HR: 11:50h
AN: A52C-06    [Abstracts]
TI: Single Scatter Albedo Monitor for Airborne Particulates
AU: * Kebabian, P L
EM: pkebab@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821-3976, United States
AU: Onasch, T B
EM: onasch@aerodyne
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821-3976, United States
AU: Freedman, A
EM: af@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821-3976, United States
AB: We describe an instrument that simultaneously incorporates measurements of both airborne particle extinction and scattering coefficients and thus single scatter albedo. Based on a cavity enhanced detection technique, cavity attenuated phase shift spectroscopy, the sensor comprises a light emitting diode (LED), an enclosed measurement cell (25 cm in length) incorporating a resonant optical cavity of near-confocal design (which provides a pathlength of ~ 1km) and a vacuum photodiode to detect extinction and a photomultiplier tube to detect scattering. An extinction coefficient noise floor of approximately 0.3 Mm^-1 with 60 seconds integration time was established measuring Rayleigh scattering of nitrogen. In order to minimize the possibility of measurement bias as a function of particle size, the optical cavity is enclosed in an integrating volume, ensuring reasonably efficient collection of scattered light from all angles. To verify this, simultaneous measurements of extinction and scattering using polystyrene latex (PSL) particles of diameters ranging from 0.1 to 8 μm were performed. The results indicated that the monitor response to scattering as a function of particle size is flat from 0.1 to 2 μm and falls off to 75% of full response at 8 μm. Extensive modeling indicates that this performance is likely limited by the relatively crude construction of the integrating volume and can readily be improved.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting