ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-11-11131-2011 Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles Niedermeier D. 1 Hartmann S. 1 Clauss T. 1 Wex H. 1 Kiselev A. 1 2 Sullivan R. C. 3 DeMott P. J. 3 Petters M. D. 3 4 Reitz P. 5 6 Schneider J. 5 Mikhailov E. 7 Sierau B. 8 Stetzer O. 8 Reimann B. 9 Bundke U. 9 Shaw R. A. 10 Buchholz A. 11 Mentel T. F. 11 Stratmann F. 1 Leibniz Institute for Tropospheric Research, Leipzig, Germany Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Eggenstein-Leopoldshafen, Germany Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA Particle Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany Institute for Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany Fock Institute of Physics, St. Petersburg State University, St. Petersburg, Russia Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland Institute for Atmospheric and Environmental Sciences, Goethe University, Frankfurt, Germany Department of Physics, Michigan Technological University, Houghton, Michigan, USA IEK 8: Troposphere, Research Center Jülich, Jülich, Germany 09 11 2011 11 21 11131 11144 Copyright: © 2011 D. Niedermeier et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/11/11131/2011/acp-11-11131-2011.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/11/11131/2011/acp-11-11131-2011.pdf

During the measurement campaign FROST 2 (FReezing Of duST 2), the Leipzig Aerosol Cloud Interaction Simulator (LACIS) was used to investigate the influence of various surface modifications on the ice nucleating ability of Arizona Test Dust (ATD) particles in the immersion freezing mode. The dust particles were exposed to sulfuric acid vapor, to water vapor with and without the addition of ammonia gas, and heat using a thermodenuder operating at 250 °C. Size selected, quasi monodisperse particles with a mobility diameter of 300 nm were fed into LACIS and droplets grew on these particles such that each droplet contained a single particle. Temperature dependent frozen fractions of these droplets were determined in a temperature range between −40 °C ≤<i>T</i>≤&minus;28 °C. The pure ATD particles nucleated ice over a broad temperature range with their freezing behavior being separated into two freezing branches characterized through different slopes in the frozen fraction vs. temperature curves. Coating the ATD particles with sulfuric acid resulted in the particles' IN potential significantly decreasing in the first freezing branch (<i>T</i>>−35 °C) and a slight increase in the second branch (<i>T</i>≤−35 °C). The addition of water vapor after the sulfuric acid coating caused the disappearance of the first freezing branch and a strong reduction of the IN ability in the second freezing branch. The presence of ammonia gas during water vapor exposure had a negligible effect on the particles' IN ability compared to the effect of water vapor. Heating in the thermodenuder led to a decreased IN ability of the sulfuric acid coated particles for both branches but the additional heat did not or only slightly change the IN ability of the pure ATD and the water vapor exposed sulfuric acid coated particles. In other words, the combination of both sulfuric acid and water vapor being present is a main cause for the ice active surface features of the ATD particles being destroyed. A possible explanation could be the chemical transformation of ice active metal silicates to metal sulfates. The strongly enhanced reaction between sulfuric acid and dust in the presence of water vapor and the resulting significant reductions in IN potential are of importance for atmospheric ice cloud formation. Our findings suggest that the IN concentration can decrease by up to one order of magnitude for the conditions investigated.

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