Variability of Desert Dust Radiative Efficiency due to Contamination by Biomass Burning Aerosol

During the long-range transport, mineral dust can interact with anthropogenic aerosols and thus modify its radiative properties. This occurs in the Western Africa region, where aerosol mixture is produced as a result of coincidence of biomass burning aerosol outbreaks and frequent dust storms. In the framework of the African Monsoon Multidisciplinary Analysis, we measured optical properties and evaluated variability in radiative efficiency for several events of aerosol mixture observed over the AERONET site in M'Bour, Senegal. The radiative efficiency at the bottom of the atmosphere of aerosol mixture appeared to be stronger (up to two times) than the one of pure dust. However, at the top of the atmosphere the dust radiative efficiency remained dominant. We also evaluated the importance of accounting for dust particles nonsphericity in simulating radiative effects. Our test showed that neglecting nonsphericity of aerosol particle shape (for dust or aerosol mixture) can result in a pronounced bias of the daily average aerosol radiative effect, of up to 10% overestimation.