An Inter-Comparison of Instruments Measuring Black Carbon Content of Soot Particles

Inter-comparison studies of well-characterized fractal soot particles were conducted using the following four instruments: Aerosol Mass Spectrometer-Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Multi-Angle Absorption Photometer (MAAP), and Photoacoustic Spectrometer (PAS). These instruments provided measurements of the refractory mass (AMS-SMPS), incandescent mass (SP2) and optically absorbing mass (MAAP and PAS). The particles studied were in the mobility diameter range from 150 nm to 460 nm and were generated by controlled flames with fuel equivalence ratios ranging between 2.3 and 3.5. The effect of organic coatings (oleic acid and anthracene) on the instrument measurements was determined. For uncoated soot particles, the mass measurements by the AMS-SMPS, SP2, and PAS instruments were in agreement to within 15%, while the MAAP measurement of optically-absorbing mass was higher by ∼ 50%. Thin organic coatings (∼ 10 nm) did not affect the instrument readings. A thicker (∼ 50 nm) oleic acid coating likewise did not affect the instrument readings. The thicker (∼60 nm) anthracene coating did not affect the readings provided by the AMS-SMPS or SP2 instruments but increased the reading of the MAAP instrument by ∼ 20% and the reading of the PAS by ∼ 65%. The response of each instrument to the different particle types is discussed in terms of particle morphology and coating material.

Acknowledgments

Funding for this work was provided by the National Air and Space Administration (NASA) through the Upper Atmosphere Research Program contract NAG2-1462 and the Atmospheric Chemistry Program contract NNH04CC09C, by the Atmospheric Chemistry Program of the National Science Foundation (NSF) grant Nos. ATM-0212464 and ATM-0525355, by the Office of Biological and Environmental Research of the Department of Energy (Atmospheric Science Program) grant Nos. DE-FG02-98ER62581 and DE-FG02-05ER63995. JGS and ESC were funded by the NASA Earth System Science Fellowship program. JPS, RSG, and DWF were supported by the National Oceanic and Atmospheric Administration Climate Program. The SP2 was developed under an SBIR grant from the Office of Naval Research, No. N00014-01-C-0335, to Droplet Measurement Technologies. The contributions of the Desert Research Institute were supported in part by the DOE Atmospheric Science Program under grant DE-FG02-05ER64008, with additional support for instrument development from NSF under grants ATM-0340423 and ATM-9871192. The contribution of AP to the study was supported by the European project AERONET under contract No. ACA3-CT-2003-502882.

Notes

¹As is discussed in the recent review by Bond and Bergstrom (2006), the nomenclature for the light-absorbing, refractory component of carbonaceous aerosols is not clearly established. The term “black carbon” is often used in connection with the light-absorbing properties of the aerosol, while “elemental carbon” is often used when thermal properties are considered. Other terms, such as “graphitic carbon,” which addresses properties of carbon atoms in a graphitic lattice, are also in use.

²The complete set of selected d _m values is as follows: Uncoated soot: at φ = 2.3, d _m ∼ 185, 250, 285, 320, 460; at φ = 2.8, d _m ∼ 110, 175, 190, 220, 285, 340, 345, 420, 460; at φ = 3.5, d _m ∼ 170, 220, 245, 260, 330, 345, 460; at φ = 5.0, d _m ∼ 160, 210, 270, 330, 345; at φ = 6.0, d _m ∼ 160, 335. For thin OA, thin AN, and thick AN coatings: at φ = 2.3, 2.8, and 3.5, d _m ∼ 180, 240, 345; at φ = 5.0, d _m ∼ 345. For thick OA coatings: at φ = 2.3, 2.8, 3.5, and 5.0, d _m ∼ 230, 470.