Intercomparison of a Cavity Attenuated Phase Shift-based extinction monitor (CAPS PMex) with an integrating nephelometer and a filter-based absorption monitor
Abstract. An evaluation of the Cavity Attenuated Phase Shift particle light extinction monitor (CAPS PMex) 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 PMex 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−1 (10−6 m−1) with a linear correlation coefficient of R2 > 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 m = 1.00 (R2 = 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 (R2 = 0.995) to extinction measured by the NEPH + PSAP combination with slope m = 0.95.