Hygroscopic properties of mixed ammonium sulfate and carboxylic acids particles

The hygroscopic growth of internally mixed ammonium sulfate and carboxylic acid particles was measured as a function of relative humidity by using a tandem differential mobility analyzer (TDMA). In TDAM experiments the organic compounds with different solubilities act in several ways, ranging from the behavior of totally insoluble substance to that of soluble compounds. The hygroscopic properties for mixtures containing either adipic acid or phthalic acid together with ammonium sulfate indicate that the organic fraction of the particles behaves as an inert mass and does not contribute to water uptake. The mixtures involving malonic acid or succinic acid increased the water uptake of the ammonium sulfate part only. The results indicate that the solubility of the organic fraction in individual aerosol particles clearly influences the aerosol-water interaction.