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An evaluation of the performance and accuracy of a Cavity Attenuated Phase-Shift Single Scattering Albedo Monitor (CAPS PMssa, Aerodyne Res. Inc.) was conducted in an optical closure study with proven technologies: Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PMex, Aerodyne Res. Inc.); 3-wavelengh Integrating Nephelometer (TSI Model 3563); and 3-wavelength filter-based Particle Soot Absorption Photometer (PSAP, Radiance Research). The evaluation was conducted by connecting the instruments to a controlled aerosol generation system and comparing the measured scattering, extinction, and absorption coefficients measured by the CAPS PMssa with the independent measurements. Three different particle types were used to generate aerosol samples with single-scattering albedos (SSA) ranging from 0.4 to 1.0 at 630 nm wavelength. The CAPS PMssa measurements compared well with the proven technologies. Extinction measurement comparisons exhibited a slope of the linear regression line for the full data set of 0.96 (-0.02/+0.06), an intercept near zero, and a regression coefficient R² > 0.99; whereas, scattering measurements had a slope of 1.01 (-0.07/+0.06), an intercept of less than +/-2 x 10-6 m-1 (Mm-1), and a coefficient R² ∼ 1.0. The derived CAPS PMssa absorption compared well to the PSAP measurements at low levels (< 70 Mm-1) for the small particle sizes and modest (0.4 to 0.6) SSA values tested, with a linear regression slope of 1.0, an intercept of -4 Mm-1, and a coefficient R² = 0.97. Comparisons at higher particle loadings were compromised by loading effects on the PSAP filters. For the SSA measurements, agreement was highest (regression slopes within 1% ) for SSA = 1.0 particles, though the difference between the measured values increased to 9 % for extinction coefficients lower than 55 Mm-1. SSA measurements for absorbing particles exhibited absolute differences up to 18 %, though it is not clear which measurement had the lowest accuracy. For a given particle type, the CAPS PMssa instrument exhibited the lowest scatter around the average. This study demonstrates that the CAPS PMssa is a robust and reliable instrument for the direct measurement of the scattering and extinction coefficients and thus SSA. This conclusion also holds as well for the indirect measurement of the absorption coefficient with the constraint that the accuracy of this particular measurement degrades as the SSA and particle size increases. [ABSTRACT FROM AUTHOR]