A model prediction of the yield of cloud condensation nuclei from coastal nucleation events

The formation and evolution of new particles during coastal nucleation events are examined using the aerosol dynamic and gas-phase chemistry model AEROFOR2. Coastal regions are known to be a strong source of natural aerosol particles and are also strong sources of biogenic vapors which can condense onto aerosol particles, thus resulting in particle growth. A number of model simulations were performed to determine the instantaneous nucleation rate along with the source rate of a generic biogenic vapor leading to the observed particle size distributions which indicate the rapid appearance of ∼10 ⁵-10⁶ cm^-3 nucleation mode particles in this environment. Model calculations suggest values of 3 × 10⁵ cm^-3 s^-1 to 3 × 10⁶ cm^-3 s^-1 for the instantaneous nucleation rate and a value of 5 × 10⁷ cm^-3 s^-1 for the condensable vapor source rate in order to reproduce the observed concentrations. A significant fraction of these new particles survive to grow into cloud condensation nuclei (CCN) sizes for supersaturations typically encountered in boundary layer clouds during subsequent evolution over 3 days under clear-sky conditions, thus contributing to the indirect radiative effect of aerosols. The amount of CCN is mainly affected by coagulation between particles and condensation of the biogenic vapor and, to a lesser extent, by condensation of sulphuric acid formed by DMS oxidation. In all simulated cases, an increase of more than 100% in CCN concentration, for supersaturations >0.35% was observed.