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The Reno Aerosol Optics Study: An evaluation of aerosol absorption measurement methods

Sheridan, Patrick J. and Arnott, W. Patrick and Ogren, John A. and Andrews, Elisabeth and Atkinson, Dean B. and Covert, David S. and Moosmüller, Hans and Petzold, Andreas and Strawa, Anthony W. and Schmid, Beat and Varma, Ravi and Virkkula, Aki (2005) The Reno Aerosol Optics Study: An evaluation of aerosol absorption measurement methods. Aerosol Science and Technology, 39, pp. 1-16. DOI: 10.1080/027868290901891.

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Abstract

The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative humidity conditions and delivered to each measurement system. The aerosol mixing and delivery system was constantly monitored using particle counters and nephelometers to ensure that the same aerosol number concentration and amount reached the different instruments. The aerosol light-scattering measurements of four different nephelometers were compared, while the measurements of seven light-absorption instruments (5 filter based, 2 photoacoustic) were evaluated. Four methods for determining the aerosol lightextinction coefficient (3 cavity ring-down instruments and 1 folded path optical extinction cell) were also included in the comparisons. An emphasis was placed on determining the representativeness of the filter-based light absorption methods, since these are used widely and because major corrections to the raw attenuation measurements are known to be required. The extinction measurement from the optical extinction cell was compared with the scattering measurement from a high-sensitivity integrating nephelometer on fine, nonabsorbing ammonium sulfate aerosols, and the two were found to agree closely (within 1% for blue and green wavelengths and 2% for red). The wavelength dependence of light absorption for small kerosene and diesel soot particles was found to be very near λ<sup>−1</sup>, the theoretical small-particle limit. Larger, irregularly shaped graphite particles showed widely variable wavelength dependencies over several graphite runs. The light-absorption efficiency at a wavelength of 530 nm for pure kerosene soot with a number size distribution peak near 0.3 μm diameter was found to be 7.5 +/- 1.2 m<sup>2</sup> g<sup>−1</sup>. The two most fundamental independent absorption methods used in this study were photoacoustic absorption and the difference between suspended-state light extinction and scattering, and these showed excellent agreement (typically within a few percent) on mixed black/white aerosols, with the photoacoustic measurement generally slightly lower. Excellent agreement was also observed between some filter-based light-absorption measurements and the RAOS reference absorption method. For atmospherically relevant levels of the aerosol light-absorption coefficient (less than 25 Mm<sup>−1</sup>), the particle soot absorption photometer (PSAP) absorption measurement at mid-visible wavelengths agreed with the reference absorption measurement to within 11% for experiment tests on externally mixed kerosene soot and ammonium sulfate. At higher absorption levels (characterized by lower single-scattering albedo aerosol tests), this agreement worsened considerably, most likely due to an inadequate filter loading correction used for the PSAP. The PSAP manufacturer’s filter loading correction appears to do an adequate job of correcting the PSAP absorption measurement at aerosol single-scattering albedos above 0.80–0.85, which represents most atmospheric aerosols, but it does a progressively worse job at lower single-scattering albedos.Anew filter-based light-absorption photometer was also evaluated inRAOS, the multiangle absorption photometer (MAAP), which uses a two-stream radiative transfer model to determine the filter and aerosol scattering effects for a better calculation of the absorption coefficient. The MAAP absorption measurements agreed with the reference absorption measurements closely (linear regression slope of 0.99) for all experimental tests on externally mixed kerosene soot and ammonium sulfate.

Document Type:Article
Title:The Reno Aerosol Optics Study: An evaluation of aerosol absorption measurement methods
Authors:
AuthorsInstitution or Email of Authors
Sheridan, Patrick J.NOAA, Boulder, CO, USA
Arnott, W. PatrickDesert Research Institute, Reno, NV, USA
Ogren, John A.NOAA, Boulder, CO, USA
Andrews, ElisabethUniv. of Colorado, Boulder, CO, USA
Atkinson, Dean B.Portland State Univ., Portland, OR, USA
Covert, David S.Univ. of Washington, Seattle, WA, USA
Moosmüller, HansDesert Research Institute, Reno, NV, USA
Petzold, AndreasUNSPECIFIED
Strawa, Anthony W.NASA Ames Research Center, Moffett Field, CA, USA
Schmid, BeatBay Area Environmental Research Inst., Sonoma, CA, USA
Varma, RaviDesert Research Institute, Reno, NV, USA
Virkkula, AkiFinnish Meteorological Inst., Helsinki, F
Date:February 2005
Journal or Publication Title:Aerosol Science and Technology
Volume:39
DOI:10.1080/027868290901891
Page Range:pp. 1-16
Status:Published
Keywords:aerosol measurement, aerosol absoprtion, absorption measurement, multi-angle absorption photometry, RAOS
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Transport
HGF - Program Themes:V UR - Schonung von Umwelt und Ressourcen (old)
DLR - Research area:Transport
DLR - Program:V UR - Schonung von Umwelt und Ressourcen
DLR - Research theme (Project):V - Umweltwirkungen des Verkehrs (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Dr.rer.nat. Andreas Petzold
Deposited On:17 Apr 2007
Last Modified:12 Dec 2013 20:08

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