly affected by the secondary generation of NO₂. It was necessary to strengthen the control of industrial emission sources and motor vehicle exhaust sources during heavy pollution period.