An evaluation of the Cavity Attenuated Phase Shift particle light extinction monitor (CAPS PM<sub>ex</sub>) using a combination of a 3-wavelength Integrating Nephelometer (NEPH) and a 3-wavelength filter-based Particle Soot Absorption Photometer (PSAP) was carried out using both laboratory-generated test particles and ambient aerosols. An accurate determination of a fixed pathlength correction for the CAPS PM<sub>ex</sub> was made by comparing extinction measurements using monodisperse PSL spheres in combination with Mie scattering calculations to account for the presence of PSL conglomerates. These studies yielded a linear instrument response over the investigated dynamical range from 20 to 450 Mm<sup>−1</sup> (10<sup>−6</sup> m<sup>−1</sup>) with a linear correlation coefficient of <i>R</i><sup>2</sup> > 0.98. The adjustment factor was determined to be 1.05 times that previously reported. Correlating CAPS extinction to extinction measured by the NEPH + PSAP combination using laboratory-generated polydisperse mixtures of purely scattering ammonium sulfate and highly absorbing black carbon provided a linear regression line with slope <i>m</i> = 1.00 (<i>R</i><sup>2</sup> = 0.994) for single-scattering albedo values (λ = 630 nm) ranging from 0.35 (black carbon) to 1.00 (ammonium sulfate). For ambient aerosol, light extinction measured by CAPS was highly correlated (<i>R</i><sup>2</sup> = 0.995) to extinction measured by the NEPH + PSAP combination with slope <i>m</i> = 0.95.