Stable sulfate clusters as a source of new atmospheric particles

Abstract

The importance of atmospheric aerosols to the global radiation balance, to cloud formation, and to alleged human health effects has motivated us to investigate the formation and growth of atmospheric aerosol particles. Formation of new atmospheric particles (diameter between 3 and 10 nm) has been observed in a wide variety of low and high altitude locations. These aerosol particles are a source of Aitken mode nuclei and, after growing, one of the major sources of atmospheric cloud condensation nuclei (CCN) thus affecting cloud formation and global radiation balance. While some studies show that the measured new particle formation rates could be explained by binary sulphuric acid - water nucleation, others, particularly those in the marine boundary layer, or over the continental sites, indicate that observed ambient nucleation rates exceed those predicted by the binary scheme. The observed ambient H2SO4 concentrations are much less than needed for binary nucleation but appropriate for ternary nucleation (water - sulphuric acid - ammonia). Using a ternary nucleation modeling scheme with aerosol dynamics, nucleation is predicted to be ubiquitous in the troposphere yielding a reservoir of thermodynamically stable 1–3 nm clusters (TSC). The most likely pathway for CCN formation thus involves growth of these clusters up to 30–100 nm sizes via condensation of condensable vapours