基于质子转移飞行时间质谱法对苏州市冬季大气VOCs的观测研究

为分析苏州市城区冬季VOCs污染水平、变化特征及污染来源，采用质子转移飞行时间质谱仪（PTR-TOF-MS）进行走航和定点观测.结果表明:①城区中心走航期间总挥发性有机物（TVOC）平均浓度为95.00 μg/m3，环高架快速路走航期间TVOC平均浓度为131.48 μg/m3，定点观测期间TVOC平均浓度为72.85 μg/m3.对比其他城市城区，苏州市城区VOCs污染较轻，环境空气质量处于优良水平（浓度数据基于PTR-TOF-MS所能观测物种）.②走航及定点观测期间平均浓度最高的均为含氧挥发性有机物（OVOC），城区中心走航区域OVOC占比为35.83%，环高架快速路走航区域OVOC占比为43.33%，定点观测（处于闹市区）期间OVOC占比为33.36%.③观测期间对OFP贡献较大组分为OVOCs、烯烃、芳香烃.结合无机物种定点观测数据发现，VOCs和NO₂的浓度峰值与PM_2.5浓度峰值变化趋势一致.结合VOCs浓度呈早晚高峰的日变化规律，判断机动车尾气可能是VOCs、NO₂、PM_2.5的主要排放源之一.④特征比值法判断观测期间空气老化程度较高，苯系物主要来自交通源和燃料燃烧源.PMF（正矩阵因子分解法）源解析结果表明，VOCs污染源包括溶剂使用源、空气老化和二次形成源、植物源、交通源、工业源，结合非参数风回归模型（NWR）评估污染主要来自定点观测点北方的工业企业以及东南方向的环高架快速行驶的机动车，与走航观测高值点位一致.利用MIR系数法得出5类VOCs来源因子，其OFP贡献率依次为空气老化和二次形成源>溶剂使用源>植物源>交通源>工业源.研究显示，苏州市需加强管控溶剂使用行业的VOCs排放量，倡导在上下班高峰期、周末使用公共交通出行，减少机动车尾气排放，可以有效减少当地O₃生成. 

Observation of VOCs in Suzhou Winter Atmosphere Based on Proton Transfer Time-of-Flight Mass Spectrometry

In order to analyze the pollution level, variation characteristics and pollution sources of VOCs in the urban area of Suzhou in winter, a proton transfer time-of-flight mass spectrometer (PTR-TOF-MS) was used for navigation and fixed-point observation. The results showed: (1) The average concentration of total volatile organic compounds (TVOC) during navigation in the urban center was 95.00 μg/m3, the average TVOC during the ring-elevated expressway navigation period was 131.48 μg/m3, and the average TVOC during the fixed-point observation period was 72.85 μg/m3. Compared with the observed concentrations of VOCs in other urban areas, Suzhou City's VOCs pollution was relatively light, and the ambient air quality was at a good level (the concentration data is based on the species observed by PTR-TOF-MS). (2) During navigation and fixed-point observation, the highest average concentration of TVOC was oxygen-containing volatile organic compounds (OVOC). The OVOC in the central navigation area accounted for 35.83%, and the OVOC in the ring viaduct expressway navigation area accounted for 43.33%. Based on the fixed-point observation in the downtown area, OVOC accounted for 33.36% during the period. (3) During the observation period, the major components that contributed to OFP were OVOC, olefins, and aromatic hydrocarbons. Combined with the fixed-point observation data of inorganic species, it was found that the peak concentration of VOCs and NO₂ was consistent with the peak concentration of PM_2.5. The combined VOCs concentration showed a daily variation of the morning and evening peaks. According to the law, it is judged that motor vehicle exhaust may be one of the main emission sources of VOCs, NO₂ and PM_2.5. (4) The characteristic ratio method determined that the degree of air aging during the observation period was relatively high. The benzene series mainly came from traffic sources and fuel combustion sources. The results of PMF source analysis showed that the sources of VOCs pollution were solvent use sources, air aging and secondary formation, plant sources, and traffic sources. Sources, industrial sources, combined with the non-parametric wind regression model (NWR) assessment determined that the pollution mainly came from industrial enterprises in the north of the fixed-point observation point and fast-moving motor vehicles on the loop elevated in the southeast direction, which is consistent with the high-value point of the navigation observation. The coefficient method derived five types of VOCs source factors, and the OFP contribution rate was in order of air aging and secondary formation sources > solvent use sources > plant sources > traffic sources > industrial sources. The research shows that Suzhou needs to strengthen the control of VOCs emissions from solvent use industries, and advocates the use of public transportation during peak hours and weekends to reduce vehicle exhaust emissions, which can effectively reduce local ozone generation.