Relationship between Structure, Functionality, and Viscosity for Aerosol-Mimicking Solutions Containing Ammonium Sulfate, Glyoxal, and a Series of Oxidized C₁–C₅ Compounds

Abstract

The physical properties of aqueous secondary organic aerosol (SOA) can be influenced by the chemical composition of the solvent matrix within which SOA-forming reactions take place. The chemical structure and functionality of perturbing solutes on solution viscosity in bulk-phase SOA-modeling reaction mixtures containing glyoxal and ammonium sulfate were measured for a series of oxidized C1–C5 compounds. In general, as the solute concentration increased, solution viscosity increased, with the magnitude of those increases dependent upon the solute species added. The presence of glyoxal increased viscosity in about 50% of mixtures as a result of specific solute/solvent/product interactions. The oxygen/carbon (O/C) ratio was found to have a linear relationship with relative viscosity at a high solute concentration such that every −CH2CH2OH moiety addition increased solution viscosity by 25%. Solutes with identical O/C ratios but different structural characteristics (for example, acetone, 1-propanol, and 2-propanol) showed 7–8% differences in viscosity as a function of the chain length or ability to act as a hydrogen bond donor. The addition of an alcohol group increased viscosity by 10–20% over hydrogen or methyl groups in the same position. The solute structure appears to play a role in mediating intrasolvent interactions, and increases in hydrogen bonding and intersolute interactions lead to increased bulk solution viscosity, as shown in a series of experiments varying the timing and order of solute addition. These solutes are models for oxidized aerosol components, and the structure-dependent results suggest the importance of the aqueous layer functional group presence on aerosol physical properties, such as viscosity.

Virtual Special Issue: New Advances in Organic Aerosol Chemistry

“…Beier and co-workers report a dramatic surface tension decrease of brown carbon mixtures under photooxidation . Gubbins et al demonstrated that adding alcohols to glyoxal–ammonium sulfate solutions known to form light-absorbing organics increases the viscosity of the mixture with an increasing concentration and O:C ratio . DeRieux et al and De Haan et al both investigate the interplay between aerosol phase state and in-particle brown carbon formation by reactions of amines.…”