A sectional method for representing the atmospheric aerosol size distribution is evaluated for calculating the optical properties used in atmospheric radiative transfer calculations. Many current atmospheric aerosol models and measurement analysis methods are based on a lognormal representation of the aerosol size distribution. The sectional method offers the advantage over the lognormal size distribution that as the aerosol size distribution evolves with time, for example, as in the case of the Mount Pinatubo stratospheric aerosol, regional haze aerosol, or stack plume particles, the optical properties are computed only once for each size section and do not need to be recomputed as the aerosol size distribution changes. Thus the computational costs are considerably reduced. The sectional approach was evaluated by comparing the aerosol optical properties calculated with a continuous distribution to those calculated with a sectional distribution. The sectional approach was shown to be most accurate when the optical properties were integrated assuming a constant surface area distribution within each section. For a sectional size distribution with nine sections between 0.01 and 10 μm in diameter, the results show a maximum error of 6% for the scattering coefficient, 10% for the phase function, and 4% in the sky radiance. The results indicate that the sectional approach offers an excellent compromise between accuracy and computational efficiency. ¿ American Geophysical Union 1996