Ozone source attribution during a severe photochemical smog episode in Beijing, China

Beijing, the capital of China, frequently suffers from the high levels of ozone in summer. A 3-D regional chemical transport model, the Comprehensive Air Quality Model with extensions (CAMx), has been used to simulate a heavy O-3 pollution episode in Beijing during June 26-July 2, 2000. Ozone Source Apportionment Technology (OSAT) and Geographic Ozone Assessment Technology (GOAT) were applied to quantify the contributions of the precursor emissions from different regions to O-3 concentrations in Beijing, to identify the relative importance of different ways by which regional sources affected the O-3 levels in Beijing urban areas, and to investigate the sensitivity of O-3 formation to the precursors during the episode. The O-3 pollution in Beijing showed a significant spatial distribution with strong regional contribution. The results suggested that the plume originating from Beijing urban areas greatly affected the O-3 concentrations at the Dingling site, accounting for 55% of elevated O-3 there, while O-3 pollution in the Beijing urban areas resulted from both local emissions and those from Tianjin and the south of Hebei Province. Transport of O-3 was responsible for about 70% of the regional O-3 contribution to Beijing urban areas, while transport of O-3 precursors accounted for the remainder. The formation of O-3 was limited by volatile organic compounds (VOCs) in the urban areas of Beijing, while being more sensitive to NO (x) levels in the suburban and more remote areas. Therefore, it is necessary to consider a large number of factors, including impacts of emissions from different regions, the two modes of regional contribution as well as the sensitivity of O-3 formation to precursors, in the design of emissions control strategies for O-3 reduction in Beijing.