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华北平原大气污染与低能见度状况一直是人们关切的问题.本文通过分析2014-2017年PM2.5化学成分的浓度和消光效果,研究了华北平原典型城市保定市的大气污染特征.结果表明,PM2.5组分的年均浓度显示下降趋势,水溶性无机离子,碳质气溶胶和金属元素分别减少了11 μg m-3,23μgm-3和1796 ng m-3.NH4+,NO3-和SO42-是PM2.5污染的主要污染物,三者之和占总离子浓度的82.9％.基于IMPROVE方程对细颗粒物进行重构,在观测期间PM2.5质量浓度平均为93±69μgm-3,春季,夏季,秋季和冬季的消光系数分别为373.8±233.6 M m-1,405.3±300.1 M m-1,554.3±378.2 M m-1和1005.2±750.3 M m-1.硫酸铵,硝酸铵和有机物对消光的贡献最大,不同季节下占比达55％～77％.通过PM2.5组分进行重构,利用IMPROVE算法计算得到Rbsca,用能见度测量值转换得到Vbsca,二者具有较高的相关性(r2=0.84);但存在Vbsca的高值被低估,Vbsca的低值被高估的现象;特别是当Rbsca＞1123 M m-1(对应能见度约小于2.0 km)时,Vbsca的值被低估了17.6％.高浓度PM2.5和高湿度对IMPROVE算法结果有显著的影响.“,”Severe air pollution with visibility deterioration has long been a focus in the North China Plain(NCP).In this study,concentration and light extinction analysis of PM2.5 chemical components were carried out from 2014 to 2017 to study the pollution characteristics in Baoding,a case city of the NCP.The annual average con-centration of total PM2.5 components showed a declining trend,decreasing by 11 μg m-3(water-soluble inor-ganic ions),23 μg m-3(carbonaceous aerosols),and 1796 ng m-3(inorganic elements).Contributing 82.9％to the concentration of total ions,the dominant components,NH4+,NO3-,and SO42-became the main pol-lutants in PM2.5 pollution.Based on the IMPROVE algorithm,the average reconstructed PM2.5 mass concen-tration was 93±69 μg m-3 during the observation period.Meanwhile,the light extinction coefficients were 373.8±233.6 M m-1,405.3±300.1 M m-1,554.3±378.2 M m-1 and 1005.2±750.3 M m-1,in spring,summer,autumn,and winter,respectively.Ammonium sulfate,ammonium nitrate,and organic matter were the largest contributors to light extinction,accounting for a total of 55％-77％in the four seasons.The bsca(light scattering by particles and gases)reconstructed from PM2.5 components(Rbsca)and the bsca converted from visi-bility(Vbsca)were compared to evaluate the performance of the IMPROVE algorithm,revealing a high correlation coefficient of 0.84.The high values of Vbsca were underestimated while the low values were overestimated,as determined through comparison with the one-to-ne line.Especially,when Rbsca＞1123 M m-1(corresponding to＜2.0 km,approximately),Vbsca was underestimated by 17.6％.PM2 5 mass concentration and relative humidity also had an impact on the estimation.