苏州大气颗粒物PM2.5和PM10质量浓度异常“倒挂”现象的成因及影响分析

为深入研究PM_2.5和PM₁₀质量浓度异常“倒挂”现象的成因及影响，在苏州市相城区国控点开展比对监测分析，回顾性分析了2016—2020年苏州全部国控点颗粒物浓度数据。苏州市相城区国控点PM_2.5浓度的比对分析结果表明：该国控点频繁出现PM_2.5浓度高于其他国控点PM_2.5浓度和高于该站点PM₁₀浓度(“倒挂”率高达34%)的“双高”现象，PM_2.5平均浓度比其他9个国控点高12.5%～37.2%,比位于同一站点的备用监测仪器(“倒挂”率为0)高38.1%。2016—2020年，苏州全部国控点“倒挂”时间的总体趋势都是逐年递增，且集中发生在相对湿度较高的20:00至次日07:00。这5年间各国控点PM_2.5浓度异常偏高导致的异常“倒挂”现象对全市年均浓度产生的正误差分别为1.6%、2.8%、6.0%、6.2%和4.1%,基本呈现出逐年递增的趋势。上述结果表明：苏州PM_2.5浓度偏高是由动态加...

Causes of the Abnormal Reversal Between PM2.5 and PM10 Mass Concentrations and Its Impact on the PM2.5 in Suzhou

To investigate the phenomenon and impact of the abnormal reversal between PM_2.5 and PM₁₀ mass concentration,comparison monitoring and analysis was carried out at Xiangcheng District national monitoring station in Suzhou City,and the retrospective analysis for PM_2.5 and PM₁₀ data at all national monitoring stations in Suzhou from 2016 to 2020 was performed.The results showed that the PM_2.5 concentrations at Xiangcheng station were frequently higher than those at other nine monitoring stations in Suzhou City and PM₁₀ concentrations at the same station in March of 2021.As a result,the hours with higher PM_2.5 than PM₁₀ accounted for as high as 34% of the observation periods,the reversal ratio of PM_2.5 and PM₁₀ was 34%.The average PM_2.5 concentration at Xiangcheng station was higher than those at the other nine stations by 12.5%-37.2% and higher than that monitored by an instrument for comparison at the same site by 38.1%,for which the reversal ratio was 0.From 2016 to 2020,the reversal phenomenon at all national monitoring stations in Suzhou was increasing year by year,and it mainly occurred between 08 PM and 07 AM the next day when the relative humidity was high.The positive deviation resulted from the abnormally higher PM_2.5 concentrations were 1.6%,2.8%,6.0%,6.2% and 4.1% for the five years,which generally showed a continuous increase trend.These results indicated that the abnormally higher PM_2.5 concentrations in Suzhou were caused by the dynamic heating system with the inherent defect or without routine maintenance and the subsequent instability of removing moisture,which ultimately resulted in the phenomenon of the abnormal reversal of PM_2.5 and PM₁₀.The abnormal reversal of PM_2.5 and PM₁₀ and the reason beneath it are concealed to a certain extent but very widespread.Therefore,it is very necessary to pay attention to the phenomenon and take measures to prevent its impact on PM_2.5 measurement data.