Comparison of Two Filter-Based Reflectance Methods to Measure the Light Absorption by Atmospheric Aerosols

Abstract

wo reflectance techniques, based on Kubelka?Munk (K-M) theory and on the Beer?Lambert (B-L) law, were used to measure the absorption coefficient of aerosol particles collected on a filter. The two methods agreed, with the B-L technique being higher than the K-M method by a factor of 1.10, but with a correlation, r2, between the two methods of 0.99. The aerosol absorption Ångström exponents (AAE) between the two methods also agreed within 0.4 and were in the range of measurements reported in the literature with other techniques. The precision of the two methods depends on the volume of air sampled, but a typical sampling scheme (100 L min?1, 10 cm2 sampling area, full day of sampling) results in a precision in the measurement of the aerosol light absorption coefficient of 0.05 Mm?1.