The Direct Radiative Impact of Anthropogenic Aerosols Over the Northern Mediterranean

Aerosols are an important component of the climate system, yet current estimates of their radiative impact are enclosed within wide error limits and remain one of the largest uncertainties in atmospheric science. Scientific understanding of aerosol impacts is hindered by the complex nature of aerosol microphysical and chemical properties and their highly inhomogeneous spatio-temporal distribution The Aerosol Direct Radiative Impact Experiment (ADRIEX) aims to quantify some of the uncertainties arising from aerosol composition in atmospheric forcing via airborne and remotely-sensed measurements. Sampling took place during summer 2004 over the Po Valley (Italy), within the outflow across the Adriatic Sea, and over the Black Sea. The summertime Mediterranean provides an ideal situation for aerosol research; it has been highlighted in earlier studies as one of the most polluted regions in the world in terms of aerosol loading, and high insolation ensures large aerosol signals. This region is also noted for the wide directional range of air masses entering the basin, bringing a variety of aerosol species which become trapped by meteorological and orographical barriers. Infrequent precipitation leads to minimal opportunity for wet deposition of particles and, consequently, accumulation of pollutants. We present preliminary results from a comparison of the characteristics and radiative impact of aerosol detected over the western Black Sea and northern Adriatic Sea during flights on 3 and 5 September 2004, respectively. Trajectory analysis suggests these two sites are exposed to different sources. This is corroborated by the in-situ observations of aerosol microphysics and chemistry. Measurements of aerosol properties are used in a radiative transfer code to calculate the direct effect which is compared with changes in fluxes directly observed by onboard broadband radiometers. We also assess the importance of including more detailed aerosol chemistry in the estimates of the radiative impact.