Long-term Mean Footprint and Its Relationship to Heavy Air Pollution Episodes in Beijing

ZOU Qingqing1, CAI Xuhui1,†, GUO Mengting1, SONG Yu1, ZHANG Xiaoling2

1. State Joint Key Lab of Environmental Simulation and Pollution Control, Department of Environmental Sciences, College of Environmental Sciences and Engineering, Peking University, Beijing 100871; 2. Environmental Meteorology Forecast Center of Beijing-tianjin-hebei, Beijing 100089; † Corresponding author, E-mail: xhcai@pku.edu.cn

Abstract Potential source area (footprint) related to air pollution of Beijing is investigated. Long-term modeling of meteorological fields is carried out by WRF model, from 2000 to 2014. A backward dispersion footprint model is used to derive hourly footprint using these meteorological data. Long-term mean source area is obtained as well as its seasonal variation. Heavy air pollution episodes in winter and autumn are selected from air pollution index (API) data in the period from 2000 to 2012. Relationship between air pollution and its potential source area is discussed. Results show that daily mean footprint varies both by its pattern and direction, indicating strong temporal variation of the source areas for Beijing. Long-term mean source area for Beijing is shaped like a triangle, and the southwest branch is the strongest, the other two are in the east and north. Beijing locates in the middle to norther position of the triangle. Seasonal variation of the mean source area show enhancement in the southwest and south in summer (July) and autumn (October). Local wind frequency may mislead assessment of source area, in comparison to the footprint derived by the backward dispersion model. By handling all dispersion processes, such as accumulation of air borne materials, the footprint model provides reasonable information of source area. Mean

北京科学技术委员会首都蓝天行动培育专项(Z141100001014013)、国家科技支撑计划(2014BAC06B02)、国家自然科学基金(41421064, 41575007, 91544216)和环境保护公益性行业科研专项(201509001, 201409001)资助收稿日期: 20161231; 修回日期: 20170315; 网络出版日期: 20170728

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