Interactions of organosulfates with water vapor under sub- and supersaturated conditions

Abstract. Organosulfates (OSs) are important constituents of secondary organic aerosols, but their hygroscopic properties and cloud condensation nucleation (CCN) activities have not been well understood. In this work we employed three complementary techniques to characterize interactions several OSs with water vapor under sub- supersaturated conditions. A sorption analyzer was used measure mass changes in OS samples relative humidity (RH, 0 %–90 %); among the 11 organosulfates examined, only sodium methyl sulfate (methyl-OS), ethyl (ethyl-OS), octyl (octyl-OS) potassium hydroxyacetone were found deliquesce as RH increased, growth factors at 90 % determined be 3.65 ± 0.06, 3.58 0.02, 1.59 0.01 2.20 0.03. Hygroscopic methyl-, ethyl- octyl-OS aerosols also studied using a tandem differential mobility (H-TDMA); continuous observed, 1.83 0.03, 1.79 0.02 1.21 0.02. We further investigated CCN single hygroscopicity parameters (?ccn) 0.459 0.021, 0.397 0.010 0.206 0.008. For methyl- ethyl-OS ?ccn values agree reasonably those derived from H-TDMA measurements (?gf) differences being < 25 %, whereas ? 2.4 times larger than ?gf for octyl-OS, likely due both solubility limit surface tension reduction.