Low-cost, Fast-response Aerosol Optical Extinction Monitor

Andrew Freedman Aerodyne Research, Inc.
Paola Massoli Aerodyne Research, Inc.
Paul Kebabian Aerodyne Research, Inc.
Timothy Onasch Aerodyne Research, Inc.

Category: Aerosol Properties

Working Group: Aerosol Life Cycle

We present laboratory and field measurements of aerosol light extinction performed at 445 nm and 632 nm using an instrument that employs Cavity Attenuated Phase Shift (CAPS) technique. The CAPS extinction monitor comprises a light emitting diode (LED), an optical cavity that acts as the sample cell, and a vacuum photodiode for light detection. The particle extinction is determined from changes in the phase shift of the distorted waveform of the square-wave modulated LED light that is transmitted through the cavity. The detection limit (3σ) of the monitor under dry particle-free air is ~3 Mm-1 for 1s integration time. Laboratory measurements of absolute particle extinction cross-sections using non-absorbing, monodisperse polystyrene latex (PSL) spheres were made with an average precision of ±2–4% (2σ); comparison of these results with Mie scattering calculations indicated that these results were accurate within the 10% uncertainty stated for the particle number density measurements. The CAPS extinction monitor was deployed twice in 2009 to test its robustness and performance outside of the laboratory. During these field campaigns, a collocated Multi-Angle Absorption Photometer (MAAP) provided particle light absorption coefficient, allowing an estimate of the single-scattering albedo of the ambient aerosol particles by combining the CAPS-based extinction measurements at 632 nm with the MAAP-based absorption measurements at 635 nm. Our initial results show the high potential of the CAPS as a lightweight, compact instrument to perform precise and accurate extinction measurements of atmospheric aerosols in both laboratory and field conditions.

This poster will be displayed at ASR Science Team Meeting.