Importance of adsorption for CCN activity and hygroscopic properties of mineral dust aerosol

This study uses published data on dust-water interactions to examine the importance of including water adsorption effects when describing the hygroscopic and cloud condensation nuclei (CCN) behavior of mineral dust aerosol. Adsorption activation theory (AT) better represents fresh dust-water interactions than Köhler theory (KT), as i) a consistent set of adsorption parameters can describe the hygroscopic behavior of dust (under both sub and supersaturated conditions), and ii) the dependence of critical supersaturation, sc, with particle dry diameter, Ddry, is closer to observations. The long adsorption timescale could also contribute to the large differences observed between dry and wet generated dust hygroscopicity. If KT and AT are consistently applied to the same dust size distribution, KT predicts up to tenfold higher CCN and 40% higher droplet number concentration than AT. This profoundly different behavior between the theories suggests that both may be required for a comprehensive description of atmospheric dust CCN activity. Copyright 2009 by the American Geophysical Union.