An inter-comparison study of the aerosol optical thickness (AOT) at 0.55 μm retrieved using different satellite instruments and algorithms based on the analysis of backscattered solar light is presented for a single scene over central Europe on October 13th, 2005. For the first time comparisons have been performed for as many as six instruments on multiple satellite platforms. Ten different algorithms are briefly discussed and inter-compared. It was found that on the scale of a single pixel there can be large differences in AOT retrieved over land using different retrieval techniques and instruments. However, these differences are not as pronounced for the average AOT over land. For instance, the average AOT at 0.55 μm for the area 7-12E, 49-53N was equal to 0.14 for MISR, NASA MODIS and POLDER algorithms. It is smaller by 0.01 for the ESA MERIS aerosol product and larger by 0.04 for the MERIS BAER algorithm. AOT as derived using AATSR gives on average larger values as compared to all other instruments, while SCIAMACHY retrievals underestimate the aerosol loading. These discrepancies are explained by uncertainties in a priori assumptions used in the different algorithms and differences in the sensor characteristics. Validation against AERONET shows that MERIS provides the most accurate AOT retrievals for this scene.

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[1] Wavelength-dependent optical properties together with the size-resolved elemental and chemical composition of the atmospheric aerosol were measured at Yasaka, Japan, near Wakasa Bay on the coast of the Sea of Japan. Observations were performed as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) campaign during three weeks in March and April 2001. Information about the detailed chemical composition and the size distribution of the aerosol, including absorbing material, was used to model optical properties of the aerosol and compare them with directly measured properties. Continuous, size-resolved measurements of aerosol scattering and backscattering coefficients were made at wavelengths of 450, 550, and 700 nm. Aerosol size distribution measurements were taken three times during the campaign for a period of 3-4 days each, using cascade impactors. One of the measurement periods was influenced by an intense yellow dust event originating on the Asian continent (20-25 March 2001), while the other two data sets were only weakly influenced by dust particles. The size-resolved measurement of aerosol scattering coefficients and the chemical analysis showed that the dust was accompanied by fine accumulation-mode particles during the dust event. The effects of the mineral dust particles on the optical and chemical properties of the aerosol are discussed, and data sets with and without desert dust influence are compared. Before the optical closure calculation a mass closure of the aerosol was performed, and the influence of the nonanalyzed fraction on the calculated optical properties of the aerosol is investigated. In general, good agreement between measured and modeled aerosol optical properties was found for the aerosol scattering and absorption coefficients, while less agreement was found for the backscattering coefficients, especially for the coarse mode of the aerosol. A distinct difference between the dust and nondust periods was found for the wavelength-dependent single-scattering albedo.

Boreal forest fires are one of the major emission sources of trace atmospheric constituents in mid and high latitudes in the Northern Hemisphere. From late May through early June 2003, dense smoke aerosols that originated from large forest fires in Siberia were monitored on the summit of Mt. Fuji (3776 m msl.), Japan, a free‐tropospheric height monitoring site where measurements of atmospheric chemistry were briefly intensified during a research project called Atmospheric Environmental Impact of Aerosols in East Asia (AIE). Inside a smoke layer, concentrations of black carbon (BC) measured by an Aethalometer exceeded 1900 ng m−3 with a concurrent increase of carbon monoxide mixing ratio. The slope of a BC/CO regression line was steeper than those obtained in other studies using measurements from lower‐altitude ground monitoring stations, suggesting minimal wet removal processes. The smoke aerosols contained high levels of n‐alkanes of high molecular weight and indicated high carbon preference indices. The time series of CO and O3 mixing ratios indicated a double‐layered vertical structure in which a high O3 mixing ratio layer lay on top of a smoke layer. The wavelength dependence of the absorption coefficient of the smoke showed a slope much steeper than that measured in urban influenced measurements. The higher absorption in the shorter wavelengths was consistent with an abundance of organic species within the smoke.