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Ground-based logistics / results on Djougou (Bénin)

Ground-based logistics / results on Djougou (Bénin). Objectives : obtain measurements of physical, chemical and radiative properties of mixed aerosol (dust & biomass burning) during the dry season in WA study the modification of the radiative budget by aerosols at local scale.

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Ground-based logistics / results on Djougou (Bénin)

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  1. Ground-based logistics / results on Djougou (Bénin) Objectives : • obtain measurements of physical, chemical and radiative properties of mixed aerosol (dust & biomass burning) during the dry season in WA • study the modification of the radiative budget by aerosols at local scale

  2. What do we measure during SOP_0 / aerosol microphysical properties • aerosol number size distribution (0.05 – 0.5 µm) from SMPS • aerosol number size distribution (0.5 – 10 µm) from GRIMM • particle number concentration aerosol radiative properties from Mie theory (number size distribution and refractive index from chemical composition) derived properties optical closure with ground-based radiative measurements • aerosol mass size distribution for major ions, BC and • OC from impactor Dekati (13 stages)

  3. What do we measure during SOP_0 / aerosol radiative properties • light absorption coefficient (σap) from MAGEE aethalometer (at 7) • at the surface derived properties aerosol single scattering albedo (at 520nm) at the surface • light scattering coefficient (σsp) from ECOTECH nephelometer • (at 520nm) at the surface PHOTON / LOA • aerosol optical depth (440, 670, 870 and 1020nm) • aerosol volume size distribution (0.05 < r < 10 µm) for total atmospheric • column (Dubovik et al., 2002) • aerosol single scattering albedo and asymmetry parameter (at 4 ) for • the total atmospheric column (Dubovik et al., 2002) derived properties vertical profiles of aerosol extinction coefficient & angström exponent (Coll. SA) • vertical profiles of aerosol backscattering coefficients (Coll. SA)

  4. Aerosol optical depth & aerosol size distribution of mixed aerosols on Djougou SOP_0 AOD_scattering AOD_absorption AOD • strong AOD during SOP_0 with AOD  0.9 at 440nm • extinction mostly due to scattering but also by absorption of solar radiations ( 5-20 %) Aerosol optical depth at 440nm • bimodal size distribution with a fine ( 0.1 µm) and a coarse mode ( 1-10µm) • mixing between dust (dominant) and BB  confirmation with chemical measurements • comparison with retrievals on Niamey ?? • comparison with ground-based measurements SOP_0 Radius (µm)

  5. Aerosol single scattering albedo of mixed aerosols on Djougou SOP_0 strong absorbing mixed aerosols for the total atmospheric column with SSA  0.84  0.04 at 440nm Aerosol single scattering albedo (440 nm) strong absorbing mixed aerosols at the surface with SSA  0.87 at 520nm some differences appear between SSA estimated at the surface and those inverted for the atmospheric column Lidar measurements nephelometer & aethalometer Aerosol single scattering albedo (520 nm) SOP_0

  6. Asymmetry factor of mixed aerosols on Djougou g is higher on Djougou  gSOP_O  0.68 compared to other campaigns, due to the presence of dust aerosols.

  7. Direct radiative forcing of mixed aerosols at local scale / first results • future works to improve the estimation of the local direct radiative effect : • use pyranometer measurements for comparison with downwards fluxes simulated • with radiative transfer model • use satellite sensor (MODIS) for comparison with upwards radiance simulated with • radiative transfer model • use Lidar measurements for estimating the vertical profiles of aerosol extinction • use RH, O3 and T° profiles estimated from balloons for upper atmosphere AOD SSA Wavelenght (nm) strong heating of the aerosol layer Direct radiative forcing (W.m-2) asymmetry factor strong cooling at the surface Wavelenght (nm)

  8. Vertical profiles used in radiative transfer modelling AOD  0.75 (550nm)

  9. Fluxes measurements Meteorological conditions NO emissions At ground level The other parameters… NOx-O3- CO

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