Depositional ice nucleation on atmospheric aerosols has been identified as a potential pathway for cirrus cloud formation. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both sulfates and organics. While ammonium sulfate is an efficient depositional ice nucleus, the role of organics remains largely uncertain. To explore this role, we used Raman microscopy to study several phase-separated organic�ammonium sulfate mixtures from 210-235 K. Raman mapping indicates that these particles contain ammonium sulfate cores fully engulfed in organic shells. For the ice nucleation experiments, we find that if the organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium sulfate core. Here, the coatings minimally affect the ice nucleation efficiency of ammonium sulfate. In contrast, if the coatings become glassy, ice instead nucleates on the organic shell. These coatings alter the ice nucleation efficiency of ammonium sulfate.

Ice nucleation on phase separated particles: Effect of liquid vs. glassy coatings

244th National Meeting (2012)

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