Data of Interest

To characterize aerosols properly requires information on particle amount, size, composition, as well as shape in space and time. The relevant optical properties are AOD, ro0, and g. These properties are associated with overall extinction, the probability for scattering (as opposed to absorption), and the scattering behavior. AOD is the vertically integrated attenuation of radiation caused by scattering and absorption by particles; ro0 is the single-scattering albedo and captures the scattering probability of attenuation event. The asymmetry factor, g, captures the angular probability of scattering by the cosine (of the scattering angle) weighted integral value. All three properties are a function of location, time, altitude, and (at least solar) wavelength. Because of limitations in aerosol measurements, the requirements for aerosols in global applications are usually relaxed to maps of mid-visible properties of vertically integrated aerosols, and often only to that of the AOD. The justification here is that (a) aerosol amount (captured by AOD) is more variable than size or composition, (b) aerosols are located predominantly in the lower troposphere, and (c) mid-visible aerosol properties are most important, because in that solar spectral region, the product of particle cross section and available (solar) energy is at a maximum. Still, there is a need to account for non-negligible variations in particle size and composition. This requires additional maps of the mid-visible column properties for ro0 and g. The necessary data for g can be substituted by using a parameter that is easier to measure: mid-visible AnP, which is defined by the AOD spectral dependence as the negative slope in log/log space. This substitution is possible, as both properties are sensitive to particle size. Thus, monthly global maps for AOD, ro0, and AnP are the minimum that are needed.

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