Design and application of a pulsed cavity ring-down aerosol extinction spectrometer for field measurements

This paper describes the design and application of a pulsed cavity ring-down aerosol extinction spectrometer (CRD-AES) for in-situ atmospheric measurement of the aerosol extinction coefficient and its relative humidity dependence. This CRD-AES measures the aerosol extinction coefficient (sigma(ep)) at 355 nm, 532 nm, 683 nm, and 1064 nm with a minimal size dependent bias for particles with diameter less than 10 mu m. The sigma(ep) at 532 urn is measured with an accuracy of 1% when extinction is >= 10 Mm(-1). The precision is limited by statistical fluctuations within the small optical volume and the time resolution of extinction at 2% uncertainty for various air mass types is evaluated. The CRD-AES is configured with two separate cavity ring-down cells for measurement of the extinction coefficient at 532 nm. This allows the determination of the RH dependence of extinction at 532 nm through independent RH control of the sample for each measurement. Gas phase absorption and minimization of potential interferences is also considered.