Hygroscopic behavior of atmospherically relevant water-soluble carboxylic salts and their influence on the water uptake of ammonium sulfate

摘要

The hygroscopic behavior of atmospherically relevant water-solublecarboxylic salts and their effects on ammonium sulfate were investigatedusing a hygroscopicity tandem differential mobility analyzer (H-TDMA). Nohygroscopic growth is observed for disodium oxalate, while ammonium oxalateshows slight growth (growth factor = 1.05 at 90%). The growth factors at90% RH for sodium acetate, disodium malonate, disodium succinate,disodium tartrate, diammonium tartrate, sodium pyruvate, disodium maleate,and humic acid sodium salt are 1.79, 1.78, 1.69, 1.54, 1.29, 1.70, 1.78, and1.19, respectively. The hygroscopic growth of mixtures of organic salts withammonium sulfate, which are prepared as surrogates of atmospheric aerosols,was determined. A clear shift in deliquescence relative humidity to lower RHwith increasing organic mass fraction was observed for these mixtures. Above80% RH, the contribution to water uptake by the organic salts was close tothat of ammonium sulfate for the majority of investigated compounds. Theobserved hygroscopic growth of the mixed particles at RH above thedeliquescence relative humidity of ammonium sulfate agreed well with thatpredicted using the Zdanovskii-Stokes-Robinson (ZSR) mixing rule. Mixturesof ammonium sulfate with organic salts are more hygroscopic than mixtureswith organic acids, indicating that neutralization by gas-phase ammoniaand/or association with cations of dicarbonxylic acids may enhance thehygroscopicity of the atmospheric particles.