10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
MultiPAS-IV: A Portable, Four-wavelength Photoacoustic Spectrometer for Ambient Aerosol Absorption
GEOFFREY SMITH, Al Fischer, University of Georgia
Abstract Number: 851 Working Group: Instrumentation
Abstract We have developed a portable, four-wavelength, single-cell photoacoustic spectrometer for simultaneous measurement of aerosol absorption at 406, 532, 662, and 785 nm, with an additional extinction measurement at 662 nm via a built-in cavity ringdown spectrometer. The instrument, dubbed MultiPAS-IV, is compact, robust, has low power requirements, and utilizes a multipass optical arrangement to achieve typical detection limits of 0.6 – 0.7 Mm-1 for absorption (2σ, 2-minute average).
Tests with size-selected nigrosin aerosols show agreement with Mie theory calculations to within 2%. Comparison with a 7-wavelength aethalometer shows good correlation but poor agreement for ambient (Athens, Georgia) aerosols, indicating potential multiple scattering artifacts with the filter-based aethalometer.
We demonstrate the utility of the broad spectral coverage and sensitivity of the MultiPAS-IV for calculating the absorption Ångström exponent of black carbon (AÅEBC, median value of 0.70) in ambient aerosols. Importantly, the single cell design of the instrument allows this value to be derived independent of calibration. The AÅEBC is also used to derive the contribution of brown carbon to absorption at 406 nm (43%) and 532 nm (13%) and its wavelength dependence (AÅEBrC = 6.3).