AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Effect of Different Atmospherically Relevant Salts and Salt Mixtures on Aqueous Phase Partitioning of Organic Vapors
CHEN WANG, Ying Duan Lei, Frank Wania, University of Toronto
Abstract Number: 197 Working Group: Aerosol Chemistry
Abstract Dissolved inorganic salt(s) influence the partitioning of organic compounds into the aqueous phase. This influence is especially significant in atmospheric aerosol, which usually contains highly concentrated solutions of various ions, including sodium, ammonium, chloride, sulfate and nitrate. These ions originate from both natural (e.g. sodium chloride from sea spray) and anthropogenic sources (e.g. nitrate and sulfate from NO$_X and SO$_2). However, empirical data on this salt effect are very sparse in the literature. Since it is very difficult to quantify the contribution of individual ions, salting constants are typically only measured for combined salts. In this study, the partitioning of numerous organic compounds into solutions of Na$_(2)SO$_(4), NH$_(4)NO$_(3), and NH$_4Cl was measured and compared with existing data for NaCl and (NH$_(4))$_(2)SO$_(4). Salt mixtures were also tested in order to establish whether the salt effect is additive. In general the salt effect for various ion combinations showed a trend of Na$_(2)SO$_(4)> (NH$_(4))$_(2)SO$_(4) > NaCl > NH$_(4)Cl > NH$_(4)NO$_(3) for the studied organic compounds. This implies the following relative strength of the salt effect of individual anions: SO$_(4)$^(2-) > Cl$^(-) > NO$_(3)$^(-) and cations: Na$^(+) > NH$_(4)$^(+). The salt effect of different salts is moderately correlated. Data obtained in this study can be used for predictive model development. The experimental data indicate that the salt effect of mixtures may not be entirely additive. However, the deviation from additivity, if it exists, is small. Data of very high quality are required to establish whether the effect of constituent ions or salts is additive or not.