Measurements and modelling of aerosol single-scattering albedo: Progress, problems and prospects

The net effect of atmospheric aerosols in the radiation balance is determined by both their scattering and absorption of solar radiation. The combined optical effect is expressed in the single scatter albedo, ω, of the particles. Currently available data on ω are insufficient for definitive use in climate models because most of them are not corrected for the method-dependent effect of the scattering portion of the aerosol on the measured absorption, most refer to the dry state of the aerosol, and the coverage of the globe is far from being complete. Standardisation and calibration of the measurements is needed. Modelling exercises using currently available data on co should clearly state that corrections are required. The purpose of this review is not to suggest a particular range of values for single scatter albedo. Rather, it is to illustrate that the uncertainties are currently imbedded in various data sets because of the lack of calibration, the possibility that many of the extant methods systematically overestimate light absorption coefficients, and the necessity of including the influence of humidity in models.