Effects of Inorganic Salts and pH on the Gas-Water Partitioning of Formic Acid and Acetic Acid Observed using Mist Chambers

Abstract

Secondary organic aerosol (SOA) is harmful to human health and contributes largeuncertainties to climate forcing. Oxygenated volatile organic compounds (OVOCs), such as carboxylic acids, make significant contributions to SOA by partitioning to atmospheric particulate and aqueous phases. Inorganic salt content and pH of atmospheric water can impact OVOC partitioning and therefore the composition and abundance of SOA. In this work, parallel sampling mist chambers (MC) coupled with wet chemical oxidation(WCO)-based total organic carbon (TOC) analysis is critically evaluated as a method for measuring effects from inorganic salts and pH on formic acid (FA) and acetic acid (AA) gas-water partitioning. High ionic concentrations of chloride (>0.01 mol kg -1 ) and sulfate (>0.1 mol kg -1 ) caused TOC measurement artifacts that required correction. Chloride concentrations characteristic to atmospheric aqueous phases exhibited a salting-out effect on FA and AA partitioning and partitioning to solutions of low pH was reduced. Sulfate did not show a stronginfluence over FA and AA partitioning. Preliminary experiments with glyoxal indicate no effects from chloride and sulfate on partitioning although salting-in effects are reported in literature. Options for further experimentation, validation, and optimization of the MC-WCO method are discussed.