Comparison of dicarboxylic acids and related compounds in aerosol samples collected in Xi'an, China during haze and clean periods

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• 作者：Chunlei Cheng ; Gehui Wang ; Bianhong Zhou ; Jingjing Meng ; Jianjun Li ; Junji Cao ; Shun Xiao
• 关键词：PM10 ; Dicarboxylic acids ; Secondary organic aerosols ; Haze ; Formation mechanism
• 刊名：Atmospheric Environment
• 出版年：December, 2013
• 年：2013
• 卷：81
• 期：Complete
• 页码：443-449
• 全文大小：622 K

文摘

PM₁₀ aerosols from Xi'an, a mega city of China in winter and summer, 2009 were measured for secondary organic aerosols (SOA) (i.e., dicarboxylic acids (DCA), keto-carboxylic acids, and 伪-dicarbonyls), water-soluble organic (WSOC) and inorganic carbon (WSIC), elemental carbon (EC) and organic carbon (OC). Molecular compositions of SOA on haze and clean days in both seasons were compared to investigate their sources and formation mechanisms. DCA in the samples were 1843聽卤聽810聽ng聽m^鈭? in winter and 1259聽卤聽781聽ng聽m^鈭? in summer, respectively, which is similar and even higher than those measured in 2003. Oxalic acid (C₂, 1162聽卤聽570聽ng聽m^鈭? in winter and 1907聽卤聽707聽ng聽m^鈭? in summer) is the predominant species of DCA, followed by t-phthalic (tPh) in winter and phthalic (Ph) in summer. Such a molecular composition is different from those in other Asian cities where succinic acid (C₄) or malonic acid (C₃) is the second highest species, which is mostly due to significant emissions from household combustion of coal and open burning of waste material in Xi'an. Mass ratios of C₂/diacids, diacids/WSOC, WSOC/OC and individual diacid-C/WSOC are higher on the haze days than on the clean days in both seasons, suggesting an enhanced SOA production under the haze condition. We also found that the haze samples are acidic while the clean samples are almost neutral. Such a difference in particle acidity is consistent with the enhanced SOA production, because acid-catalysis is an important aqueous-phase formation pathway of SOA. Gly/mGly mass ratio showed higher values on haze days than on clean day in both seasons. We comprehensively investigated the ratio in literature and found a consistent pattern. Based on our observation results and those documented data we proposed for the first time that concentration ratio of Gly/mGly can be taken as an indicator of aerosol ageing.