Atmospheric aerosol particles influence climate through their direct and indirect effects. These impacts are dependent on the morphology of the particles, which is determined by their composition and environment. The effect of pH on morphology was investigated using particles composed of 3-methylglutaric acid and ammonium sulfate by manipulating the starting pH of the bulk solution through addition of aqueous sodium hydroxide. The target pHs are located below pKa1, above pKa2, and between both pKas of 3-methylglutaric acid. The phase transitions, efflorescence, deliquescence, phase separation, and the mixing, were observed with optical microscopy. Due to changes in its protonation states, the solubility of the organic component increases with increasing pH, which shifts the location of separation relative humidity (SRH) to lower values. This shift in the SRH causes a hysteresis between the SRH and mixing relative humidity (MRH). We observe that pH has the greatest effect on the phase transitions that require nucleus formation, efflorescence and separation relative humidities, rather than deliquescence and mixing relative humidities.

pH Dependence of liquid-liquid phase separation in mixed organic-inorganic particles

252nd National Meeting (2016)

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