Add time:09/10/2019         Source:sciencedirect.com

The chemical and physical properties of secondary organic aerosol (SOA) may be influenced by the aqueous environment within which SOA-forming reactions occur. Bulk-phase reactions between glyoxal and ammonium sulfate produce light-absorbing compounds such as imidazole-2-carboxaldehyde (IC) and biimidazole (BI) and model aerosol-phase chemistry. The effect of solvent composition on IC and BI production kinetics were examined for solutions containing a series of short-chain alcohols (methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, tert-butanol, and 3-methyl-2-butanol), as functions of the species and concentration added. The addition of an alcohol likely altered the solvent by inducing the formation of micro-heterogeneities of hydrated alcohol molecules. An increased alcohol concentration in solution resulted in a general increase in the production of IC and BI, with ethanol and the secondary alcohols causing the largest changes. The rate constants for IC and BI production in solutions that do not contain alcohol are found to be (4.03 ± 2.02) x 10−6 s−1 and (3.48 ± 1.75) x 10−6 s−1, respectively. In solutions that do contain an alcohol, rate constant values range from 3.23 × 10−6 s−1 to 6.61 × 10−6 s−1 for IC and 0.985 × 10−6 s−1 to 6.87 × 10−6 s−1 for BI, depending on the alcohol and the concentration. While these prevailing trends of more alcohol in solution leading to amplified production of imidazoles were observed for all seven alcohols, the diversity of responses implies the mode of action depends strongly on the species of alcohol added. Properties that describe a solution in bulk, such as dielectric constant, are not found to be reliable predictors of subsequent system behavior. Solvent composition influences SOA chemistry, and interactions between relevant functional groups within solution drive this influence, which suggests the importance of understanding individual relationships between aerosol-phase chemicals and SOA properties and production.

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