Abstract
The source of condensation nuclei (CN ) in the marine environment and their evolution into CCN (Cloud Condensation Nuclei) are the focus of this chapter. CN are formed through homogeneous nucleation of H2SO4, H2O, and possibly NH3 vapor. The surface area of existing aerosol in the marine boundary layer is thought to provide a sufficient condensation sink for H2SO4 vapor, and thus, inhibits the vapor pressure required for homogeneous nucleation from being reached. Some cases of new-particle-formation, however, are observed under conditions of very low existing aerosol surface area. The timescales for freshly formed CN (r<5 nm) to grow into CCN (r<50 nm) under typical marine boundary layer conditions are thought to exceed the lifetime of marine CCN. It is postulated that the free troposphere is the most likely location for CN and CCN formation, as the tropospheric environmental conditions promote both CN formation and their growth into CCN because of longer residence timescales. This chapter presents observations of CN formation and decay from Antarctica and at a coastal site on the North East Atlantic.