Measurement and modeling of the multi-wavelength optical properties ofuncoated flame-generated soot

Journal Article · Wed Aug 22 00:00:00 EDT 2018 · Atmospheric Chemistry and Physics Discussions (Online)

DOI:https://doi.org/10.5194/acp-2018-306· OSTI ID:1466609

Forestieri, Sara D. ^[1]; Helgestad, Taylor M. ^[1]; Lambe, Andrew ^[2]; Renbaum-Wolff, Lindsay ^[3]; Lack, Daniel A. ^[4]; Massoli, Paola ^[3]; Cross, Eben S. ^[5]; Dubey, Manvendra K. ^[6]; Mazzoleni, Claudio  ^[7]; Olfert, Jason ^[8]; Sedlacek, III, Arthur J. ^[9]; Freedman, Andrew  ^[3]; Davidovits, Paul ^[10]; Onasch, Timothy B.  ^[2]; Cappa, Christopher D.  ^[1]

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1. Univ. of California, Davis, CA (United States)
2. Aerodyne Research Inc., Billerica, MA (United States); Boston College, Chestnut Hill, MA (United States)
3. Aerodyne Research Inc., Billerica, MA (United States)
4. National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States). Earth System Research Lab.; Univ. of Colorado, Boulder, CO (United States)
5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
6. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
7. Michigan Technological Univ., Houghton, MI (United States)
8. Univ. of Alberta, Edmonton, AB (Canada)
9. Brookhaven National Lab. (BNL), Upton, NY (United States)
10. Boston College, Chestnut Hill, MA (United States)

Abstract. Optical properties of flame-generated black carbon (BC) containing soot particles were quantified at multiple wavelengths for particles produced using two different flames, a methane diffusion flame and an ethylene premixed flame. Measurements were made for: (i) nascent soot particles, (ii) thermally denuded nascent particles, and (iii) particles that were coated then thermally denuded, leading to collapse of the initially lacy, fractal-like morphology. The measured mass absorption coefficients (MAC) depended on soot maturity and generation, but were similar between flames for similar conditions. For mature soot, here corresponding to particles with volume-equivalent diameters >~160nm, the MAC and absorption Angstrom exponent values were independent of particle collapse while the single scatter albedo increased. The MAC values for these larger particles were also size-independent. Effective, theory-specific complex refractive index (RI) values are derived from the observations with two widely-used methods: Lorenz-Mie theory and the Rayleigh-Debye-Gans (RDG) approximation. Mie theory systematically under-predicts the observed absorption cross-sections at all wavelengths for larger particles (with x>0.9) independent of the complex RI used, while RDG provides good agreement. Importantly, this implies that the use of Mie theory within air quality and climate models, as is common, likely leads to under-predictions in the absorption by BC, with the extent of under-prediction depending on the assumed BC size distribution and complex RI used. We suggest that it is more appropriate to assume a constant, size-independent (but wavelength-specific) MAC to represent absorption by uncoated BC particles within models.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: SC0012704
• OSTI ID: 1466609
• Report Number(s): BNL-207979-2018-JAAM
• Journal Information: Atmospheric Chemistry and Physics Discussions (Online), Vol. 18; ISSN 1680-7375
• Publisher: European Geosciences Union
• Country of Publication: United States
• Language: English

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54 ENVIRONMENTAL SCIENCES