常州一次重污染过程气象条件及PM_(2.5)组分特征分析

Analysis of Meteorological Conditions and PM_(2.5)Components Characteristics of One Severe Air Pollution Event in Changzhou,Jiangsu Province

利用气象数据、PM_(2.5)质量浓度、化学组分等多种实测资料,分析了2018年1月1423日常州持续重污染过程演变特征,探讨了不同污染阶段南京、常州、苏州PM_(2.5)质量浓度的变化差异。结果表明:常州此次污染机动车、燃煤和生物质燃烧影响大,大致可分为静稳初期污染累积、周边污染扩散叠加、强冷空气污染输送三个阶段。第一阶段在高温、高湿和低风速等不利气象条件下,常州PM_(2.5)质量浓度逐渐升高,Cl^(-)浓度占比增加,本地污染特征明显,移动源的贡献远大于固定源的贡献。第二阶段污染形势最为严峻,常州重污染持续时间长达56 h,PM_(2.5)峰值浓度最高达到261μg·m^(-3),NO^(-)_(3)、NH^(+)_(4)、Na^(+)、K^(+)、Ca^(2+)浓度占比增加,SOR和NOR分别达到0.55和0.41,二次转化特征明显。第三阶段为强冷空气南下带来的暴发式重污染,PM_(2.5)质量浓度约以每小时30μg·m^(-)_(3)速度呈现骤升骤降的变化特征,Cl^(-)、Na^(+)、Mg^(2+)和Ca^(2+)浓度占比降低,SNA占比最大,SO_(2)和NO_(2)等前体物二次转化效率最高,SO^(2-)_(4)对PM_(2.5)质量浓度贡献更加明显。通过对比南京、常州与苏州PM_(2.5)质量浓度变化特征发现,静稳天气阶段,三座城市PM_(2.5)质量浓度变化趋势较为一致;污染时段风速对PM_(2.5)质量浓度影响较大,常州风速最低、PM_(2.5)质量浓度最高,苏州相反。

The meteorological data and PM_(2.5) mass concentration data,chemical compositions and other observations are used to analyze the evolution characteristics of continuous severe haze in Changzhou from January 14 to 23,2018.The differences in PM_(2.5) concentration at different pollution stages in Nanjing,Changhzou and Suzhou are discussed.The results show that the motor vehicles,coal and biomass combustion had a great impact on this pollution process which can be roughly divided into three stages:pollution accumulation,peripheral pollution diffusion,and strong cold air pollution transport.In the first stage,high temperature,high humidity,and low wind speed promoted the increase of PM_(2.5) concentration in Changzhou.Local pollution characteristics were obvious as the proportion of Cl^(-) concentration increased significantly and the contribution of mobile sources was much greater than that of stationary sources.The pollution situation in the second stage was most serious and kept at a high level for 56 hours with the highest PM_(2.5)concentration reaching 261μg·m^(-3)and the proportions of NO^(-)_(3),NH^(+)_(4),Na^(+),K^(+)and Ca^(2+)increased as well.SOR and NOR reached 0.55 and 0.41 respectively,which indicates the characteristics of secondary transformation were obvious.The third stage was characterized by sudden increase and decrease of PM_(2.5)concentration at the speed of 30μg·m^(-)_(3)per hour,caused by the strong cold air.The concentrations of Cl^(-),Na^(+),Mg^(2+)and Ca^(2+)were the lowest,but the proportion of SNA was the highest.The long-distance transport process strengthened the secondary conversion of SO_(2)and NO_(2)precursors,and SO^(2-)_(4)had more obvious impact on PM_(2.5)concentration.By comparing the characteristics of PM_(2.5)concentrations in Nanjing,Changzhou and Suzhou,we found that the variation trend of PM_(2.5)mass concentration in the three cities was relatively consistent in the calm weather stage.The wind speed had a great influence on the mass concentration of PM_(2.5)during the pollution period.Changzhou had the lowest wind speed and the highest PM_(2.5)concentration,while Suzhou was opposite in the stagnant meteorological condition.