Aerosol dynamics simulations on the connection of sulphuric acid and new particle formation
1Univ. of Helsinki, Dept. of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland
2Finnish Meteorological Institute, Climate and Global Change, P.O. Box 503, FI-00101 Helsinki, Finland
3University of Kuopio, Department of Physics, P.O. Box 1627, FI-70211 Kuopio, Finland
4Finnish Meteorological Institute, Kuopio Unit, P.O. Box 1627, FI-70211 Kuopio, Finland
Abstract. We have performed a series of simulations with an aerosol dynamics box model to study the connection between new particle formation and sulphuric acid concentration. For nucleation either activation mechanism with a linear dependence on the sulphuric acid concentration or ternary H2O-H2SO4-NH3 nucleation was assumed. We investigated the factors that affect the sulphuric acid dependence during the early stages of particle growth, and tried to find conditions which would yield the linear dependence between the particle number concentration at 3–6 nm and sulphuric acid, as observed in field experiments. The simulations showed that the correlation with sulphuric acid may change during the growth from nucleation size to 3–6 nm size range, the main reason being the size dependent growth rate between 1 and 3 nm. In addition, the assumed size for the nucleated clusters had a crucial impact on the sulphuric acid dependence at 3 nm. The simulations yielded a linear dependence between the particle number concentration at 3 nm and sulphuric acid, when a low saturation vapour pressure for the condensable organic vapour was assumed, or when nucleation took place at ~2 nm instead of ~1 nm. Comparison of results with activation and ternary nucleation showed that ternary nucleation cannot explain the experimentally observed linear or square dependence on sulphuric acid.