Heterogeneous ice nucleation on solid ammonium sulfate and solid amorphous glutaric acid particles was studied using optical microscopy and Raman spectroscopy. Optical microscopy was used to detect selective nucleation events as water vapor was slowly introduced into an environmental sample cell. Particles that nucleated ice were dried via sublimation and examined in detail using Raman spectroscopy. Depositional ice nucleation occurred preferentially on just a few ammonium sulfate and glutaric acid particles in each sample. For freezing temperatures between 214 K and 235K average ice saturation ratios of S=1.10±0.07 for solid ammonium sulfate and S=1.39±0.16 for solid amorphous glutaric acid particles were determined. Experiments with externally mixed particles further show that ammonium sulfate is a more potent ice nucleus that glutaric acid. Our results suggest that heterogeneous nucleation on ammonium sulfate may be an important pathway for atmospheric ice nucleation and cirrus cloud formation when solid aerosol particles are available for ice formation. This pathway for ice formation may be particularly significant near the tropopause region where sulfates are abundant and other species known to be good ice nuclei are depleted.
Baustian, K. J.; Wise, M. E.; and Tolbert, M. A., "Depositional Ice Nucleation on Solid Ammonium Sulfate and Glutaric Acid Particles" (2009). Faculty Research. 59.