Deliquescence and hygroscopic growth of mixed inorganic - Organic atmospheric aerosol

Abstract

Deliquescence and hygroscopic growth measurements were performed for four internally mixed aerosol mixtures: NaCl-glutaric acid, NaCl-pinonic acid, (NH4)2SO4-glutaric acid, and (NH4)2SO4-pinonic acid with varying organic mass fractions (0, 0.2, 0.5, 0.8, and 1.0). No effect on the deliquescence relative humidity of the salts was observed for any of the organic mixtures tested. The NaCl-organic mixed aerosols deliquesced at a relative humidity (DRH) 75 ± 1% and the (NH4)2SO4-organic aerosol at 79 ± 1% independent of organic mass fraction. The growth factors at RH = 85 ± 1%, G(85%), were also measured for the different aerosol mixtures. There was an observed decrease in G(85%) with increasing mass fraction of the organic. Measured G(85%) for the mixtures can be approximated as a first step with the assumption that the species absorb water independently. Overall, the organic portion was observed to enhance the water uptake of the (NH4)2SO4-organic aerosol systems by as much as a factor of 2-3 for particles consisting of 80% organic acids. The NaCl-organic mixtures presented evidence of positive and negative interaction depending on organic mass fraction, ranging from a 40% decrease to an 20% increase in water uptake as compared to that by the inorganic fraction alone.