Measurements of Cloud Condensation Nuclei Activity and Hygroscopicity of Fresh Unprocessed Regional Dust Samples and Clays

PRASHANT KUMAR (1), Irina N. Sokolik (2), Athanasios Nenes (1, 2)

(1) School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA (2) School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA

     Abstract Number: 448
     Last modified: May 12, 2010

Abstract
Mineral dust aerosols represent a dominant source of particulate mass in the atmosphere and have been found to play an important role in warm clouds due to their ability to serve as efficient Cloud Condensation Nuclei (CCN). The ability of dust particles to serve as CCN under atmospherically relevant supersaturations depends on their mineralogy, size, morphology, and atmospheric processing. In this work, we investigate the CCN activation characteristics of mineral dust samples from Northern America, African soils, and East Asian soils, as well as individual clays and minerals using a Continuous-Flow Streamwise Thermal Gradient CCN Counter (CCNc). Based on the experimental exponent, xexp, derived from the dependence of critical supersaturation, sc, with particle dry diameter, Ddry, we determine the dominant physics of activation (i.e., adsorption activation theory (AT) or traditional Köhler theory (KT)) for dust particles from different global regions. The CCN activity of the regional dust samples is parameterized in terms of the mineralogical composition, based on the CCN activation of various individual minerals (clays and carbonates) and the derived experimental exponents from the sc-Ddry relationship. Based on the method of threshold droplet growth analysis, this work reports, for the first time, the activation kinetics of dust CCN and parameterized water vapor uptake coefficients. Finally, the hygroscopicity of dust aerosol is constrained by relating CCN activation of “wet” generated mineral aerosol to the presence of soluble salts on the mineral dust surface.