AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
A Novel Multi-wavelength Photoacoustic-nephelometer Instrument Using a Supercontinuum Light Source for Aerosol Absorption and Scattering Measurements
NOOPUR SHARMA, Ian Arnold, Hans Moosmuller, W. Patrick Arnott, Claudio Mazzoleni, Michigan Technological University
Abstract Number: 293 Working Group: Instrumentation and Methods
Abstract Wavelength dependence of absorption and scattering by atmospheric particles has been studied for decades due to their relevance to climate, air quality and visibility. Absorption of particles like black and organic carbon and mineral dust exhibits different wavelength dependencies often with enhanced absorption toward shorter wavelengths. Methods used to measure the wavelength dependence of light absorption for atmospheric particles include: filter-based light attenuation measurements, photo-thermal interferometers, and photoacoustic spectrometers. While filter-based methods are very common, they present artifacts due to multiple scattering from the filter substrate. These artifacts become particularly difficult to deal with when measuring brown carbon aerosol, which typically exhibits stronger wavelength dependence and may change its morphology upon filter deposition. Therefore, new methods capable of measuring at multiple wavelengths are an active field of research, aiming to reduce uncertainties of atmospheric aerosol optical properties and their effect on radiative forcing and climate.
At Michigan Technological University and the Desert Research Institute (Reno, Nevada), we are developing a novel, multi-wavelength integrated photoacoustic-nephelometer spectrometer. This instrument combines a supercontinuum light source with photoacoustics and nephelometry to measure the absorption and scattering by aerosol particles, currently at five different wavelength bands (centered at 417, 475, 542, 607, and 675 nm). The wavelength bands of interest are selected from the continuous spectrum of the light source using a set of optical interference filters. Measurements on the aerosol sample are performed sequentially at each wavelength band and provide scattering and absorption coefficients simultaneously, allowing the direct calculation of the single scattering albedo at the given wavelength. We present the design and development of the instrument and discuss its performance. We review the results obtained from tests performed on laboratory-generated aerosols, including black carbon and sodium chloride particles.