Chemical Transformation Involving Carbonyls and Carboxylic Acids Within Clouds

羰基化合物是臭氧的光化学前体，而羧酸是酸性的主要来源，因此在一定程度上控制着大气液滴中依赖pH的转化。尽管人们认识到这类化合物在大气化学中的重要性，但它们的生物地球化学循环过程存在许多不确定性。拟议的调查将提供第一个在农村地区同时进行的羰基和有机酸的气相和水相（云）测量。三家机构将各自带来特定领域的专业知识，对涉及这些化合物的云内化学转化进行详细研究。这项调查将使用位于弗吉尼亚州谢南多厄国家公园的仪器塔（海拔1014米）进行各种气象、蒸汽和水相化学测量。将在1990年4月至5月的一个月期间内进行密集的实地抽样，稍后将利用最先进的云内化学和物理过程计算机模型对数据进行解释。对羰基和有机酸的同时观察将检查羰基氧化为有机酸的大气证据，特别关注云内水相氧化甲醛作为甲酸的来源。观察到的单个化合物在气相和云水相之间的分馏将与热力学平衡所期望的分馏进行比较。将收集两个云滴大小的分数，这将记录大小依赖于云水浓度。这项调查的结果将大大有助于我们了解确定对流层化学成分的重要过程。

Carbonyl compounds are photochemical precursors of ozone while carboxylic acids are major sources of acidity and therefore control in part pH dependent transformations in atmospheric droplets. Despite the recognized importance of these classes of compounds in atmospheric chemistry, much uncertainty exists concerning processes in their biogeochemical cycling. The proposed investigation will provide the first concurrent gas-phase and aqueous-phase (cloud) measurements of carbonyls and organic acids at a rural site. Three institutions, each bringing expertise in specific fields will perform a detailed study of in-cloud chemical transformations involving these compounds. This investigation will employ various meteorological and vapor- and aqueous-phase chemical measurements from an instrumented tower (1014 m elevation) situated in the Shenandoah National Park, Virginia. Intensive field sampling will be conducted over a one month period in April-May 1990, with later interpretation of the data facilitated by state-of-the-art computer modeling of in-cloud chemical and physical processes. The concurrent observations of carbonyls and organic acids will be examined for evidence of atmospheric oxidation of carbonyls to organic acids, with special focus on the in-cloud aqueous-phase oxidation of formaldehyde as a source of formic acid. The observed fractionations of individual compounds between the gas phase and the cloudwater phase will be compared to those expected from thermodynamic equilibrium. Two cloud droplet size fractions will be collected, which will document the size dependence of cloudwater concentrations. The results of this investigation will contribute substantially to our knowledge of important processes determining the chemical composition of the troposphere.