Modelling the role of organic aerosols in atmospheric CCN production

Abstract

Two source categories for cloud condensation nuclei (CCN) present in the atm. can be distinguished: direct emissions from various natural and anthropogenic sources (primary CCN) and atm. prodn. (secondary CCN). The latter source type, although extremely important on a global scale, has remained poorly quantified. During this project, a box model capable of simulating the main processes assocd. with atm. CCN prodn. has been developed. The model was applied to the investigation of the relative roles of sulfate and org. vapors in producing new CCN. Depending on meteorol. conditions and the availability of SO2 and org. precursors, the relative importance of these two compd. classes was shown to vary strongly. What it comes to org. vapors, the most important compd. properties appear to be their volatility (non-volatile org. vapors are needed to grow very small particles to larger sizes), their water soly. (sol. material assists the particle activation process during the cloud formation), and probably also their surface activity (surface-active compds. reduce the particle surface tension, thereby assisting the cloud droplet formation). When performing field expts., the relative importance of sulfate and different org. compds. in producing new CCN could be identified best by detg. the chem. compn. of particles smaller than 100 nm in diam. In smog-chamber expts. involving the oxidn. of org. vapors, more attention should be placed on the identification of nonvolatile reaction products and on their overall yields in these oxidn. reactions. [on SciFinder (R)]