A CAPS-based single-scattering albedo monitor

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Description

We present data detailing the performance of a particle single-scattering albedo (SSA) monitor that incorporates both a CAPS (Cavity Attenuated Phase Shift)-based optical extinction measurement and an inverse nephelometer in the same measurement volume. Since an absolute extinction measurement is provided, the scattering channel can be calibrated with any non-absorbing particle (e.g., a PSL) or gas (other than air). The monitor demonstrates noise levels (1 second sample time) of less than 1 Mm-1 in both channels. Measurements of the single-scattering albedo of bare and organic-coated soot particles using both this monitor (the CAPS PMssa) and another instrument that comprised a cavity ring down-based extinction system with a photoacoustic particle absorption spectrometer (courtesy of C Cappa, UC Davis) showed excellent agreement between the two. The SSA monitor can be operated in any wavelength region compatible with the availability of high-reflectivity mirrors, LEDs, and photomultiplier tube PMT) photocathodes. At present, the available wavelength band is restricted to the 400–700 nm region. The upper value is limited by the availability of a suitable PMT, while at the lower end, the lack of high quality mirrors is the issue.