Aerosol Science: Technology and Applications

Chapter 7

Atmospheric Particle Nucleation

Mikko Sipilä, Katrianne Lehtipalo and Markku Kulmala

Department of Physics, University of Helsinki, Finland

7.1 General Relevance

Atmospheric aerosol particles impact the earth's radiation budget directly by scattering and absorbing solar radiation. Aerosol particles also act as condensation nuclei for cloud droplet formation. Therefore, aerosol properties can indirectly influence the earth's radiation budget by affecting cloud albedo (Twomey, 1974), extent, precipitation, and lifetime (Rosenfeld, 2000; Ramanathan et al., 2001; Rosenfeld et al., 2008). The atmospheric aerosol system is impacted by anthropogenic activities, and the total deviation in the earth's radiative balance (radiative forcing) caused by human impact from the preindustrial climate to the year 2005 has been estimated to range between −0.4 and −2.7 W m⁻² (IPCC, 2007). The effect of changes in the aerosol system on radiative forcing is negative and therefore, at present, is partly counteracting the positive forcing of +2.64 W m⁻² (in 2005) (IPCC, 2007) originating mainly from greenhouse gas emissions. A significant fraction of the total aerosol effect results from the cloud albedo effect – currently estimated to be between −0.3 and −1.8 W m⁻² (in 2005) (IPCC, 2007) – forming the largest single source of uncertainty in our understanding of climate change. On the other hand, our level of understanding of many other effects, including the cloud lifetime effect, is so poor ...