Ice Nucleation Studies of Mineral Dust Particles with a New Continuous Flow Diffusion Chamber

A new continuous flow diffusion chamber (CFDC) has been designed and constructed to study the ice nucleation efficiency of natural and anthropogenic aerosol particles over a range of temperatures and supersaturations. The CFDC system at Dalhousie University, Canada is based on the design of (Rogers et al. 1988, 1994) at Colorado State University, USA. A steady airflow (2.83 lpm) composed of sheath flows and an aerosol flow passes through the annular gap of the diffusion chamber. The walls of the chamber are ice-covered and are held at different temperatures. Aerosol particles are injected into the center of the gap near the location of maximum supersaturation. Particles greater than 5 μm in aerodynamic diameter are removed with impactors before entry to the chamber. Ice crystals are identified with an optical particle counter at the outlet of the chamber. In this article we report on the ice nucleation results of two mineral dust particles of potential atmospheric relevance, kaolinite and montmorillonite. Our results indicate that kaolinite and montmorillonite act as efficient ice nuclei in deposition/condensation nucleation mode. The onset relative humidity of both kaolinite and montmorillonite mineral dust particles were determined. The percentage of active ice nuclei is higher in montmorillonite compared to kaolinite at each temperature within the experimental conditions. The fraction of active ice nuclei increases with decreasing temperature and also with increasing relative humidity.

Acknowledgments

We are grateful for support from the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS) and the National Science and Engineering Research Council (NSERC) of Canada. The authors acknowledge the suggestions from two anonymous reviewers, as well as Richard Leaitch and Ravi Raghunathan for their comments and suggestions.