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Continuous-Wave Cavity Ring-Down Measurement of Aerosol Optical Properties

Strawa, A.(a), Schmid, B.(b), Owano, T.(c), and Provencal, R.(d), NASA Ames Research Center (a), Bay Area Environmental Research Inst. (b), Los Gatos Research Inc. (c), Picarro Inc. (d)
Thirteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting

Large uncertainties in the effects that aerosols have on climate require improved in-situ measurements of extinction coefficient and single-scattering albedo. This paper will describe the use of continuous wave cavity ring-down (CW-CRD) technology to address this problem. The innovations in this instrument are the use of CW-CRD to measure aerosol extinction coefficient, the simultaneous measurement of scattering coefficient, and its small size which makes it suitable for a wide range of aircraft applications. Our prototype instrument measures extinction and scattering coefficient at 690 nm and extinction coefficient at 1550 nm. The instrument itself is small (60 x 48 x 15 cm) and relatively insensitive to vibrations. The prototype instrument has been tested in our lab and used in the field. While improvements in performance are needed, the prototype has been shown to make accurate and sensitive measurements of extinction and scattering coefficients. Combining these two parameters, one can obtain the single-scattering albedo and absorption coefficient, both important aerosol properties. Minimum sensitivity of the prototype instrument is 1.5x10-6 m-1 (1.5 Mm-1). Validation of the measurement of extinction coefficient has been accomplished by comparing the measurement of calibration spheres with Mie calculations. This instrument and its successors have potential to help reduce uncertainty currently associated with aerosol optical properties and their spatial and temporal variation. Possible applications include studies of visibility, climate forcing by aerosol, and the validation of aerosol retrieval schemes from satellite data.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).