A single parameter representation of hygroscopic growth and cloud condensation nucleus activity

TLDR: In this paper, a method to describe the relationship between particle dry diameter and cloud condensation activity using a single hygroscopicity parameter is presented. But this method is limited to single and multi-component particles with varying amounts of inorganic, organic and surface active compounds.

Abstract: We present a method to describe the relationship between particle dry diameter and cloud condensation nu- clei (CCN) activity using a single hygroscopicity parameter . Values of the hygroscopicity parameter are between 0.5 and 1.4 for highly-CCN-active salts such as sodium chlo- ride, between 0.01 and 0.5 for slightly to very hygroscopic organic species, and 0 for nonhygroscopic components. Ob- servations indicate that atmospheric particulate matter is typ- ically characterized by 0.1<< 0.9. If compositional data are available and if the hygroscopicity parameter of each com- ponent is known, a multicomponent hygroscopicity parame- ter can be computed by weighting component hygroscopic- ity parameters by their volume fractions in the mixture. In the absence of information on chemical composition, exper- imental data for complex, multicomponent particles can be fitted to obtain the hygroscopicity parameter. The hygroscop- icity parameter can thus also be used to conveniently model the CCN activity of atmospheric particles, including those containing insoluble components. We confirm the applica- bility of the hygroscopicity parameter and its mixing rule by applying it to published hygroscopic diameter growth fac- tor and CCN-activation data for single- and multi-component particles containing varying amounts of inorganic, organic and surface active compounds. We suggest that may be fit to CCN data assuming s/a=0.072 J m 2 and present a table of derived for this value and T=298.15 K. The predicted hygroscopicities for mixtures that contain the surfactant ful- vic acid agree within uncertainties with the measured values. It thus appears that this approach is adequate for predict- ing CCN activity of mixed particles containing surface ac- tive materials, but the generality of this assumption requires further verification.