Aerosol seasonal variability over the Mediterranean region and relative impact of maritime, continental and Saharan dust particles over the basin from MODIS data in the year 2001

[摘要] The one-year (2001) record of aerosol data from the space borne ModerateResolution Imaging Spectroradiometer (MODIS) is analyzed focusing on theMediterranean region. The MODIS aerosol optical thickness standard product(AOT at 550nm) provided over both land and ocean is employed to evaluatethe seasonal and spatial variability of the atmospheric particulate over theregion. Expected accuracy of the MODIS AOT is (±0.05±0.2xAOT)over land and (±0.03±0.05xAOT) over ocean. Theseasonal analysis reveals a significant AOT variability all over the region,with minimum values in Winter (AOT<0.15) and maximum in Summer (AOT>0.2).The spatial variability is also found to be considerable, particularlyover land. The impact of some major urban sites and industrialized areas isdetectable. For the sole Mediterranean basin, a method (aerosol mask) wasimplemented to separate the contribution of maritime, continental and desertdust aerosol to the total AOT. Input of both continental and desert dustparticles is well captured, showing North-to-South and South-to-North AOTgradients, respectively. A quantitative summary of the AOT seasonal andregional variability is given for different sectors of the Mediterraneanbasin. Results of this summary were also used to test the aerosol maskassumptions and indicate the method adopted to be suitable for the aerosoltype selection. Estimates of the atmospheric aerosol mass load wereperformed employing specifically-derived mass-to-extinction efficiencies(α). For each aerosol type, a reliable mean α value wasdetermined on the basis of both lidar measurements of extinction and aerosolmodels. These estimates indicate a total of 43Mtons of desert dustsuspended over the basin during 2001. A comparable value is derived formaritime aerosol. Opposite to the dust case, a minor seasonal variability(within 15%) of maritime aerosol mass is found. This latter result isconsidered a further check of the suitability of the methodology adopted toseparate, on the basis of MODIS data, the three aerosol types which dominatethe Mediterranean region.

[学科分类] 大气科学