Seminar Speakers: Professors Miriam Freedman, Chemistry-Penn State University and Jerry Harrington, Meteorology

Mineral dust and biological particle influences on ice nucleation and vapor growth 

Ice formation and growth are often treated as separate processes even though these processes are likely linked together. Our laboratory experiments on immersion freezing reveal the impact of solutes on the ice nucleation activity of mineral dust and biological particles.  Specifically, ammonium-based solutes increase the ice nucleation activity of kaolinite minerals at low concentrations.  Ammonium salts at higher concentrations as well as all other solutes decrease the ice nucleation activity of kaolinite, but do not match expectations from freezing point depression calculations.  For biological ice nuclei, all solutes decrease the ice nucleation activity.  In this case, a constant trend is observed with respect to freezing point depression.  These studies give insight into the impact of internally mixed aerosol on ice nucleation in the atmosphere. 

Ice crystal growth experiments in our levitation diffusion chamber show that the growth rates of small crystals depend on the state of the liquid droplets. Ice frozen homogeneously using pure water or solutions produce growth rates that are elevated above those of solid spheres, with frozen solution drops producing the largest ice crystal growth rates. In contrast, solution droplets frozen heterogeneously using biological nuclei produce ice crystal growth rates that are nearly the same as solid ice spheres. Solution droplets frozen with immersed kaolinite minerals produce ice growth rates between those of solid ice spheres and ice formed from homogeneously-frozen solutions. Parcel model simulations using our immersion freezing and ice crystal growth data reveal that broad ice spectra can be produced through the action of heterogeneously frozen solution droplets alone.

https://illinois.zoom.us/j/87247933909?pwd=Yg9a5afZrUDAodWJBhap3HvxzMVVeo.1

Meeting ID: 872 4793 3909     Pass Code: 202496