Effect of ammonium bisulphate formation on atmospheric water-sulphuric acid-ammonia nucleation

The effect of formation of stable ammonium bisulphate clusters on the ternary water-sulphuric acid-ammonia nucleation was investigated by means of the classical thermodynamics. The performed calculations show that most of the sulphuric acid in the atmosphere is likely to be bound to stable ammonium bisulphate clusters. Consequently the nucleation rates calculated with the new model are orders, sometimes even tens of orders, of magnitude lower than the rates produced by the previous ternary model which neglected the formation of these clusters. The new nucleation rates compare favourably with the available experimental results, unlike the old ones, which are far too high. In contrast to the old ternary model, the revised model does not predict significant nucleation rates that would explain new particle formation events every time they are observed, and we have to look for other nucleation mechanisms like multi-component nucleation involving organics or ion induced nucleation to understand atmospheric new particle formation.