Water-soluble organics in atmospheric particles: A critical review of the literature and application of thermodynamics to identify candidate compounds

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.

Evaluation of a Conceptual Model for Gas-Particle Partitioning of Polycyclic Aromatic Hydrocarbons Using Polyparameter Linear Free Energy Relationships

“…These compounds fall in the lower end of the molecular mass range for major WSOM constituents of PM proposed by Saxena and Hildemann. 47 Calculations showed that log K P values (m 3 air g −1 solvent ) for PYR and FLT determined using these ppLFER models (at 298 K, normalized using the solvent densities) differ by ≤0.3 and ≤0.1 log unit, respectively. We allocated DMSO-air to phase 'A' because it has both the highest water solubility (i.e., 1 × 10 6 compared to 2.19 × 10 5 and 9.78 × 10 5 mg L −1 , respectively; at 298 K) and Abraham "S" descriptor (1.72 compared to 0.70 and 1.31, respectively) and is the least volatile (p L 0 : 81.3 compared to 3.1 × 10 4 and 516 Pa, respectively) among the three candidate surrogates,…”

CCN closure study: Effects of aerosol chemical composition and mixing state

“…The Köhler theory provides a link between CCN activity and the hygroscopic growth of the aerosol. Because atmospheric aerosols are primarily complex mixtures of organics, inorganics, black carbon (BC), mineral dust, and sea salt, the multicomponent Köhler theory has been suggested to account for the effects of different solute species (mainly organics) on the surface tension [Saxena and Hildemann, 1996;Petters and Kreidenweis, 2007;Wang et al, 2010]. Various laboratory studies have investigated organic compounds and inorganic-organic mixtures to understand the differences in their activation behavior, which arises primarily due to solubility, droplet surface tension, and effects on the mass accommodation coefficient of water.…”

“…It is interesting to note that certain thermodynamically insoluble species also act as good CCN when present in metastable states or internally mixed with a small percentage of soluble species [Chang et al, 2007]. Although organics constitute a major portion of aerosols (10-70% of the submicron mass of the ambient aerosols), their formation mechanisms, detailed speciation, and roles in influencing the Earth's radiation budget are still not well understood [Saxena and Hildemann, 1996;Turpin et al, 2000;Hallquist et al, 2009;Kanakidou et al, 2005]. Recently, water-soluble organic compounds (WSOCs) have gained increased attention from researchers working on the indirect effect of aerosols.…”

“…Recently, water-soluble organic compounds (WSOCs) have gained increased attention from researchers working on the indirect effect of aerosols. WSOCs are classified into hydrophilic and hydrophobic fractions depending on the number of carbon atoms and functional groups attached having a solubility greater than 1 g/100 g water [Duarte and Duarte, 2005;Saxena and Hildemann, 1996]. Hydrophilic compounds (e.g., saccharides, amines, and aliphatic monocarboxylic/dicarboxylic/oxocarboxylic acids) have short carbon chain compared to hydrophobic compounds (e.g., phenols and aromatic acids) [Sullivan and Weber, 2006].…”

Estimation of water uptake by organic compounds in submicron aerosols measured during the Southeastern Aerosol and Visibility Study

“…Khwaja [1995] cites a long list of literature that supports the role of carboxylic acids, one of the dominant classes of organic compounds found in the atmosphere, in the precipitation acidity observed in both urban and remote areas of the world. Saxena and Hildemann [1996)] note that studies at both rural and urban locations have reported that approximately one fifth to two thirds of the total particulate carbon in the atmosphere consists of water soluble OC.…”