Abstract View
Partitioning of Ambient Organic Gases to Inorganic Salt Solutions: Influence of Salt Identity, Ionic Strength, and pH
VIKRAM PRATAP, Annmarie Carlton, Amy Christiansen, Christopher Hennigan, University of Maryland, Baltimore County
Abstract Number: 50
Working Group: Aerosol Chemistry
Abstract
Inorganic salts can enhance (“salting-in”) or inhibit (“salting-out”) the partitioning of organic gases to aqueous solutions relative to that in pure water. These phenomena may affect the composition and abundance of secondary organic aerosol (SOA), though their importance in the atmosphere is largely unconstrained at present. In this work, we quantify the effects of salt identity, salt concentration (ionic strength), and solution pH on the partitioning of atmospheric water-soluble organic gases (WSOCg) at a site in the eastern United States. Experiments were conducted in a custom-made dual mist chamber setup where simultaneous measurements were conducted in two mist chambers – one filled with deionized water and other with the salt solution. This enabled a direct comparison of dissolved WSOCg in either chamber to estimate the salting effect of a salt. The experimental pH (pH = 1 – 6) and ionic strengths (10-3 – 101 mol kg-1) span a wide range of conditions found in atmospheric particles, clouds, and fog droplets. Chloride salts (NaCl, NH4Cl, and KCl) exhibit a strong salting-out effect at all ionic strengths > 0.005 mol kg-1 and pH = 1.8 – 6. Conversely, sulfate salts (Na2SO4, (NH4)2SO4, and K2SO4) induce both salting-in and salting-out behaviors, depending on ionic strength and pH. These results suggest that monovalent cations have a minimal effect on the partitioning behavior of ambient organic gases, while both ionic strength and pH exert important influences on the distribution of organics in the atmosphere.