成都市城区大气VOCs季节污染特征及来源解析

为研究成都市城区大气VOCs季节变化特征,本研究在2018年12月至2019年11月对VOCs组分进行监测,并对VOCs的浓度水平、各化学组成、化学反应活性和来源进行分析.结果表明,成都市城区春、夏、秋和冬季VOCs的平均体积分数分别为32.29×10~(-9)、 36.25×10~(-9)、 40.92×10~(-9)和49.48×10~(-9),冬季的浓度明显高于其他季节,春季和夏季的浓度水平相差不大,各季节VOCs的组分浓度水平有所差异,冬季烷烃占总VOCs的比例最大,可能受机动车排放的影响较明显;夏季和秋季含氧(氮)挥发性有机物占比远高于春、冬季,一次源的挥发排放和二次转化的生成贡献较大;成都市城区不同季节大气中VOCs平均浓度排名靠前的关键组分基本无变化,主要是C_2～C_4的烷烃、乙烯、乙炔及二氯甲烷等,可能受机动车尾气、油气挥发、溶剂使用和LPG燃料等影响明显,夏季丙酮以及乙酸乙酯等含氧有机物浓度贡献突出;根据·OH消耗速率和OFP计算可知关键活性物种主要为间/对-二甲苯、乙烯、丙烯、1-己烯、甲苯、异戊烷和正丁烷等,这些物种应该优先减排和控制;四季VOCs源解析结果显示:春、夏季温度较秋、冬季高,光照更强,PMF明显解析出天然源和二次排放贡献,同时,由于夏季温度较高,解析出油气挥发占9%;秋、冬季占比增加的源主要为机动车尾气和燃烧源,燃烧源的排放占比在25%左右,另餐饮源的排放占比在9%左右.

Seasonal Pollution Characteristics and Analysis of the Sources of Atmospheric VOCs in Chengdu Urban Area

To investigate the seasonal variations in the concentrations of atmospheric volatile organic compounds (VOCs) in the urban area of Chengdu, VOC species were monitored from December 2018 to November 2019, and the concentrations, chemical composition, chemical reactivity, and sources of VOCs were analyzed. Average volume fraction of VOCs in spring, summer, autumn, and winter are 32.29×10^-9, 36.25×10^-9, 40.92×10^-9, and 49.48×10^-9, respectively. The concentrations in winter are significantly higher than the winter concentrations measured in other areas. There is no significant difference between VOC concentrations in spring and summer, but component concentrations vary from season to season. In winter, alkanes account for the largest proportion of total VOCs owing to vehicle emissions. The proportion of oxygen (nitrogen)-containing volatile organic compounds in summer and autumn is much higher than that in spring and winter. Volatile emissions from primary sources and secondary conversions have a great contribution. The average concentration of key components of VOCs in different seasons did not change significantly. C₂-C₄ alkanes, ethylene, acetylene, and dichloromethane concentrations may be significantly affected by vehicle exhaust, oil and gas volatilization, solvent use, and LPG fuel use. ·OH consumption rate and OFP calculations show that key active species are mainly m/p-xylene, ethylene, propylene, 1-hexene, toluene, isopentane, and n-butane. Therefore, these species should be given priority in emissions control measures. Since the temperature in spring and summer is higher than in autumn and winter, and the UV rays are more intense, PMF analysis reveals the natural sources and the secondary emission sources as the major sources. The oil and gas volatilization source contributes to 9% of VOC concentrations in summer. The major VOC sources in autumn and winter are vehicle exhaust and combustion sources. Emissions from the combustion sources contribute to 25% and emissions from the catering sources in autumn and winter contribute to 9% of total VOC levels.