Title Heterogeneous freezing of droplets with immersed mineral dust particles; measurements and parameterization
Author Niedermeier, D.; Hartmann, S.; Shaw, R.A.; Covert, D.; Mentel, T.F.; Schneider, J.; Poulain, L.; Reitz, P.; Spindler, C.; Clauss, T.; Kiselev, A.; Hallbauer, E.; Wex, H.; Mildenberger, K.; Stratmann, F.
Author Affil Niedermeier, D., Leibniz Institute for Tropospheric Research, Leipzig, Germany. Other: Michigan Technological University; University of Washington; Research Center Jülich, Germany; Max Planck Institute for Chemistry, Germany; Johannes Gutenberg-Universität Mainz, Germany
Source Atmospheric Chemistry and Physics, 10(8), p.3601-3614, . Publisher: Copernicus, Katlenburg-Lindau, International. ISSN: 1680- 7316
Publication Date 2010
Notes In English. Published in Atmospheric Chemistry and Physics Discussions: 24 July 2009, http://www.atmos-chem-phys- discuss.net/9/15827/2009/acpd-9-15827- 2009.html ; accessed in May, 2011. 44 refs. GeoRef Acc. No: 310057
Index Terms aerosols; atmospheric pressure; clouds (meteorology); crystals; dust; experimentation; freezing; ice; ice crystals; measurement; minerals; particles; sediments; temperature; ammonium sulfate; atmosphere; clastic sediments; clouds; coating; droplets; experimental studies; heterogeneity; inorganic acids; size; stochastic processes
Abstract During the measurement campaign FROST (FReezing Of duST), LACIS (Leipzig Aerosol Cloud Interaction Simulator) was used to investigate the immersion freezing behavior of size selected, coated and uncoated Arizona Test Dust (ATD) particles with a mobility diameter of 300 nm. Particles were coated with succinic acid (C4H6O4), sulfuric acid (H2SO4) and ammonium sulfate ((NH4)2SO4). Ice fractions at mixed-phase cloud temperatures ranging from 233.15 K to 239.15 K (±0.60 K) were determined for all types of particles. In this temperature range, pure ATD particles and those coated with C4H6O4 or small amounts of H2SO4 were found to be the most efficient ice nuclei (IN). ATD particles coated with (NH4)2SO4 were the most inefficient IN. Since the supercooled droplets were highly diluted before freezing occurred, a freezing point suppression due to the soluble material on the particles (and therefore in the droplets) cannot explain this observation. Therefore, it is reasonable to assume that the coatings lead to particle surface alterations which cause the differences in the IN abilities. Two different theoretical approaches based on the stochastic and the singular hypotheses were applied to clarify and parameterize the freezing behavior of the particles investigated. Both approaches describe the experimentally determined results, yielding parameters that can subsequently be used to compare our results to those from other studies. However, we cannot clarify at the current state which of the two approaches correctly describes the investigated immersion freezing process. But both approaches confirm the assumption that the coatings lead to particle surface modifications lowering the nucleation efficiency. The stochastic approach interprets the reduction in nucleation rate from coating as primarily due to an increase in the thermodynamic barrier for ice formation (i.e., changes in interfacial free energies). The singular approach interprets the reduction as resulting from a reduced surface density of active sites.
URL http://www.atmos-chem-phys.net/10/3601/2010/acp-10-3601-2010.pdf
Publication Type journal article
Record ID 65006795