郑州市一次连续臭氧污染过程的特征及源解析

Characteristics and Source Apportionment of a Persisting Ozone Pollution Episode in Zhengzhou City

为探究夏季臭氧(O_(3))连续污染时段挥发性有机化合物(VOCs)污染特征及来源贡献,对郑州市大气环境中VOCs进行监测,分析了O_(3)污染形势及其前体物与气象的关系,探究O_(3)和VOCs的污染特征,并对比分析了关键活性组分,重点利用比值法和正定矩阵因子分析(PMF)受体模型研究了其来源贡献。结果表明:①郑州市6月O_(3)污染具有浓度高、连续时间长及污染天数多等特点,在强辐射、高温、低湿和风速较小等不利气象条件下,高浓度VOCs与NO_(2)发生光化学反应,造成O_(3)持续生成及累积,导致O_(3)连续超标且高值频发。②郑州市VOCs浓度为(74.7±29.1)μg/m^(3),组分中以烷烃、卤代烃和含氧挥发性有机物(OVOCs)为主。臭氧生成潜势(OFP)和羟基消耗速率(LOH)分析显示,VOCs中关键活性组分呈烯烃>OVOCs>烷烃>芳香烃的特征,活性物种为异戊二烯、乙烯、丙醛、丙烯、2-己酮、1-己烯和异戊烷等。③郑州市VOCs光化学初始浓度为82.5μg/m^(3),较观测值高7.8μg/m^(3),且下午比上午VOCs的光化学反应消耗明显。④机动车尾气排放源、溶剂涂料使用源和油气挥发源是此次污染过程中VOCs排放的主要来源,贡献率分别为27.0%、26.6%和26.0%,其中溶剂涂料使用源和机动车尾气排放源是对O_(3)生成贡献最大的来源,贡献率分别为27.3%和22.2%。研究显示,郑州市6月O_(3)连续污染主要由于在不利气象条件下,促使较高浓度VOCs和NO_(2)发生光化学反应,造成O_(3)连续超标且高值频发,因此亟需重点加强VOCs中关键活性组分的污染源减排,尤其强化机动车尾气排放源和溶剂涂料使用源的管控力度,从而缓解O_(3)污染。

In order to explore the characteristics and source contributions of volatile organic compounds(VOCs)pollution during the summer,a persistent ozone(O_(3))pollution episode in Zhengzhou City was selected for investigation.The relationship between O_(3) pollution,its precursors,and meteorological conditions was analyzed,and the pollution characteristics of O_(3) and VOCs were compared and explored.Various VOC activity evaluation methods,including ozone formation potential(OFP)and OH consumption rate(LOH),were used to解决方案研究项目(No.2022-10)identify key active components and species.Additionally,ratio analysis method and positive matrix factorization analysis(PMF)model were employed to study the contribution of VOC sources.The results showed that:(1)The episode was characterized by persistent high O_(3) concentrations and pollution days in June in Zhengzhou City,primarily due to severe meteorological conditions such as strong radiation,high temperature,low humidity,low wind speed,and the photochemical reaction of high concentrations of VOCs and NO_(2).(2)The VOC concentration in Zhengzhou City was(74.7±29.1)μg/m^(3),with the main components being alkanes,halogenated hydrocarbons,and oxygenated volatile organic compounds(OVOCs).OFP and LOH analysis showed that the key active components of VOCs were ordered as olefin>OVOCs>alkanes>aromatics.OFP and LOH were roughly the top 10 active species,including isoprene,ethylene,propionaldehyde,propylene,2-hexanone,1-hexene and isopentane.(3)The calculated photochemical VOC concentration in Zhengzhou was 82.5μg/m^(3),3 about 7.8μg/m higher than the observed value,with significant VOC consumption due to photochemical reactions in the afternoon compared to the morning.(4)Ratio analysis and PMF source apportionment indicated that vehicle exhaust emissions,solvent coating sources,and oil and gas volatile sources were the primary sources of VOC pollution,with contribution ratios of 27.0%,26.6%and 26.0%,respectively.Among these,solvent coating usage and vehicle exhaust emissions were the major contributions to O_(3) formation,with contributions of 27.3%and 22.2%,respectively.Research shows that the persistent June O_(3) pollution episodes in Zhengzhou City are primarily due to the high concentrations of VOCs and NO_(2) under severe meteorological conditions,which promotes photochemical reactions,resulting in ozone exceeding standard limit and frequent high values.Therefore,it is urgent to strengthen the emission reduction of key active components in VOCs and especailly to tighten the emission controls of vehicle exhausts and solvent coating sources to mitigate O_(3)pollution in Zhengzhou.