Abstract
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 of several OSs with water vapor under sub- and supersaturated conditions. A vapor sorption analyzer was used to measure mass changes in OS samples with relative humidity (RH, 0 %–90 %); among the 11 organosulfates examined, only sodium methyl sulfate (methyl-OS), sodium ethyl sulfate (ethyl-OS), sodium octyl sulfate (octyl-OS) and potassium hydroxyacetone sulfate were found to deliquesce as RH increased, and their mass growth factors at 90 % RH were determined to be 3.65 ± 0.06, 3.58 ± 0.02, 1.59 ± 0.01 and 2.20 ± 0.03. Hygroscopic growth of methyl-, ethyl- and octyl-OS aerosols was also studied using a humidity tandem differential mobility analyzer (H-TDMA); continuous hygroscopic growth was observed, and their growth factors at 90 % RH were determined to be 1.83 ± 0.03, 1.79 ± 0.02 and 1.21 ± 0.02. We further investigated CCN activities of methyl-, ethyl- and octyl-OS aerosols, and their single hygroscopicity parameters (κccn) were determined to be 0.459 ± 0.021, 0.397 ± 0.010 and 0.206 ± 0.008. For methyl- and ethyl-OS aerosols, κccn values agree reasonably well with those derived from H-TDMA measurements (κgf) with relative differences being < 25 %, whereas κccn was found to be ∼ 2.4 times larger than κgf for octyl-OS, likely due to both the solubility limit and surface tension reduction.
Highlights
Secondary organic aerosols (SOA) contribute approximately 70 % to the global atmospheric organic aerosols (Hallquist et al, 2009; Jimenez et al, 2009)
The mass of ethyl-OS was moderately increased when relative humidity (RH) was increased from 40 % to 50 %, and a further increase in RH to 60 % led to an additional small increase in sample mass; the increase in sample mass at 50 % and 60 % RH may be because ethylOSs were partially deliquesced at this stage (Ling and Chan, 2008; Mikhailov et al, 2009)
90 1.59 ± 0.01 7.63 ± 0.02 2.20 ± 0.03 12.84 ± 0.18 tion that occasionally small increase in sample mass was observed for a few samples when RH was increased from 80 % to 90 %, and such small increase in sample mass may be caused by water uptake of impurities contained in these synthesized compounds
Summary
Secondary organic aerosols (SOA) contribute approximately 70 % to the global atmospheric organic aerosols (Hallquist et al, 2009; Jimenez et al, 2009). Hygroscopic growth (change in mobility diameters) and CCN activation of submicron aerosol particles were studied for sodium methyl sulfate, sodium ethyl sulfate and sodium octyl sulfate, using a humidity tandem differential mobility analyzer (H-TDMA) and a cloud condensation nuclei counter (CCNc). Due to their very limited quantities, we could not carry out H-TDMA and CCNc measurements for other OS samples which were synthesized by us. We investigated the impacts of sodium methyl sulfate, sodium ethyl sulfate and sodium octyl sulfate on hygroscopic properties and CCN activities of ammonium sulfate
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