成都夏冬季PM2.5中水溶性无机离子污染特征

Pollution Characteristics of Water-soluble Inorganic Ions in Chengdu in Summer and Winter

利用大气细颗粒物水溶性组分及气态前体物在线监测设备(GAC-IC)对成都市2017年夏、冬两季大气PM2.5中水溶性无机离子(WSIIs)及气态前体物进行了连续观测,对其污染特征及冬季一次典型污染过程进行了深入分析.结果表明,成都冬季PM2.5质量浓度为100.2μg·m-3,显著高于夏季(34.0μg·m-3).WSIIs是PM2.5的重要组成,对夏、冬季PM2.5的贡献分别可达52.9%和53.3%.夏、冬季的二次离子(SNA)占WSIIs的比例分别为73.2%和87.6%,其中,SO42-和NO-3分别是夏、冬季SNA的主导组分,对SNA的贡献分别为37.7%和59.7%.冬季NO-3/SO42-比值(2.7)显著高于夏季(0.8),体现了移动源(尤其是机动车源)对该季节PM2.5的重要贡献.受来源及气象条件差异的影响,两季节SNA的日变化规律明显.在冬季,随着污染加重,各化学组分及主要气态前体物浓度均显著增加,NO-3是引发重污染的关键组分.后向轨迹分析表明,成都两季节气团来向差异明显,夏、冬季聚类对应的WSIIs分别以SO42-和NO-3为主导,成都周边地区的近距离低空传输对该城市PM2.5污染贡献重大.

The water-soluble inorganic ions(WSIIs)in PM2.5 and gaseous precursors of Chengdu were continuously observed by a gas and aerosol collector combined with ion chromatography(GAC-IC)in the summer and winter of 2017,and both their pollution characteristics and a typical pollution process in winter were analyzed.It was found that the concentration of PM2.5 in winter(100.2μg·m-3)was significantly higher than that in summer(34.0μg·m-3).WSIIs were important components of PM2.5 and their total contributions to PM2.5 were 52.9%and 53.3%in summer and winter,respectively.Secondary ions(SNA)accounted for 73.2%and 87.6%of WSIIs in summer and winter,respectively.SO42-and NO3-dominated the SNA in summer and winter,and the contributions to SNA were 37.7%and 59.7%,respectively.The NO3-/SO42-ratio(2.7)in winter was significantly higher than that in summer(0.8),reflecting the important contribution of mobile sources(especially motor vehicles)to PM2.5 in this season.The diurnal variation of SNA in the two seasons was obviously different due to the differences in sources and meteorological conditions.In winter,with the aggravation of pollution,the concentrations of WSIIs and gaseous precursors increased significantly,and NO3-was the key component in causing heavy pollution.Backward trajectory analysis revealed that the air masses in the two seasons in Chengdu differed significantly from each other.The WSIIs in summer and winter were dominated by SO42-and NO3-,respectively.The short-distance and low-altitude transmission from the east and south of Chengdu contributed significantly to PM2.5 pollution in Chengdu.