Local and regional contributions to fine particulate matter in Beijing during heavy haze episodes.

In order to alleviate extreme haze pollution, understanding the origin of fine particulate matter (PM2.5 ) is crucial. In this study, we applied Particulate Matter Source Apportionment Technology (PSAT) in CAMx (Comprehensive Air Quality Model with Extensions) to quantify the impacts of emissions from different regions on PM2.5 concentrations in Beijing for haze episodes during January 6-23, 2013. Emission inventory was developed by Tsinghua University. Evolution of local and Regional contributions during local and non-local dominated haze episodes were discussed, separately. In the meanwhile, average contribution of other every city in Jing-Jin-Ji region to PM2.5 concentrations larger than 75μgm-3 in Beijing urban for each range of local contribution percent was analyzed. The results indicate that local emissions contributed 83.6% of PM2.5 at the urban center of Beijing, while regional transport from surrounding cities and parts of Shandong, Henan and Anhui provinces contributed 9.4%; long-range transport contributed the remaining 7.0% mainly from areas >750km away to the south of Beijing during this study period. Compared to non-local-dominated haze episodes, local-dominated heavy haze episodes in Beijing were easily resulted from unfavorable meteorological conditions with much lower PBL and wind velocity. Furthermore, local contribution is more easily to cause a sharp increase or sharp reduction of PM2.5 concentration in central Beijing, reflecting that Beijing local has much stronger potential to form extremely heavy haze episodes. The results indicated that controlling local emissions is a much more important measure to alleviate the extreme haze episodes in Beijing, like that on the night of Jan 12, 2013. Furthermore, emission control in Jing-Jin-Ji region, especially in Tangshan, Tianjin, Baoding, Langfang, Shijiazhuang and Cangzhou, as well as Henan and Shandong province, are important to reduce the PM2.5 concentrations and the occurrence of haze episodes in Beijing.