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Hygroscopic growth is one of the most fundamental properties of atmospheric aerosols. By absorbing or evaporating water, an aerosol particle changes its size, morphology, phase, chemical composition and reactivity and other parameters such as its refractive index. These changes affect the fate and the environmental impacts of atmospheric aerosols, including global climate change. The ElectroDynamic Balance (EDB) has been widely accepted as a unique tool for measuring hygroscopic properties and for investigating phase transformation of aerosols via single particle levitation. Coupled with Raman spectroscopy, an EDB/Raman system is a powerful tool that can be used to investigate both physical and chemical changes associated with the hygroscopic properties of individually levitated particles under controlled environments. In this paper, we report the use of an EDB/Raman system to investigate (1) contact ion pairs formation in supersaturated magnesium sulfate solutions; (2) phase transformation in ammonium nitrate/ammonium sulfate mixed particles; (3) hygroscopicity of organically coated inorganic aerosols; and (4) heterogeneous reactions altering the hygroscopicity of organic aerosols. [ABSTRACT FROM AUTHOR]

In this study, an electrodynamic balance (EDB) and a single particle Raman spectroscopic system were used to investigate the heterogeneous reactions of linoleic acid and linolenic acid with ozone under ambient temperatures (22−24 °C) and dry conditions (RH < 5%). Raman characterizations provide evidence that ozone-induced autoxidation, in addition to direct ozonolysis, is a plausible pathway in the reactions between ozone and linoleic acid and linolenic acid particles. Furthermore, the significance of this specific oxidation pathway depends on the ozone concentrations used in the experiment. A low ozone concentration (∼200−250 ppb) with a longer exposure period (20 h) favors autoxidation but an extremely high ozone concentration (∼10 ppm) favors ozonolysis and forces most unsaturated fatty acids to react with ozone in a relatively short period of time. In the low ozone concentration experiments, the mass of the ozone-processed linoleic acid and linolenic acid particles increased by about 2−3% and 10−13%, respectively. In addition, the mass ratios (particle mass at RH 85% to particle mass at RH < 5%) of the ozone-processed linoleic acid and linolenic acid particles increased by about 2−3% and 3−4%, respectively. The morphology of the pure and ozone-processed linoleic acid and linolenic acid particles are compared, based on imagining and their light scattering patterns. [ABSTRACT FROM AUTHOR]