The relative contributions to the tropospheric burdens of CN and CCN from nucleation versus primary emissions are very uncertain. To evaluate these contributions, we perform global aerosol microphysical simulations to explore how uncertainties in nucleation mechanisms, nucleation rates, primary emissions amount, and primary emissions size distributions affect the CN and CCN concentrations. The global model used is the GISS II-prime general circulation model with the size-resolved aerosol microphysics module, TOMAS (1-2). Various binary, ternary and ion-induced nucleation theories are tested in the model to determine how they affect the spatial and temporal distribution of CN and CCN (3-5). For example, a robust feature of global aerosol microphysics models is that binary nucleation parameterizations predict high nucleation rates in the upper troposphere, but the impact of these particles on boundary layer CCN concentrations requires investigation. A pseudo steady-state approximation is applied to gas phase sulfuric acid allowing for longer time steps during the calculation of nucleation and condensation and a decrease the computation time. The sensitivity of CN and CCN concentrations to the fraction of sulfur emitted as “primary” sulfate particles and the emission size of biomass burning aerosol are explored. Also investigated is the effect of sub-grid scale coagulation on the concentration of CN and CCN.

(1) Hansen, J. et al., Mon. Weather Rev., 111, (1983). (2) Adams, P. J., and J. H. Seinfeld., J. Geophys. Res., 107, (2002). (3) Vehkamaki, H., et al., J. Geophys. Res., 107, (2002). (4) Napari, I., et al., J. Geophys. Res., 107, (2002). (5) Modgil, M. S., et al., J. Geophys. Res., 110, (2005).