Atmospheric Aerosols: Formation and Growth

It is widely recognised that the increasing atmospheric concentrations of greenhouse gases such as carbon dioxide and methane can potentially drive a significant warming process of the earth’s climate. However, a topic of more recent attention is the possibility that increased atmospheric concentrations of aerosol particles might drive a significant radiative forcing process of the planet (see, for example, Charlson et al., 1992; and Charlson and Wigley, 1994). The increased aerosol concentrations are largely due to secondary particle production i.e. homogeneous nucleation from vapour precursors. The secondary aerosols have both natural and anthropogenic origin. Aerosol particles influence the climate by two distinct mechanisms: the direct reflection of solar radiation by aerosol particles, and the indirect increase in cloud reflectivity caused by enhanced number of cloud condensation nuclei. IPCC (1996) has reported that uncertainties in the estimation of direct and indirect aerosol effects on global climate are big (see Fig. 1.). These uncertainties arise largely from the limited information on the spatial and temporal distribution of aerosols and clouds. However, recently some progress has been made in evaluating the radiative effects of various aerosol components such as sulfate, organics, black carbon, sea-salt, and crustal species (Chuang et al., 1997; Haywood and Ramaswamy, 1998; Kaufman and Fraser, 1997; Winter and Chylek, 1997; Sokolik and Toon, 1996).