The contribution of anthropogenic aerosols to aerosol light-scattering and CCN activity in the California coastal zone

Aircraft-based measurements of aerosol light-scattering coefficient, cloud condensation nuclei (CCN) measured directly or by proxy, and aerosol chemical composition are reported for three different years in the region of the large stratocumulus deck off the California coast. Receptor modeling is used to differentiate the contributions of the main aerosol sources to the light scattering and CCN activity. The contribution of anthropogenic sources to the two climatically important aerosol parameters (for direct and indirect forcing) varied from year to year but, on average, was found to be 67% in the case of CCN concentration and 57% in the case of light-scattering coefficient.