上海市光化学污染期间挥发性有机物的组成特征及其对臭氧生成的影响研究

光化学污染导致的高浓度臭氧(O3)是上海面临的重要大气污染问题.本研究分别选取了市区(徐汇)、城郊(青浦)和郊区(南汇)3个典型地区在夏季光化学污染易发季节开展了O3及其前体物挥发性有机物(VOCs)和氮氧化物(NOx)的观测,结合光化学箱模型研究探讨了O3生成的主控污染物.研究表明,不同地区O3污染呈现较强的同步性,日最大浓度也比较接近;但南汇郊区由于受机动车排放影响较小,NOx浓度显著低于其他两个地区,导致该地区O3浓度日变化曲线相对平缓,夜间O3浓度也维持在较高水平.大气VOCs浓度较高时,往往伴随高浓度的O3;3个地区VOCs浓度和组成差异明显,就VOCs浓度而言,徐汇青浦南汇;浓度贡献最主要的物种为甲苯、C2~C3的烷烃和烯烃、丙酮以及辛烷;而C7~C10芳香烃、C3~C4的烯烃、异戊二烯以及乙醛是上海大气臭氧生成潜势贡献最大的VOCs类物质.3个地区O3的生成主要受人为排放的二甲苯类和C3~C4烯烃类物质控制;对于徐汇,只控制NOx会导致O3浓度升高,而南汇郊区O3的生成对NOx排放不敏感.

Characterization of volatile organic compounds (VOCs) and the impact on ozone formation during the photochemical smog episode in Shanghai, China

Shanghai suffered from severe ozone pollution. The characterization of volatile organic compounds (VOCs) and the impact on the ozone (O₃) formation were studied with a focus on the O₃ pollution episode in the summer of 2012 based on the field measurements of O₃ and the precursors at different sites of Shanghai. The O₃ concentrations at different sites showed similar pollution profiles with the similar daily maximum value, whereas O₃ concentrations at night at rural site were significantly higher than those at urban and sub-urban sites due to the less titration of NO. By contrast, there were large differences of VOCs concentrations among different sites as well as the species distribution, and the urban site showed the highest VOCs level followed by those at suburban and rural sites. Generally, the most abundant VOC species in Shanghai were toluene, C2~C3 alkanes and alkenes, octane, and acetone, while the largest contributors of the ozone formation potential (OFP) were C7~C10 aromatics and C3~C4 alkenes. The sensitivity analysis of O₃ formation by using the observation based method (OBM) showed O₃ production was mainly sensitive to the anthropogenic VOCs, especially xylenes and C3~C4 alkenes. As a result, the control of VOCs emissions might be effective in improving the O₃ pollution in Shanghai.While, the control of NO_x might cause the deterioration of O₃ pollution in urban area, it had insignificant effect on the formation of O₃ in rural area.