Abstract: Present work aims to determine the relationship between Kelvin radii and Bulk hygroscopicity factor, the effects of these factors on Kelvin effect and Water activity of atmospheric aerosol and investigate how both Kelvin effect and Water activities affect atmospheric processes based on (MVN mix ratios). In the present study, microphysical properties of aerosols were extracted from the Optical Properties of Aerosols and Clouds (OPAC) at seven relative humidity (50%, 70%, 80%, 90%, 95%, 98% and 99%) for ten aerosol models (Arctic, Antarctic, Continental clean, continental polluted, continental average, Desert, Maritime clean, maritime polluted, maritime tropical and Urban,).