The effect of surfactants on the deliquescence of sodium chloride.

This study investigated the deliquescence of sodium chloride aerosol with surfactants at a retention time of 4.24 sec. Two surfactants used in this study, glutaric acid and pyruvic acid, are found in atmospheric aerosol and have a high hydrophile-lipophile balance (HLB) value. The experimental system consisted of a relative humidity conditioner, a tandem differential mobility analyzer (TDMA) and a scanning mobility particle sizing (SMPS) system. Results obtained from the observation of TDMA presented the deliquescence point of sodium chloride aerosol at 75% RH. In addition, the growth size of sodium chloride aerosol was observed to be 79.47 nm and the growth ratio was 77.94%, when the initial size of aerosol was 101.82 nm. Surfactants were internally mixed with sodium chloride at six different weight fractions, i.e. 2.5, 5, 10, 20, 40, and 60% by weight of surfactants in dry aerosol. Both surfactants apparently decreased the deliquescence point of sodium chloride, in which the lowest deliquescence point appeared at about 71% RH when the weight fraction of surfactants is 60% by weight of surfactants in dry aerosol. Moreover, the smallest size of sodium chloride aerosol with surfactants was 142.7 nm at 60% by weight of pyruvic acid in dry aerosol. Our results further demonstrate that the deliquescence point and size of sodium chloride aerosol with surfactants are related to the weight fraction of surfactants.