Kong Lan, Zhou Li, Chen Dongyang, Luo Lan, Xiao Kuang, Chen Yong, Liu Hefan, Tan Qinwen, Yang Fumo
College of Carbon Neutrality Future Technology, Sichuan University, Chengdu 610065, China; College of Architecture and Environment, Sichuan University, Chengdu 610065, China; Yibin Institute of Industrial Technology, Sichuan University Yibin Park, Yibin 644000, China.
College of Carbon Neutrality Future Technology, Sichuan University, Chengdu 610065, China; College of Architecture and Environment, Sichuan University, Chengdu 610065, China; Yibin Institute of Industrial Technology, Sichuan University Yibin Park, Yibin 644000, China.
Sci Total Environ. 2023 Nov 25;901:166259. doi: 10.1016/j.scitotenv.2023.166259. Epub 2023 Aug 17.
Volatile organic compounds (VOCs) are significant precursors to photochemical pollution. However, reactive VOC species are easily oxidized during transportation, resulting in a systematic underestimate of the measured concentrations. To address this, we applied an improved calculation method to correct the measured VOC concentrations into photochemical initial concentrations (PICs) in Chengdu, a megacity in the Sichuan Basin, China, which is highly vulnerable to complex pollution. In this study, 56 VOC species on the Photochemical Assessment Monitor Station (PAMS) target list were quantitatively monitored throughout all four seasons. Comparing to directly measured values, photochemically initialized total mixing ratios of VOCs increased by 18.6 % in general. The photochemical loss percentages of alkenes and aromatics were prominent in summer (68.6 %, 28.7 %) and spring (65.9 %, 24.7 %), respectively. Furthermore, we examined contributions of VOCs to atmospheric oxidation capacity (AOC) depending on PICs and found that maximum daily total AOC showed a surge in spring and summer. Besides hydroxyl radicals, daytime O in spring and late-afternoon nitrate radicals in summer were essential for AOC with PICs. As expected, alkenes and aromatics dominated PIC-based ozone formation potentials (OFPs). Furthermore, contribution of alkenes to secondary organic aerosol formation potentials reached 15.5 % and 7.6 % in spring and summer, respectively. Using positive matrix factorization model, we identified five VOC sources including vehicular exhaust, industrial emissions, solvent usage, biogenic sources, and liquefied petroleum gas/natural gas use. Based on PICs, biogenic sources were significantly underestimated in spring and summer. Meanwhile, m,p-xylene from solvent usage and isoprene from biogenic sources were the primary contributors to OFPs. Consequently, these results emphasize the significance of photochemically oxidized VOC concentrations, especially for reactive species in typical seasons.
挥发性有机化合物（VOCs）是光化学污染的重要前体物。然而，活性VOC物种在传输过程中容易被氧化，导致实测浓度被系统性低估。为解决这一问题，我们应用一种改进的计算方法，将中国四川盆地一座极易受复杂污染影响的特大城市——成都实测的VOC浓度校正为光化学初始浓度（PICs）。在本研究中，对光化学评估监测站（PAMS）目标清单上的56种VOC物种进行了四季全时段的定量监测。与直接测量值相比，VOCs的光化学初始化总混合比总体上增加了18.6%。烯烃和芳烃的光化学损失率在夏季（分别为68.6%、28.7%）和春季（分别为65.9%、24.7%）最为显著。此外，我们根据PICs研究了VOCs对大气氧化能力（AOC）的贡献，发现日最大总AOC在春季和夏季出现激增。除了羟基自由基外，春季的白天O和夏季傍晚的硝酸根自由基对于基于PICs的AOC至关重要。不出所料，烯烃和芳烃在基于PICs的臭氧生成潜势（OFPs）中占主导地位。此外，烯烃对二次有机气溶胶生成潜势的贡献在春季和夏季分别达到15.5%和7.6%。使用正定矩阵因子分解模型，我们识别出了包括机动车尾气、工业排放、溶剂使用、生物源以及液化石油气/天然气使用在内的5种VOC来源。基于PICs，生物源在春季和夏季被显著低估。同时，来自溶剂使用的间、对二甲苯和来自生物源的异戊二烯是OFPs的主要贡献者。因此，这些结果强调了光化学氧化的VOC浓度的重要性，特别是对于典型季节中的活性物种。
