深圳市夏季大气挥发性有机物的光化学反应特征及来源解析

Photochemical reaction characteristics and source apportionment of atmospheric volatile organic compounds during summer in Shenzhen

选取深圳市城市点位在2022年6~8月(夏季)光化学反应活跃季节开展VOCs连续在线观测,利用光化学龄的参数化方法对VOCs测量浓度进行光化学损失校正以获得VOCs初始浓度,并分析VOCs的光化学反应特征,使用特征物种比值分析法和正交矩阵因子模型(PMF)进行VOCs来源解析.研究表明,各类VOCs光化学消耗的浓度在总VOCs(TVOCs)消耗浓度占比为:烯烃(53.5%)、OVOCs(30.8%)、烷烃(10.9%)、芳香烃(4.7%)、乙炔(0.2%).烷烃的初始浓度与测量浓度均在TVOCs中占主导地位,但其光化学损失OFP仅有1.2×10^(-9)远低于烯烃(47.8×10^(-9))、OVOCs(15.8×10^(-9))和芳香烃(4.7×10^(-9)),所以烯烃是臭氧污染防治的关键物种.本研究基于初始值与测量值进行PMF源解析得到6个主要排放源的浓度贡献为(初始-PMF,测量-PMF):工业过程(0.91×10^(-9),0.87×10^(-9))、溶剂使用(2.75×10^(-9),1.84×10^(-9))、汽车尾气(3.49×10^(-9),2.01×10^(-9))、汽油挥发(3.20×10^(-9),2.62×10^(-9))、天然源(0.74×10^(-9),0.56×10^(-9))、燃烧源(2.35×10^(-9),1.16×10^(-9)).结果显示PMF源解析结果受光化学反应影响显著,在进行源解析时应考虑到利用VOCs的初始值而非测量值,否则会对烯烃占主导的汽车尾气与天然源造成显著的低估.

Continuous online VOCs observation was carried out at urban sites in Shenzhen during the active photochemical reaction season from June to August 2022(summer).The photochemical loss VOCs were evaluated based on the measured VOCs concentration using the photochemical age parametric method to obtain the initial VOCs concentration.The sources of initial VOCs were identified by the characteristic species ratio analysis method and Positive matrix factor model(PMF).The concentrations of photochemical consumption VOCs accounted for total VOCs(TVOCs)concentrations as follows:olefin(53.5%),oxygenated volatile organic compounds(OVOCs)(30.8%),alkane(10.9%),aromatic hydrocarbon(4.7%),acetylene(0.2%).Alkanes are dominant compounds in both initial and measured TVOCs concentration,but their photochemical loss ozone generating potential(OFP)is only 1.2×10^(-9),which is much lower than that of olefin(47.8×10^(-9)),OVOCs(15.8×10^(-9))and aromatic hydrocarbons(4.7×10^(-9)),suggesting that olefin is a key species for ozone pollution control.In this study,six major emission sources were obtained by PMF based on measured and initial VOCs concentrations respectively(Initial-PMF,Measured-PMF):industrial processes(0.91×10^(-9),0.87×10^(-9)),solvent use(2.75×10^(-9),1.84×10^(-9)),vehicle exhaust(3.49×10^(-9),2.01×10^(-9)),gasoline volatile(3.2×10^(-9),2.62×10^(-9)),natural source(0.74×10^(-9),0.56×10^(-9)),combustion source(2.35×10^(-9),1.16×10^(-9)).It is suggested that PMF results are significantly affected by photochemical reactions,and the initial value of VOCs rather than the measured value should be considered in source apportionment,otherwise the exhaust gas and natural sources dominated by olefin will be significantly underestimated.