Low molecular weight carboxylic acids in an urban atmosphere: Winter measurements in São Paulo City, Brazil
Low molecular weight carboxylic acids in an urban atmosphere: Winter measurements in São Paulo City, Brazil
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DOI：
10.1016/s1352-2310(98)00383-5
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发表时间：
1999-07
影响因子：
5
通讯作者：
S. R. Souza;P. Vasconcellos;L. Carvalho
中科院分区：
文献类型：
--
作者：
S. R. Souza;P. Vasconcellos;L. Carvalho
1996年7月冬季期间，在严重污染的拉丁美洲城市<s:1>圣保罗市区测量了大气气体和颗粒相羧酸。采用离子色谱和毛细管电泳技术进行了种类鉴定。在气溶胶颗粒中测定草酸（36.2±21.4%）、丙酮酸（15.0±7.9%）、β-羟基丁酸（9.15±9.00%）和乙醇酸（3.55±2.26%），在气相（分别为4.36±2.70和3.66±2.63ppbv）和颗粒相（分别为17.8±12.4和18.2±9.8%）中测定甲酸和乙酸。大约98%的乙酸和甲酸处于气相，气-气溶胶平衡受到高相对湿度的影响。气态甲酸与乙酸的比值在0.94-1.85之间下降。光化学生产似乎是本次调查中发现的气态乙酸和甲酸水平的一个很可能的来源。直接排放，主要是汽车尾气，也导致了它们在空气中的存在。在颗粒相中观察到的甲酸和乙酸的量与在其他城市站点中观察到的量相当。气溶胶颗粒的结果表明，夜间羧酸浓度较低，但其昼夜变化相似。利用相关矩阵，可以提出颗粒相中羧酸的一些来源。在白天，车辆排放似乎是乙酸的主要来源，而甲酸和丙酮酸则应形成光化学。此外，生物原生源的排放似乎是大气中甲酸和乙醇酸浓度的重要贡献。据推测，丙酮酸和乙醇酸的光氧化作用产生了草酸。夜间没有醋酸和丙酮酸的来源。然而，在夜间测量中，直接车辆和生物排放可能是TOC的主要来源。草酸可能来自车辆排放，乙醇酸可能来自生物源排放，甲酸可能来自两种来源。
Atmospheric gas and particle-phase carboxylic acids were measured during July 1996, Winter, in an urban area of São Paulo, a highly polluted Latin American city. Ion chromatography and capillary electrophoresis techniques were used to determine the species. As oxalic (36.2±21.4%), pyruvic (15.0±7.9%), β-hydroxy-butyric (9.15±9.00%) and glycolic (3.55±2.26%) acids were determined in aerosol particles, formic and acetic acids were determined both in the gaseous (4.36±2.70 and 3.66±2.63ppbv, respectively) and particulate phases (17.8±12.4 and 18.2±9.8%, respectively). Approximately 98% of the total acetic and formic acids were in the gas-phase and the gas–aerosol equilibrium was influenced by high levels of relative humidity. Gaseous formic-to-acetic ratios fell in the 0.94–1.85 range. Photochemical production appeared to be a very likely source of the gaseous acetic and formic acid levels found in this investigation. Direct emissions, mainly motor exhaust of vehicles also contributed to their presence in air. The observed amounts of formic and acetic acids in the particle phase were comparable with those observed in other urban sites. Results from aerosol particles indicated lower concentrations of the carboxylic acids at night, but their diurnal and nocturnal variation were similar. Using a correlation matrix, it was possible to suggest some sources for the carboxylic acids in the particulate phase. During daytime, vehicular emission appeared to be the primary source of acetic acid, whereas formic and pyruvic acids should be formed photochemically. Moreover, emissions from biogenic primary sources appeared to be an important contribution to atmospheric concentrations of formic and glycolic acids. Presumably, the photooxidation of pyruvic and glycolic acids gave rise to the oxalic acid. No source for acetic and pyruvic acids at nighttime was possible to suggest. However, direct vehicular and biogenic emissions might be major sources of TOC in nocturnal measurements. Oxalic acid might result from vehicular emission, glycolic acid from biogenic emission and formic acid from both sources.