Chemical Transformations Involving Carbonyls and Carboxylic Acids Within Clouds

羰基化合物是臭氧的光化学前体，而羧酸是酸度的主要来源，因此在一定程度上控制了大气液滴中与pH有关的转化。尽管这类化合物在大气化学中具有公认的重要性，但在它们的生物地球化学循环过程中仍存在许多不确定性。拟议的调查将在农村地区首次同时测量气相和水相(云)中的羰基和有机酸。三个机构，每个机构都带来了特定领域的专业知识，将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国家公园的仪表塔(海拔1014米)进行的各种气象和气相和水相化学测量。将在1990年4月至5月期间进行为期一个月的密集实地采样，随后通过对云内化学和物理过程进行最先进的计算机模拟来促进对数据的解释。将审查同时观察到的羰基和有机酸，以寻找大气中将羰基氧化为有机酸的证据，特别关注作为甲酸来源的甲醛在云中的水相氧化。观察到的各化合物在气相和云水相之间的分馏将与热力学平衡中预期的分馏进行比较。将收集两个云滴大小分数，这将记录云水浓度与大小的关系。这项调查的结果将大大有助于我们了解决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.