Intercomparison of a Cavity Attenuated Phase Shift-based extinction monitor (CAPS PMex) with an integrating nephelometer and a filter-based absorption monitor

Abstract

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.

The IAGOS-CORE aerosol package: instrument design, operation and performance for continuous measurement aboard in-service aircraft

“…The instrument measures the extinction as an absolute instrument. This study is already published by Petzold et al (2013) and the main result is shown in Fig. 5.…”

Vertical distributions of aerosol optical properties during the spring 2016 ARIAs airborne campaign in the North China Plain

“…A method description, including results from laboratory characterization and field deployment, has been reported previously (Massoli et al, 2010). The CAPS extinction and the σ ext measured by the combination of the nephelometer and the PSAP showed a good correlation in both laboratory-generated test particles and ambient aerosols (Petzold et al, 2013). The detailed principles of the CAPS technology, optical path adjustment process, and calibration method can be found in previous studies (Kebabian et al, 2008;Kebabian and Freedman, 2007).…”

Airborne and laboratory studies of an IAGOS instrumentation package containing a modified CAPS particle extinction monitor

“…As stated before, the technology has already been assessed both using optical closure approaches and in comparison with Mie theory (Massoli et al 2010;Petzold et al 2013b). While all previous studies were performed at ground pressure, the operation on board aircraft requires a feasibility study at low pressure.…”

“…The modulation frequency is usually set to 17 kHz which provides an initial phase shift of [35][36][37][38][39][40] if the mirrors are clean. The time response of the monitor is 1-2 seconds and, according to Massoli et al (2010) and Petzold et al (2013b), its limit of detection (LOD D 3s where s is the r.m.s. noise for particle-free air) ranges between 1-3 Mm ¡1 (1 second sample period), depending on the particular instrument, and decreases as the square root of the sample period to at least 100 seconds.…”

“…The CAPS PMex can be readily applied in mobile sampling systems since it is compact and robust (Kebabian et al 2007), with a relatively low-cost set up. The CAPS PM ex operational principle has been successfully assessed in optical closure studies and deployed at ground pressure conditions with artificially generated and ambient aerosols (Massoli et al 2010;Petzold et al 2013b) and high concentration exhaust aerosols (Yu et al 2011).…”