Aerosol Single-Scattering Albedo Determined by Horizontal Extinction Closure

Abstract

Single-scattering albedo describes the relative amount of scattering and absorption of light by aerosol particles and is one of the most important parameters for the evaluation of the effect of the atmospheric aerosol on climate. Despite this fact, there are very few data on this property and in most cases the existing data do not take into account the effects of relative humidity. Moreover, the absorption coefficient, which is used to calculate single-scattering albedo, usually lacks a method dependent calibration. We performed a closure study on the aerosol extinction coefficient by measuring extinction directly in the atmosphere and compared it with simultaneously measured scattering and absorption coefficients for five days in October and November 1999 in Kyoto, Japan. We found that relative humidity plays an important role in an accurate determination of the single-scattering albedo. An error analysis showed an increase of uncertainty for decreasing values of the single-scattering albedo and the resulting error depended strongly on the method of calculation. Closure tests showed that extinction coefficients obtained from in-situ methods compared to ambient values are mostly within error bars.