Water-soluble organics in atmospheric particles: A critical review of the literature and application of thermodynamics to identify candidate compounds |
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| Authors: | Pradeep Saxena Lynn M Hildemann |
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| Institution: | (1) Environmental and Water Studies Program, Department of Civil Engineering, Stanford University, 94305-4020 Stanford, CA, U.S.A.;(2) Present address: Electric Power Research Institute, Palo Alto, California |
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| Abstract: | Although organic compounds typically constitute a substantial fraction of the fine particulate matter (PM) in the atmosphere, their molecular composition remains poorly characterized. This is largely because atmospheric particles contain a myriad of diverse organic compounds, not all of which extract in a single solvent or elute through a gas chromatograph; therefore, a substantial portion typically remains unanalyzed. Most often the chemical analysis is performed on a fraction that extracts in organic solvents such as benzene, ether or hexane; consequently, information on the molecular composition of the water-soluble fraction is particularly sparse and incomplete.This paper investigates theoretically the characteristics of the water-soluble fraction by splicing together various strands of information from the literature. We identify specific compounds that are likely to contribute to the water-soluble fraction by juxtaposing observations regarding the extraction characteristics and the molecular composition of atmospheric particulate organics with compound-specific solubility and condensibility for a wide variety of organics. The results show that water-soluble organics, which constitute a substantial fraction of the total organic mass, include C2 to C7 multifunctional compounds (e.g., diacids, polyols, amino acids). The importance of diacids is already recognized; our results provide an impetus for new experiments to establish the atmospheric concentrations and sources of polyols, amino acids and other oxygenated multifunctional compounds. |
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| Keywords: | organic particle composition water-soluble organics hygroscopic organics Henry's law constants organic solubility polyols multifunctional compounds |
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