北京市春季交通干道移动源非甲烷总烃的在线跟踪观测与特征分析

Mobile online-monitoring and characteristic analysis of non-methane hydrocarbon on main traffic road in Beijing in spring

机动车排放(Vehicular Emission,VE)是地面非甲烷烃(Non-methane hydrocarbon,NMHCs)的重要人为源之一.为获得北京市交通主干道NMHCs的实际排放情况,本研究以自主研发的吸附/热解吸前处理-单光子/化学复合软电离源飞行时间质谱(SPI/CI-TOFMS)为检测手段,于2018年3月14日在北京四环、五环主干道,对C2~C10挥发性有机物进行了车载在线跟踪观测.结果表明,C2、C3高挥发性物质浓度较高,其次是苯系物和丁烷;从空间分布来看,NMHCs浓度在离市中心较近的四环主干道相对较高,且车流量较大的南五环公路和西四环处NMHCs污染也较为严重;从NMHCs的结构组成来看,烷烃(63%、52%)占比最多,芳香烃(23%、32%)次之,烯烃(14%、16%)最少;对NMHCs特征物质之间的线性关系和比值关系进行分析,确定机动车排放对此次观测中NMHCs的生成贡献较大;通过计算各物种臭氧生成潜势(OFP),评估出C3、C4烯烃类物质和苯系物为北京四、五环地区优先控制物种.

Vehicular emission(VE) is one of the most significant anthropogenic sources of ambient non-methane hydrocarbons(NMHCs) in urban areas, especially in megacities like Beijing. To better understand the distribution, composition, and emissions of NMHCs on Beijing ring roads, a self-developed instrument is deployed on-board for real-time measurement of NMHCs on fourth and fifth ring road. The instrument is based on absorption/thermal desorption method for pre-concentration, and a single photon/chemical complex soft ionization time-of-flight mass spectrometry(SPI/CI-TOFMS) is used for detection. Results show that the highly volatile C2, C3 NMHCs are the major species, followed by aromatics and butane. NMHCs levels are generally more elevated on fourth ring than fifth ring, due to severer traffic. For similar reasons, pollution is more serious at the south fifth ring and the west fourth ring. Alkanes were found to be most abundant(63%,52%), aromatics(23%,32%) and alkenes(14%,16%) follow. Based on analysis on benzene/toluene ratio and benzene/acetylene ratio, we conclude that vehicle exhaust is the dominant source during the observation periods for aromatics, while other sources may also contribute to the observed acetylene level. Through evaluation of the ozone formation potential(OFP) for each species, we recommend C3, C4 alkenes and the aromatics to be the prioritized pollutants for control strategies.