Molecular composition of dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls and fatty acids in atmospheric aerosols from Tanzania, East Africa during wet and dry seasons
Molecular composition of dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls and fatty acids in atmospheric aerosols from Tanzania, East Africa during wet and dry seasons
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DOI：
10.5194/acp-13-2235-2013
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发表时间：
2012-09
影响因子：
6.3
通讯作者：
S. Mkoma;S. Mkoma;K. Kawamura
中科院分区：
文献类型：
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作者：
S. Mkoma;S. Mkoma;K. Kawamura
摘要。2011年湿季和旱季，在坦桑尼亚的一个农村地区收集了PM2.5和PM10的大气气溶胶样本，并使用气相色谱/火焰离子化检测器（GC/FID）和GC/质谱分析了水溶性二羧酸、酮羧酸、α-二羰基和脂肪酸。本文报道了湿季和旱季双酸及其相关化合物的分子组成和来源。在PM2.5和PM10中，草酸（C2）是最丰富的二酸，其次是琥珀酸和/或丙二酸，而乙醛酸和乙二醛分别是主要的酮酸和α-二羰基。雨季PM2.5中C2的平均浓度（121±47 ng m−3）低于旱季（258±69 ng m−3）。同样，雨季PM10样品的C2浓度（169±42 ng m−3）低于旱季（292±165 ng m−3）。C2在总二酸中相对丰度在干湿季节PM2.5中分别为65%和67%，在PM10中分别为65%和64%。坦桑尼亚的二酸（289-362 ng m - 3）、酮酸（37.8-53.7 ng m - 3）和α-二羰基（5.7-7.8 ng m - 3）的总浓度高于南非Nylsvley农村背景站点的报告，但与亚洲和欧洲站点的报告相当或更低。二酸和酮酸在两个季节都主要存在于PM2.5中（总α-二羰基在旱季），表明有机酸是由热原源和光化学氧化产生的。湿季总双酸对PM2.5和PM10的平均贡献分别为1.4%和2.1%，干季对PM2.5和PM10的平均贡献分别为3.3%和3.9%，而湿季对PM2.5和PM10水溶性有机碳的平均贡献分别为2.2%和4.7%，干季对PM10水溶性有机碳的平均贡献分别为3.1%和5.8%。旱季较高的比值表明，在强太阳辐射下，有机前体的光化学氧化可能通过气溶胶上的非均相反应而增强。在两个季节中，双酸及其相关化合物之间存在很强的正相关关系，并且与源示踪剂之间存在良好的关系，这表明天然生物源排放、生物质燃烧、生物燃料燃烧和光化学生产是混合源。
Abstract. Atmospheric aerosol samples of PM2.5 and PM10 were collected during the wet and dry seasons in 2011 from a rural site in Tanzania and analysed for water-soluble dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls, and fatty acids using a gas chromatography/flame ionization detector (GC/FID) and GC/mass spectrometry. Here we report the molecular composition and sources of diacids and related compounds for wet and dry seasons. Oxalic acid (C2) was found as the most abundant diacid species followed by succinic and/or malonic acids whereas glyoxylic acid and glyoxal were the dominant ketoacid and α-dicarbonyl, respectively in both seasons in PM2.5 and PM10. Mean concentration of C2 in PM2.5 (121 ± 47 ng m−3) was lower in wet season than dry season (258 ± 69 ng m−3). Similarly, PM10 samples showed lower concentration of C2 (169 ± 42 ng m−3) in wet season than dry season (292 ± 165 ng m−3). Relative abundances of C2 in total diacids were 65% and 67% in PM2.5 and 65% and 64% in PM10 in the wet and dry seasons, respectively. Total concentrations of diacids (289–362 ng m−3), ketoacids (37.8–53.7 ng m−3), and α-dicarbonyls (5.7–7.8 ng m−3) in Tanzania are higher than those reported at a rural background site in Nylsvley (South Africa) but comparable or lower than those reported from sites in Asia and Europe. Diacids and ketoacids were found to be present mainly in PM2.5 in both seasons (total α-dicarbonyls in the dry season), suggesting a production of organic acids from pyrogenic sources and photochemical oxidations. Averaged contributions of total diacids to aerosol total carbon were 1.4% in PM2.5 and 2.1% in PM10 during wet season and 3.3% in PM2.5 and 3.9% in PM10 during dry season whereas those to water-soluble organic carbon were 2.2% and 4.7% in PM2.5 during wet season and 3.1% and 5.8% in PM10 during dry season. The higher ratios in dry season suggest an enhanced photochemical oxidation of organic precursors probably via heterogeneous reactions on aerosols under strong solar radiation. Strong positive correlations were found among diacids and related compounds as well as good relations to source tracers in both seasons, suggesting a mixed source from natural biogenic emissions, biomass burning, biofuel combustion, and photochemical production.