Researchers elucidate nucleation mechanism for aerosols

On local to global scales, newly formed particles influence climate by affecting the atmospheric radiation balance, both directly through scattering and absorbing incoming solar radiation, and indirectly through impacts on cloud properties and lifetimes. They contribute to poor air quality associated with urban pollution and are known to have negative impacts on health.

Using field measurement and chamber data, an interdisciplinary team of researchers led by Professor Peter McMurry from the Department of Mechanical Engineering, and involving chemistry graduate student Mari Titcombe and Chemistry Professor Ilja Siepmann, developed a reaction-based model describing particle formation from sulfuric acid + amines/ammonia. This model is based on a specific sequence of acid-base reactions (see graphic), using empirical estimates of sulfuric acid cluster evaporation rates obtained from new measurements of neutral molecular clusters, and enables the accurate prediction for particle formation rates needed for large-scale atmospheric simulations. The findings of this research are reported in the Proceedings of the National Academy of Sciences (PNAS), USA 109, 18713-18718 (2012).