Soot Particle Studies—Instrument Inter-comparison

Timothy Onasch Aerodyne Research, Inc.
Eben Cross Massachusetts Institute of Technology
Douglas Worsnop Aerodyne Research, Inc.
Charles Kolb Aerodyne Research, Inc.
Paul Davidovits Boston College

Category: Aerosol Properties

Working Group: Aerosol Life Cycle

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Absorption cross-sections (σabs) for denuded soot measured at λ = 532 nm for the (a) PASS-3, (b) PTI, and (c) PAS instruments as a function of the mass measured by the CPMA instrument. Soot particles were generated at φ = 2.0 0.2. The symbols indicate the different coating condition (prior to denuding): DOS-coated-denuded (squares), H2SO4-coated-denuded (circles), or nascent-denuded (stars). The linear regressions shown are fit through all three denuded particle types (weighted to the 1σ standard deviations shown). The slope of each linear fit is the mass specific absorption coefficient (MAC).

An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer-Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS), and Photoelectric Aerosol Sensor (PAS2000CE). The following optical absorption measuring instruments were tested: Photoacoustic Spectrometer (PAS), Photoacoustic Soot Spectrometer (PASS-3), and Photo-Thermal Interferometer (PTI). Optical extinction measuring instruments tested were: Cavity Ring Down Aerosol Extinction Spectrometer (CRD-AES) and Cavity Attenuated Phase Shift Extinction Monitor (CAPS). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤ φ ≤ 5), particle shape (fractal dimension 1.8 ≤ Df ≤ 3.0), particle mobility size (30 ≤ dm ≤ 300 nm), black carbon mass (0.07 ≤ mBC ≤ 4.2 fg), and particle chemical composition. In selected runs, particles were coated with sulfuric acid or di-octyl sebacate (DOS) (0.5 ≤ Δrve ≤ 201 nm). The effect of non-absorbing coatings on instrument response was determined. Changes in the morphology of fractal soot particles were monitored during coating and denuding processes, and the effect of particle shape on instrument response was determined. The combination of optical and mass-based measurements was used to determine the mass-specific absorption coefficient for denuded soot particles. The single-scattering albedo of the particles was also measured. An overview of the experiments and sample results are presented. As an example of the data obtained, the figure displays optical absorption cross section (σabs) at λ = 532 nm as a function of per-particle black carbon mass for denuded soot measured with the PASS-3, PTI, and PAS instruments. Three types of denuded particles are shown in the figure: DOS-coated-denuded (squares), H2SO4-coated-denuded (circles), and nascent-denuded (stars). The slope of each linear fit is the mass specific absorption coefficient (MAC) as noted in the figure. * Thirty scientists from 14 institutions participated in the study. Only a partial list of authors is provided in this abstract. The full list of authors is shown in the poster.

This poster will be displayed at ASR Science Team Meeting.

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