• 关键词：PM_2.5  时空分异特征  气象条件  后向轨迹

• 基金项目：国家自然科学基金（No.41471076）；上海市2017年度"科技创新行动计划"长三角科技联合攻关项目（No.17295810603）；上海市自然科学基金（No.17ZR1408700）；上海市城市化生态过程与生态恢复重点实验室开放课题（No.SHUES2016B04）

• 佘倩楠
• 1. 华东师范大学生态与环境科学学院, 上海 200241;2. 上海市城市化生态过程与生态恢复重点实验室, 上海 200241

• 徐茜
• 华东师范大学生态与环境科学学院, 上海 200241

• 周陶冶
• 上海市浦东新区环境监测站, 上海 200135

• 冯通
• 华东师范大学地理科学学院, 上海 200241

• 任浙豪
• 华东师范大学地理科学学院, 上海 200241

• 刘敏
• 1. 华东师范大学生态与环境科学学院, 上海 200241;2. 上海市城市化生态过程与生态恢复重点实验室, 上海 200241;3. 崇明生态研究院, 上海 200062

• 摘要：基于2015年长三角地区129个环境空气质量监测站的空气质量指数（AQI）及主要大气污染物浓度数据，结合气象资料和HYSPLIT后向轨迹模式，探究长三角地区大气重污染的时间变化和空间集聚特征，并深入分析气象条件和区域传输对重污染过程发生和维持的影响.结果表明，2015年长三角地区各城市平均出现AQI超过200的重污染天气共8 d，重污染频率为2.01%，PM_2.5作为首要污染物出现频次最多.从时间变化看，重污染主要分布在1月和12月；从空间分布看，北部地区重污染相比南部地区更为严重，徐州和常州市出现频率最高.选取典型重污染过程1月9—11日（纬向扩散型）、1月24—26日（经向扩散型）和12月20—26日（两种模式相结合的重污染天气）进行成因分析，发现长三角地区重污染天气主要受到西北风向、低风速、高湿度和逆温层的影响，导致大气污染物积累且不易扩散.基于HYSPLIT的大气传输轨迹及频率分布表明，来自西北方向的气流对江苏北部地区的污染输送特征有着显著影响.

• Abstract：We analyzed ground air quality measurements from 129 monitoring stations in the Yangtze River Delta (YRD) region during 2015 to examine the spatial and temporal variabilities of severe air pollution episodes in this region. By using the meteorological information and backward trajectory model, we investigated the effects of meteorological factors and regional transport on typical severe air pollution episodes. There were on average eight days of severe air pollution (AQI >200) in 2015 in each city, and PM_2.5 was the primary contributor. High AQI days were mainly concentrated in January and December. Spatially, monitoring data indicated more frequent high pollution days in the northern region of the YRD as compared to the southern region. In particular, Xuzhou city and Changzhou city had seen the most frequent high pollution days. We then analyzed three representative large regional episodes, i.e., a "north-south diffusion type" during January 9-11, an "east-west diffusion type" during January 24-26, and a "multi-process diffusion type" during December 20-26. During these heavy air pollution episodes, the predominant wind was of northwesterly direction, and the atmosphere was more stagnant as indicated by lower wind speeds and high relative humidity. Analysis of the backward trajectories and frequency distributions showed that the airflow from the northwest had an important influence on the transport of air pollutants in the YRD and particularly the northern region of Jiangsu Province.

• Key words：PM_2.5  spatial and temporal variability  meteorological condition  backward trajectory model

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