Andrew Freedman — Aerodyne Research, Inc.
Timothy B Onasch — Aerodyne Research, Inc.
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Paul L Kebabian — Aerodyne Research, Inc.
Category
Instruments
Description
Schematic of CAPS PM-SSA monitor.
We present results of studies detailing the efficacy of a compact, robust instrument that determines the single-scattering albedo of ambient particles by simultaneously measuring both total extinction and scattering of a common ambient air parcel; measurement wavelengths of 450, 530, and 630 nm are available. Particle extinction is measured using the cavity attenuated phase shift approach as it is in the CAPS PMex monitor. Particle scattering is determined using an inverse nephelometer facilitated by the incorporation of an integrating sphere within measurement volume. This approach, as compared to using a cosine-corrected detector, results in minimal truncation errors— <10% for particles of diameter 1 micron or less and ≤20% for particle diameter of 2.5 microns. Both extinction and scattering can be measured with a time response (10–90%) of ~ 1 second. The short-term noise in both extinction and scattering channels is less than 0.5 Mm-1 with 1-second sampling time. The CAPS PMSSA is designed to operate autonomously, without the need for user intervention or expendables except for occasional calibration of the scattering channel. The scattering channel can be readily calibrated with any available gas that has a larger Rayleigh scattering coefficient than that of air without knowing the actual value.
