Photochemical Cycling Between Humic-Like Substances and Simple Dicarbonylic Species in the Atmospheric Aerosol

大气气溶胶中有机物的物理状态和化学转化仍然是一个复杂的问题。大气化学家经常寻求识别和定量离散的低分子(MW)化合物，如碳氢化合物、脂类、脂肪酸和其他可识别的化合物类别。然而，这些成分的质量平衡往往低于许多气溶胶相中存在的总碳。气相痕量物质的原位光化学氧化形成有机气溶胶，它们随后在现有的空气悬浮颗粒上缩合，可能还会聚合，这是气溶胶和液滴中有机相积累的已知途径。有色生物聚合物广泛存在于土壤、水生和海洋环境中，与之类似的化合物也越来越多地在气溶胶系统中被研究。这些“类腐殖质”物质的光化学降解可能是在大气气溶胶系统中发现的复杂有机物质的另一种途径。基于对丙酮酸水相光解的初步实验室研究，加州理工学院的研究人员试图进一步研究在天然大分子物质存在下的二羧酸和氧羧酸的光交联，作为光化学循环类型的指示器，这可能是大气气溶胶中发现的一些较高分子量有机物的原因。

Both the physical state and the chemical transformations of organic matter in atmospheric aerosols remain a complex problem. Atmospheric chemists have often sought the identification and quantitation of discrete low molecular weight (MW) compounds such as hydrocarbons, lipids, fatty acids and other identifiable compound classes. However, a mass balance of these constituents often falls short of the total carbon present in many aerosol phases. Organic aerosol formation by in-situ photochemical oxidation of gas phase trace species, their subsequent condensation and perhaps polymerization on existing airborne particles is a known path for the accretion of organic phases in aerosols and droplets. Colored biogenic polymers are widespread in soils, aquatic and marine environments and compounds similar to these are also increasingly being studied in aerosol systems. Photochemical driven degradation of these ''humic-like'' substances may be another path to the complex organic substances found in atmospheric aerosol systems. Based on initial laboratory studies of the aqueous phase photolysis of pyruvic acid, Caltech investigators seek to further investigate the photocrosslinking of a-dicarbonylic and oxocarboxylic acids in the presence of natural macromolecular mater as indicators of the kinds of photochemical cycling which may be responsible for some of the higher molecular weight organic matter found in atmospheric aerosols.