Formation of sulphuric acid aerosols and cloud condensation nuclei: An expression for significant nucleation and model comparison

A new analytical expression has been derived to predict atmospheric conditi ons where homogeneous water-sulphuric acid nucleation will have a significa nt effect on aerosol and cloud condensation nuclei population. In the expre ssion, the condensational sink due to pre-existing aerosol particles and so urce due to chemical production of sulphuric acid have been taken into acco unt. The analytical expression has been derived using a sectional aerosol d ynamic model including nucleation, condensation, coagulation, deposition an d sulphuric acid formation in the gas phase. In the present study we have a lso compared the sectional model with modal and monodisperse models. All mo dels may be used for predicting the onset of significant new particle forma tion. However, the computationally more efficient models-monodisperse, moda l and sectional with low number of sections-over- or underpredict particle formation in some situations. (C) 1999 Elsevier Science Ltd. All rights res erved.