Effect of Acidity and Liquid-Liquid Phase Separation on Heterogeneous Ice Nucleation
ZIYING LEI, Sarah Brooks,
Texas A&M University Abstract Number: 158
Working Group: Aerosol Physical Chemistry and Microphysics
AbstractAerosol Acidity plays a critical role in heterogeneous chemical reactions and human health, as well as potential impacts on climate by acting as cloud condensation nuclei (CCN) and ice nucleating particles (INPs). However, the effect of acidity on ice nucleation of inorganic and organic aerosols has not been addressed. Recently, studies found that liquid-liquid phase separation of aerosol particles is pH-dependent. The resulting morphology and phase state may, in turn, alter the aerosol’s ability to act as INPs.
In this study, our well-established ice nucleation technique combined with Raman micro-spectroscopy is used to study heterogeneous ice nucleation of representative inorganic and organic aerosols under a range of pH conditions (pH -0.1 to 5). Compounds include inorganic (e.g., ammonium sulfate), organic compounds (e.g., sucrose, diethyl sebacate, polyethylene glycol 400, 1,2,6-hexanetriol), and their mixtures. To investigate the potential roles of acidity and liquid-liquid phase separation on ice nucleation, the immersion freezing temperatures of 2 µL sample droplets containing varying amounts of sulfuric acid were determined.
Our results show that increased acidity reduced the ice nucleation ability of droplets containing sulfuric acid and inorganic-organic mixture. Using Raman spectroscopy, changes in the ratio of bisulfate to sulfate were observed to coincide with the changes in ice nucleation temperatures. Possible explanations for the observed changes in ice nucleation temperature are changes in the solubility of the organic component (related to sulfate protonation state), viscosity, and phase. This study aims to improve our fundamental understanding of the effect of acidity on phase separation and ice nucleation, which will lend context to the role of acidity and atmospheric ice cloud formation.