Study of Cloud Condensation Nuclei Activities and Hygroscopic Properties Based on Core-Shell Model

Abstract

Cloud condensation nuclei (CCN) activities and hygroscopic properties of aerosol particles were studied based on the core-shell model with extended Köhler equation. Three kinds of core-shell particles were mainly considered: (1) insoluble core and soluble inorganic shell; (2) insoluble core and organic shell with limited solubility; (3) organic core with limited solubility and soluble inorganic shell. Results of the model calculations showed that Köhler curves of aerosol particles were different from classical Köhler curves of inorganic particles. Particle size, chemical composition and mass fraction of components all influence the curve shape, and the curve might show one or more extreme points of supersaturation. Critical supersaturation decreased when the mass fraction of the shell increased. This implied that the heterogeneous chemical reaction that happened to suspended particles in air could increase shell mass fraction and make particles more CCN active and hygroscopic. When the three models were compared, particles in model 3 were most CCN active, while those in model 2 were least CCN active. If the shell mass fraction was 0.1–0.2 for model 3 and 0.3–0.4 for model 1, the calculated hygroscopic parameter κ was closer to historical measuring results of 0.2–0.3 in polluted areas in China while the hygroscopic parameter would never be close to measuring results in model 2 no matter how high the shell mass fraction was. Based on discussion of two component particles of the core-shell model, more components in core-shell model could be considered, and the calculations were discussed in this article.