路边微环境PM2.5化学组分特征及来源解析

采集并分析了武汉市机动车尾气源PM_2.5样品，并于2019年10月18~27日采集了武汉市不同路边微环境（市区路边、环线路边、环境背景点）PM_2.5样品并分析其化学组分特征，利用化学质量平衡模型（CMB）解析评估了机动车尾气对城市不同路边微环境PM_2.5的贡献.结果表明，机动车尾气成分谱以OC和EC为主，汽油车OC质量分数约为柴油车的1.14倍，柴油车EC质量分数是汽油车的1.08倍.路边碳组分主要来源于机动车尾气，其中OC浓度在市区路边最高，EC浓度在环线路边最高；市区路边NO₃^-和NH₄⁺浓度较高，与二次转化有关；环线路边Fe、Si、Al质量浓度高于市区路边.CMB来源解析结果显示，机动车尾气源是环线路边、市区路边微环境的主要来源，分担率为35.20%和38.89%，是环境背景点的2倍左右.不同路边微环境污染源贡献差异明显，与环线路边相比，市区路边机动车尾气源与二次来源均相对较高，而扬尘源贡献低于环线路边.

Contributions of vehicle emissions to PM2.5 in roadside microenvironments

To investigate the contribution of vehicle emissions to PM_2.5 in roadside micro-environments in Wuhan, daily PM_2.5 filter samples were collected from different roadside microenvironments (urban roadside, ring roadside) and background site from October 18^th to October 27^th, 2019 in Wuhan. Chemical components of the PM_2.5 samples include elements, carbonaceous materials, and ions were determined. The motor vehicle exhausted PM_2.5 were also collected and analyzed to provide localized source profile for the fitting of chemical mass balance (CMB) model. The results showed that the vehicle exhausted PM_2.5 was dominated by OC and EC. Mass fraction of OC in PM_2.5 from gasoline vehicles was 1.14 times that from diesel vehicles, while the EC from diesel vehicles was 1.08 times that from gasoline vehicles. The fine organic aerosol concentration in roadside was higher than the other sites and largely originated from vehicle exhausts. Concentrations of Fe, Si, and Al at the outer loop line roadside were higher than those at inner-loop urban roadsides. CMB source appointment results showed that the contribution of vehicle emissions to PM_2.5 at the outer loop and inner-loop urban roadsides was 35.20% and 38.89%, respectively, nearly twice that at background site. The sources of PM_2.5 varied with different roadside microenvironments, with vehicle emissions and secondary aerosol had a higher contribution at the inner-loop urban roadside than the outer loop roadside, while dust increased in importance at the outer loop roadside.