Modelling of strong heterogeneities in aerosol single scattering albedos over a polluted region.

To date, most models dedicated to the investigation of aerosol direct or semi‐direct radiative forcings have assumed the various aerosol components to be either completely externally mixed or homogeneously internally mixed. Some recent works have shown that a core‐shell treatment of particles should be more realistic, leading to significant differences in the radiative impact as compared to only externally or well‐internally mixed states. To account for these studies, an optical module, ORISAM‐RAD, has been developed for computing aerosol radiative properties under the hypothesis of internally mixed particles with a n‐layer spherical concentric structure. Mesoscale simulations using ORISAM‐RAD, coupled with the 3D mesoscale model Meso‐NH‐C, have been performed for one selected day (06/24/2001) during the ESCOMPTE experiment in the Marseilles‐Fos/Berre region, which illustrate the ability of this new module to reproduce spatial heterogeneities of measured single scattering albedo (ωo), due to industrial and/or urban pollution plumes