我国中东部地区城乡(郊)地面O_(3)和VOCs的联合在线观测研究

Observation and Comparative Study of Ground-Level O_(3)and VOCs in Urban and Rural(Suburban)Areas in Central-Eastern China

针对快速工业化和城镇化带来的新形势下的环境问题,2021年6−9月国家大气污染防治攻关联合中心同步开展了4组(北京市、保定市、廊坊市和上海市)城乡(郊)臭氧(O_(3))和大气挥发性有机物(VOCs)的在线观测与比对研究.结果表明:①在我国O_(3)污染较严重的中东部地区,以往“郊乡地区O_(3)浓度明显高于城区”的O_(3)污染特征正在改变,3个北方城市(北京市、保定市和廊坊市)的城区O_(3)浓度不同程度地高于其邻近的郊乡地区,上海市则呈现城郊趋同的态势.②这4组城乡(郊)之间VOCs浓度差异较小,VOCs组成中均为烷烃占比最高,在3个北方城市(北京市、保定市和廊坊市)其占比在70%左右,而上海市则在60%左右.③对O_(3)生成潜势(OFP)贡献较大的VOCs类别主要为芳香烃和烯烃,对OFP贡献较大的VOCs物种主要为乙烯、间/对-二甲苯、甲苯和异戊二烯等.④O_(3)生成敏感性分析(EKMA曲线)表明,北京市城郊、保定市城乡和上海市城区为VOCs控制区,其他城乡(郊)则呈现VOCs和氮氧化物(NOx)协同控制的特征.我国中东部85个城市中,卫星反演获得的甲醛与二氧化氮柱浓度比值在2018−2021年呈下降趋势,说明我国中东部郊乡地区O_(3)生成敏感性向VOCs控制区转变的现象普遍存在.研究显示,我国中东部地区“O_(3)城乡差异”较以往已发生深刻变化,无论在O_(3)的浓度水平、生成敏感性及其前体物来源和空间分布等方面都呈现出“趋同”之势.

In order to address the new environmental problems brought by rapid industrialization and urbanization,online observations and comparative studies of ozone(O_(3))and volatile organic compounds(VOCs)were simultaneously carried out by the National Joint Center for Air Pollution Prevention and Control in four cities(Beijing,Baoding,Langfang and Shanghai)in Central-Eastern China from June to September in 2021.The results are as follows:(1)It was found that the characteristic of O_(3)pollution that used to be‘significantly higher in rural and suburban areas than in urban areas’has been changing in Central-Eastern China where O_(3)pollution was seriously worsened.The ozone concentrations were all higher in urban areas of the three northern cities(Beijing,Baoding and Langfang)than those in their adjacent rural(suburbs)areas in different degrees.A similar serious O_(3)pollution level was observed in both urban and suburban areas of Shanghai.(2)There was little difference in VOCs concentrations between the four pairs of urban and rural(suburbs)areas.The most important components of VOCs were alkanes,accounting for about 70%in the three northern cities and about 60%in Shanghai.(3)Aromatics and olefins were the major contributors to the ozone formation potential(OFP),particularly ethylene,m-xylene,toluene and isoprene.(4)The O_(3)formation sensitivity analysis(EKMA curve)indicated that the VOCs-limited regimes were mainly controlled in Beijing(both in the urban and suburban areas),Baoding(both in the urban and rural areas)and Shanghai(only in the urban area),while the other areas in this study belonged to a VOCs-NOx transitional control regime.The formaldehyde to NO2 concentration ratios(FNR)in 85 cities in Central-Eastern China showed a decreasing trend between 2018 and 2021,which indicated that the transition of O_(3)formation sensitivity to a VOCs-limited regime was widespread.In summary,there is a profound change of the‘O_(3)urban-rural difference’compared to the past.This indicates that there is a trend of convergence in terms of O_(3)concentration level,formation sensitivity,and emission sources and spatial distribution of O_(3)precursors in Central-Eastern China.