Determination of Sources of Atmospheric Organic Acids in Southern California by Carbon Isotope Measurements

9301767卡普兰大气有机酸在雨云酸化中起着重要作用。它们是城市烟雾和雾霾的普遍成分，存在于农村和基本上无人居住的地区(例如亚马逊雨林流域)的大气中。有机酸不仅有助于降低pH值，还可能通过吸附到“黑碳”上而导致能见度降低，而且由于它们的螯合能力，它们可能在腐蚀中发挥重要作用。已有研究表明，汽车通过不完全燃烧将甲酸、醋酸和草酸等有机酸排放到大气中。此外，生物质和工业产品的燃烧也可能产生有机酸，维管植物释放的有机酸可能是一个重要的生物来源。然而，目前几乎没有关于这些不同的人为和生物来源的有机酸排放速率的信息。这项研究项目将试图通过测量碳-14/碳-12和碳-13/碳-12等碳同位素比率来表征南加州城市和农村地区大气有机酸的来源。用加速器质谱仪测量碳-14/碳-12可以区分化石燃料成因碳和天然生物成因碳。碳-13/碳-12的测量可以确定大气有机酸形成的各种人为和自然来源以及动力学过程。为了完成这一项目，这些研究人员开发了使用离子排除色层析从大气湿样品中提取、分离和分离毫克量的单个有机酸的方法。在19993秋季至1995年冬季期间，将在洛杉矶及其周边农村地区收集大气潮湿样本，如雨、云、雾和露水以及气体和气溶胶样本。在这项研究中，还将对各种有机酸源进行采样，以确定其特定的同位素比率。将这些特定来源的同位素比值数据与大气样品的同位素数据进行比较，以确定这些样品中有机酸的不同来源。根据《国家清洁空气法》的建议，确定这些大气有机酸的具体来源将有助于未来控制洛杉矶和其他地方的酸沉积和空气污染问题的战略。

9301767 Kaplan Atmospheric organic acids play an important role in acidification of rain and clouds. They are ubiquitous constituents of urban smog and haze and are present in the atmosphere of rural and largely uninhabited areas (e.g. the Amazon Rain Forest Basin). Organic acids not only contribute to lowering pH, they may contribute to visibility reduction by being adsorbed to "black carbon" and they may play an important role in corrosion due to their chelating ability. It has been shown that organic acids such as formic, acetic, and oxalic acids are emitted into the atmosphere by automobiles through incomplete combustion. Additionally, combustion of biomass and industrial products may also generate organic acids and their release from vascular plants may be an important biogenic source. Little information is, however, currently available on the emission rates of organic acids from these various anthropogenic and biogenic sources. This research project will attempt to characterize the sources of atmospheric organic acids in urban and rural areas of southern California by measurements of their carbon isotopic ratios, such as carbon- 14/carbon-12 and carbon-13/carbon-12. The carbon-14/carbon-12 measurements by accelerator mass spectrometry can differentiate fossil fuel-origin carbons form natural biogenic carbons. The measurements of carbon-13/carbon-12 can identify various anthropogenic and natural sources as well as kinetic processes in the formation of atmospheric organic acids. To accomplish this project these researchers have developed methodologies using ion exclusion chromatography to extract, separate, and isolate milligram quantities of individual organic acids form atmospheric wet samples. During Fall 19993 to Winter 1995, atmospheric wet samples such as rain, clouds, fog and dew as well as gas and aerosol simples will be collected in Los Angeles and its surrounding rural vicinity. Various organic acid-emitting sources will also be sampled in this study to determine their specific isotopic ratios. These source-specific isotopic ratio data will be compared to the isotopic data of atmospheric samples, in order to identify the different sources of the organic acids in there samples. The identification of specific sources for these atmospheric organic acids will contribute to future control strategies for acidic deposition and air pollution problems in Los Angeles and elsewhere as proposed by the National Clean Air Act.