We examined the impact of enhanced cloud nucleating aerosol concentrations on the microstructure of Arctic boundary layer clouds and on the downwelling radiative fluxes at the ice surface. This study extends a previous one to cloud-resolving simulations of the entire fall-winter-spring season during the 1997-1998 SHEBA field campaign. We used the Regional Atmospheric Modeling System at Colorado State University (RAMS@CSU) interfaced with the Los Alamos National Laboratory sea-ice model. This version of RAMS@CSU also includes sophisticated microphysical modules that considers the explicit nucleation of cloud droplets and a bi-modal representation of their spectrum. Sensitivity experiments were based on observed aerosol profiles and the 2-3 daily SHEBA soundings were utilized to provide time-evolving boundary conditions to the model. Probability density functions (PDFs) of various microphysical variables were generated for the entire 9-month period in order to establish comparisons between numerical experiments as well as between some simulated and observed radiative fluxes. Results indicate that aerosol entrainment from above the boundary layer strongly affects ice particle size distributions, and significantly increases the asymmetry of the surface fluxes PDFs. In summary, results suggest that intrusions of polluted air into the Arctic basin can reduce sea-ice thickness as it increases the net radiative forcing (except when liquid-phase clouds prevail).