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

California Institute Of Technology, Pasadena CA

Investigators

Abstract

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.