北京地区臭氧污染的来源分析

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

光化学烟雾污染是影响北京地区夏季空气质量的一个重要环境问题.利用区域空气质量模式(CAMx)对2000年6月底至7月初发生在北京地区的臭氧污染过程进行模拟,运用臭氧源识别技术(OSAT)和地区臭氧评估技术(GOAT),量化了不同地区的污染源排放对北京市城近郊区臭氧污染的贡献,探讨了周边地区排放的臭氧贡献方式问题,分析了北京地区臭氧污染的化学机制特征.研究表明,北京地区臭氧污染分布存在显著差异,并且具有明显的区域性特征,定陵地区的超标臭氧主要受到城近郊区烟羽的严重影响(占55%),城近郊区则除了受到北京市的前体物排放影响外(占46%),来自天津市、河北省南部地区的贡献往往也占有重要份额;周边地区对北京市城近郊区的贡献中,直接输入的臭氧约占七层,其余部分以输入前体物的方式贡献臭氧;北京城近郊区的臭氧生成主要受挥发性有机物控制,而在远郊区县和农村地区臭氧生成对氮氧化物变得更为敏感.对北京地区臭氧污染的源排放控制,需要综合考虑各种臭氧来源和不同贡献方式的重要性,以及臭氧生成机制的变化规律.

Beijing, the capital of China, frequently suffers from 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 O3 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 precursor emissions from different regions to O3 concentrations in Beijing, to identify the relative importance of different ways by which regional sources affected the O3 levels in Beijing urban areas, and to investigate the sensitivity of O3 formation to precursors during the episode. The O3 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 O3 concentrations at the Dingling site, accounting for 55% of elevated O3 there, while O3 pollution in the Beijing urban areas resulted from both local emissions and those from Tianjin and the south of Hebei Province. Transport of O3 was responsible for about 70% of the regional O3 contribution to Beijing urban areas, while transport of O3 precursors accounted for the remainder. The formation of O3 was limited by volatile organic compounds （VOCs） in the urban areas of Beijing, while being more sensitive to NOx 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 O3 formation to precursors, in the design of emissions control strategies for O3 reduction in Beijing.