运城市夏季O_(3)污染天及清洁天VOCs特征差异及来源解析

Differences of VOCs characteristics and source analysis on O_(3)pollution days and clean days during the summer in Yuncheng

利用2021年6月1日—8月31日运城市水厂站点提供的主要大气污染物数据(O_(3)、PM_(2.5)、PM_(10)、NO、NO_(2)、CO、SO_(2))、气象参数及TVOCs和VOCs各物种浓度值,对运城市夏季空气质量整体情况进行了分析,并重点分析了O_(3)污染天和清洁天VOCs的特征及来源差异.结果表明,运城市夏季O_(3)、TVOCs和NO_(x)的月均浓度最高值出现在6月,且其污染天的日浓度变化规律与清洁天一致,但污染天的日变化峰谷值差距明显更大,O_(3)与NO_(x)、TVOCs、CO和相对湿度呈负相关,与温度呈正相关,其浓度高低主要受前体物及气象要素的影响;夏季各种类VOCs混合比为OVOCs>烷烃>卤代烃>烯烃>乙炔>芳香烃,日变化峰谷值差距为烷烃>OVOCs>烯烃>乙炔>芳香烃>卤代烃,在二次转化过程中贡献较高的种类为烷烃、OVOCs和烯烃;运城市夏季整体污染源呈现机动车排放源>工业源>二次转化源>LPG/NG使用源>燃烧源>自然源的特征,机动车源对VOCs的贡献显著,且机动车源对污染天的影响小于清洁天,污染天工业源对VOCs的贡献大于清洁天;OVOCs对二次转化过程贡献占比最大(57.19%~65.00%),其次为烯烃(15.39%~29.59%),污染天OVOCs和芳香烃的贡献均大于清洁天;运城市夏季主要处于VOCs和NO_(x)协同控制区及NO_(x)控制区.

Based on the major air pollutant data(O_(3),PM_(2.5),PM_(10),NO,NO_(2),CO,SO_(2),VOCs)and meteorological parameters provided by Yuncheng water plant station from June 1 to August 31,2021,a comprehensive analysis of summer air quality in Yuncheng was conducted..A detailed investigation was carried out to explore the characteristics and source disparities of VOCs between O_(3)pollution days and clean days.The results revealed that the highest monthly average concentrations of O_(3),TVOCs and NO_(x)in Yuncheng in the summer were observed in June,and the daily concentration variations of the pollution days was consistent with those on clean days,while there were more significant differences between the daily peak and valley concentration values on pollution days.O_(3)was negatively correlated with NO_(x),TVOCs,CO and relative humidity,whereas it positively correlated with temperature.O_(3)concentration was primarily affected by precursors’concentrations and meteorological conditions.In the summer,the mixing ratios of VOCs followed the order of OVOCs>alkanes>halogenated hydrocarbons>alkenes>alkynes>aromatics,and the difference between the daily peak and valley values ranked as alkanes>OVOCs>alkenes>alkynes>aromatics>halogenated hydrocarbons.Alkanes,OVOCs and alkenes exhibited higher contributions to secondary transformation compared to other VOCs groups.The VOC source contributions of Yuncheng in the summer presented the characteristics:vehicle emissions>industrial sources>secondary transformation>LPG/NG usage>combustion sources>biogenic sources.The vehicle contribution to VOC concentrations was significant,and the proportion of vehicle sources on pollution days was less than that on clean days.Similarly,the contribution of industrial VOCs on pollution days was less than that on clean days;The contribution of OVOCs to the secondary transformation was the largest(57.19%~65.00%),followed by alkenes(15.39%~29.59%),and the contributions of OVOCs and aromatics on pollution days were greater than that on clean days.The O_(3)formation regimes in Yuncheng were dominant by transition regime and NO_(x)-limited regime in the summer.