American Association for Aerosol Research - Abstract Submission

AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA

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Heterogeneous Ice Nucleation and Water Uptake by Field-Collected Atmospheric Particles Below 273 K

BINGBING WANG, Alexander Laskin, Tobias Roedel, Mary Gilles, Ryan Moffet, Alexei Tivanski, Daniel Knopf, Pacific Northwest National Laboratory

     Abstract Number: 615
     Working Group: Aerosols, Clouds, and Climate

Abstract
Ice nucleation initiated by aerosol particles through heterogeneous nucleation is not well understood. Onset conditions of water uptake and heterogeneous ice nucleation by particles collected in Los Angeles and Mexico City were determined as a function of temperature (200-273 K) and relative humidity with respect to ice (RH$_(ice)). Single particle characterization was provided by micro-spectroscopic analyses using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Four dominant particle types were identified including soot associated with organics, soot with organic and inorganics, inorganic particles of marine origin coated with organic material, and Pb/Zn-containing particles apportioned to emissions relevant to waste incineration. Above 230 K, significant differences in onsets of water uptake and immersion freezing of different particle types were observed. Below 230 K, particles exhibited high deposition ice nucleation efficiencies and nucleated ice at RH$_(ice) well below homogeneous ice nucleation limits. The data suggest that water uptake and immersion freezing are more sensitive to changes in particle chemical composition compared to deposition ice nucleation. The investigated anthropogenic and marine influenced particles, exhibiting various chemical and physical properties, showed distinctly different ice nucleation efficiencies and can serve as efficient IN at atmospheric conditions typical for cirrus and mixed-phase clouds.