中文关键词PM_2.5重污染气团轨迹气象要素WRF-CAMx区域传输 英文关键词PM_2.5 heavy pollutionair-mass trajectoriesmeteorological elementsWRF-CAMxregional transport

作者	单位	E-mail
徐冉	国家气象中心, 北京 100081	xuran9011@163.com
张恒德	国家气象中心, 北京 100081	zhanghengde1977@163.com
杨孝文	北京工业大学环境与能源工程学院, 区域大气复合污染防治北京市重点实验室, 北京 100124
程水源	北京工业大学环境与能源工程学院, 区域大气复合污染防治北京市重点实验室, 北京 100124
张天航	国家气象中心, 北京 100081
江琪	国家气象中心, 北京 100081

中文摘要 为了研究近两年北京地区PM_2.5污染特征及成因变化，利用常规观测资料和改进的后向轨迹模型（TrajStat）对2016~2017年秋冬季大气重污染时段的颗粒物浓度、气象要素和气团传输路径进行了综合分析.结果表明，研究期间北京地区共发生13次持续2 d以上的重污染事件，冬季过程约占61.5%，且污染程度和持续时间均高于秋季.地面受弱气压场控制、高湿度、静小风以及较低的混合层高度，加之北京三面环山的特殊地势是导致秋冬季静稳型污染频发的重要因素，重污染期间PM_2.5/PM₁₀的平均比值高达0.86.累积阶段气团主要来自于西北、偏西、西南和东南方向，其中西南和东南路径为典型污染传输通道，轨迹频率为21.6%.此外，采用WRF-CAMx模型定量估算了2016年12月16~22日典型过程中本地和外来污染源对北京PM_2.5的贡献，结果发现不同气团输送条件下，二者的贡献差异较大.当南部气团输入时，本地贡献会显著下降，以外部区域输送为主导；若气流来自西北方向情况则相反.污染过程期间，本地贡献为16.5%~69.3%. 英文摘要 To study the changing of characteristics and formation mechanisms of PM_2.5 in Beijing during the last two years, particulate matter concentrations, weather conditions, and air-mass trajectories were analyzed during severe pollution episodes in fall and winter 2016-2017 using routine observations and the TrajStat model. Results showed that 13 heavy pollution events, each lasting at least two days, occurred in Beijing. Of these, approximately 61.5% occurred in winter, characterized by heavier pollution concentrations and longer durations than those occurring in autumn. A low-pressure gradient, high humidity, low surface wind speed, low boundary layer, and particular terrain (i. e., being surrounded by mountains on three sides) all contributed to the high occurrence frequency of severe pollution episodes in autumn and winter. During the pollution episodes, the average ratio of PM_2.5 to PM₁₀ reached 0.86. The air-masses during the accumulation stage were mainly transported from the northwest, west, southwest, and southeast of Beijing. The southwestern and southeastern transmission paths accounted for 21.6% of the total pollution load. In addition, the WRF-CAMx model was used to quantitatively analyze the contributions of local and external sources to the concentrations of PM_2.5 in Beijing during 16-22 December 2016. Based on this analysis, PM_2.5 contributions notably varied with different air-masses; in the case of southern air-masses, external sources dominated the PM_2.5 concentrations in Beijing and local contributions decreased rapidly; in contrast, in the case of northwestern air-masses, the opposite pattern occurred. Overall, the contribution of local sources to PM_2.5 concentrations in Beijing varied from 16.5% to 69.3% during the monitored pollution episodes.

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