Changes of fatty acid aerosol hygroscopicity induced by ozonolysis under humid conditions
Changes of fatty acid aerosol hygroscopicity induced by ozonolysis under humid conditions
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潮湿条件下臭氧分解引起的脂肪酸气溶胶吸湿性的变化
DOI：
10.5194/acp-8-4683-2008
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发表时间：
2007
影响因子：
6.3
通讯作者：
M. Ammann
中科院分区：
文献类型：
--
作者：
O. Vesna;S. Sjogren;E. Weingartner;V. Samburova;M. Kalberer;H. Gäggeler;M. Ammann
不饱和脂肪酸是来自生物来源或燃烧来源的大气气溶胶有机组分的重要成分。这些物质的氧化处理可能会改变它们与水的相互作用，从而影响它们对气候的影响。在流动反应器中研究了油酸和花生四烯酸气溶胶颗粒在潮湿条件下的臭氧分解，臭氧暴露在接近大气水平，浓度在0.5ppm到2ppm之间。油酸是这类研究的广泛使用的替代品，而花生四烯酸代表多不饱和脂肪酸，可能会分解成吸湿性产物。在臭氧氧化过程中，随着相对湿度的增加，氧化花生四烯类颗粒在93%相对湿度(RH)下的吸湿性(直径)生长因子增加到1.09。相比之下，油酸的生长因子很低(在93%RH下为1.03)，且几乎不受臭氧氧化条件的影响，因此油酸不是观察大气条件下氧化诱导吸湿性变化的良好模型。对于花生四烯酸颗粒，我们发现在臭氧氧化过程中，湿度引起的吸湿性变化伴随着羧酸质子与脂肪族质子的比率增加约一倍。我们认为，在潮湿的条件下，水与Criegee中间体的反应可能会打开一条形成较小酸的途径，从而导致吸湿性发生更显著的变化。因此，在本研究中观察到的水在臭氧分解过程中提供竞争途径的效果应该是在未来与气溶胶颗粒老化相关的研究中包括水的动机，水普遍存在于大气颗粒及其周围。
Unsaturated fatty acids are important constituents of the organic fraction of atmospheric aerosols originating from biogenic or combustion sources. Oxidative processing of these may change their interaction with water and thus affect their effect on climate. The ozonolysis of oleic and arachidonic acid aerosol particles was studied under humid conditions in a flow reactor at ozone exposures close to atmospheric levels, at concentrations between 0.5 and 2 ppm. While oleic acid is a widely used proxy for such studies, arachidonic acid represents polyunsaturated fatty acids, which may decompose into hygroscopic products. The hygroscopic (diameter) growth factor at 93% relative humidity (RH) of the oxidized arachidonic particles increased up to 1.09 with increasing RH during the ozonolysis. In contrast, the growth factor of oleic acid was very low (1.03 at 93% RH) and was almost invariant to the ozonolysis conditions, so that oleic acid is not a good model to observe oxidation induced changes of hygroscopicity under atmospheric conditions. We show for arachidonic acid particles that the hygroscopic changes induced by humidity during ozonolysis are accompanied by about a doubling of the ratio of carboxylic acid protons to aliphatic protons. We suggest that, under humid conditions, the reaction of water with the Criegee intermediates might open a pathway for the formation of smaller acids that lead to more significant changes in hygroscopicity. Thus the effect of water to provide a competing pathway during ozonolysis observed in this study should be motivation to include water, which is ubiquitously present in and around atmospheric particles, in future studies related to aerosol particle aging.