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 footprint of all heavy air pollution episodes reveals that a wide arc zone in front of the mountains is the most significant source area to air pollution of Beijing. This zone starts approximately from Shijiazhuang in the southwest to Beijing, and then turning to Tangshan in the east.

 Based on the surface data of NCDC (National Climatic Data Center), the wind data of 345 stations during 1985 to 2014 are chosen, the characteristics of low wind-speed meteorology and the distribution of low wind-speed’s mean percentage in China are analyzed. Harbin, Urumqi, Beijing and Chengdu are chosen from 345 stations as representative cities, and the characteristics and annual variabilities of low wind-speed’s percentage are studied. The results show that: 1) The probability of occurrence of low wind-speed is about 40% in China during recent 30 years, as for the four representative cities, Harbin is the lowest (25%), Chengdu is the highest (60%); 2) Time-of-day occurrence: during the period of midnight and early morning, the probability of occurrence of low wind-speed is high; 3) Monthly occurrence: from September or October to next year January, the probability of low wind-speed maintains at a high level, the lowest probability happens in April; 4) Persistence, 36% low wind-speed condition can last at least 3 hours in China, in the four cities, 20% low wind-speed conditon can lasts at leat 12 hours in Chengdu; 5) Distribution, the probability of low wind-speed is high in the South and the inland, while it is low in the North and the coastal; 6) Annual variabilities, Harbin has increasing trend, while other three stations’s long-term trend is not obvious.