Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 1 2007 10.5194/acpd-7-383-2007 http://www.atmos-chem-phys-discuss.net/7/383/2007/ http://www.atmos-chem-phys-discuss.net/7/383/2007/acpd-7-383-2007.html http://www.atmos-chem-phys-discuss.net/7/383/2007/acpd-7-383-2007.pdf 383 403 2007-01-10 Ice nucleation of ammonia gas exposed montmorillonite mineral dust particles A. Salam asalam@mathstat.dal.ca U. Lohmann G. Lesins Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada Department of Chemistry, University of Dhaka, Dhaka – 1000, Bangladesh Institute of Atmospheric and Climate Science, ETH Zurich, Switzerland The ice nucleation characteristics of montmorillonite mineral dust aerosols with and without exposure to ammonia gas were measured at different atmospheric temperatures and relative humidities with a continuous flow diffusion chamber. The montmorillonite particles were exposed to pure (100%) and diluted ammonia gas (25 ppm) at room temperature in a stainless steel chamber. There was no significant change in the mineral dust particle size distribution due to the ammonia gas exposure. 100% pure ammonia gas exposure enhanced the ice nucleating fraction of montmorillonite mineral dust particles 3 to 8 times at 90% relative humidity with respect to water (RHw) and 5 to 8 times at 100% RHw for 120 min exposure time within our experimental conditions. The percentages of active ice nuclei were 2 to 9 times higher at 90% RHw and 2 to 13 times higher at 100% RHw in 25 ppm ammonia exposed montmorillonite compared to unexposed montmorillonite. All montmorillonite particles are more efficient as ice nuclei with increasing relative humidities and decreasing temperatures. 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