Variation of the optical properties of soot as a function of particle mass

Dastanpour, Ramin; Momenimovahed, Ali; Thomson, Kevin A.; Olfert, Jason S.; Rogak, Steven N.

doi:10.1016/j.carbon.2017.07.005

Cited by 47 publications

(42 citation statements)

References 53 publications

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“…Some particle size dependence was reported by Khalizov et al (2009), who used propane with a Santoro-type burner, with reported MACs at λ = 532 nm of 6.7 ± 0.7 m 2 g −1 for d m = 155 nm particles and 8.7±0.1 m 2 g −1 for d m = 320 nm particles. This general behavior was also observed for soot particles generated from a methane diffusion flame in Dastanpour et al (2017), with MAC values reported at λ = 660 nm of ∼ 5 m 2 g −1 for d p,VED = 50 nm and ∼ 7 m 2 g −1 for d p,VED = 100 nm. One key reason that differences may exist between studies is that the BC particles sampled had differing maturity.…”

Section: Comparison Of Measured and Calculated Mac Valuessupporting

confidence: 75%

“…This could indicate that, at some point, further changes in the soot maturity (composition) have no influence at short wavelengths but do at longer wavelengths. As a complementary explanation, Dastanpour et al (2017) observed an increase in primary spherule size with overall particle size for methane-diffusion-flame-generated soot. They attribute the increase in MAC with d p,VED to changes in the internal structure and/or the degree of graphitization that occur with changes in spherule size.…”

Section: Comparison Of Measured and Calculated Mac Valuesmentioning

confidence: 90%

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Measurement and modeling of the multiwavelength optical properties of uncoated flame-generated soot

et al. 2018

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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 and then thermally denuded, leading to the collapse of the initially lacy, fractal-like morphology. The measured mass absorption coefficients (MACs) 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 >∼ 160 nm, the MAC and absorption Ångström exponent (AAE) values were independent of particle collapse while the single-scatter albedo increased. The MAC values for these larger particles were also size-independent. The mean MAC value at 532 nm for larger particles was 9.1 ± 1.1 m 2 g −1 , about 17 % higher than that recommended by Bond and Bergstrom (2006), and the AAE was close to unity. 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 underpredicts 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. (The dimensionless size parameter x = π d p /λ, where d p is particle diameter and λ is wavelength.) Importantly, this implies that the use of Mie theory within air quality and climate models, as is common, likely leads to underpredictions in the absorption by BC, with the extent of underprediction 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.

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Section: Comparison Of Measured and Calculated Mac Valuessupporting

confidence: 75%

Section: Comparison Of Measured and Calculated Mac Valuesmentioning

confidence: 90%

Measurement and modeling of the multiwavelength optical properties of uncoated flame-generated soot

et al. 2018

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“…An accurate estimate of the BC radiative effects requires the incorporation of the aging process and coating structure [65,66] and consideration of particle mass [67]. This current work was focused on freshly emitted biomass burning aerosols.…”

Section: Resultsmentioning

confidence: 99%

Optical Properties of Biomass Burning Aerosols: Comparison of Experimental Measurements and T-Matrix Calculations

et al. 2017

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Abstract:The refractive index (RI) is an important parameter in describing the radiative impacts of aerosols. It is important to constrain the RI of aerosol components, since there is still significant uncertainty regarding the RI of biomass burning aerosols. Experimentally measured extinction cross-sections, scattering cross-sections, and single scattering albedos for white pine biomass burning (BB) aerosols under two different burning and sampling conditions were modeled using T-matrix theory. The refractive indices were extracted from these calculations. Experimental measurements were conducted using a cavity ring-down spectrometer to measure the extinction, and a nephelometer to measure the scattering of size-selected aerosols. BB aerosols were obtained by burning white pine using (1) an open fire in a burn drum, where the aerosols were collected in distilled water using an impinger, and then re-aerosolized after several days, and (2) a tube furnace to directly introduce the BB aerosols into an indoor smog chamber, where BB aerosols were then sampled directly. In both cases, filter samples were also collected, and electron microscopy images were used to obtain the morphology and size information used in the T-matrix calculations. The effective radius of the particles collected on filter media from the open fire was approximately 245 nm, whereas it was approximately 76 nm for particles from the tube furnace burns. For samples collected in distilled water, the real part of the RI increased with increasing particle size, and the imaginary part decreased. The imaginary part of the RI was also significantly larger than the reported values for fresh BB aerosol samples. For the particles generated in the tube furnace, the real part of the RI decreased with particle size, and the imaginary part was much smaller and nearly constant. The RI is sensitive to particle size and sampling method, but there was no wavelength dependence over the range considered (500-680 nm). Our values for the RI of fresh (white pine) biomass burning aerosols ranged from 1.33 + i0.008 to 1.74 + i0.008 for 200-nm, 300-nm, and 400-nm diameter particles. These are within the range of RI values in the most recent study conducted during the Fire Laboratory at Missoula Experiments (FLAME I and II), which were 1.55 to 1.80 for the real part, and 0.01-0.50 for the imaginary part, for fresh BB aerosols with diameters of 200-570 nm. There is no clear trend on the dependence of the RI values on particle size. The RI values derived from measurements of aerosols produced from the combustion of hydrocarbons and diesel cannot be used for BB aerosols.

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“…This could indicate that, at some point, further changes in the soot maturity (composition) have no influence at short wavelengths, but do at longer wavelengths. As a complementary explanation, Dastanpour et al (2017) observed an increase in primary spherule size with overall particle size for methane diffusion flame generated soot. They attribute the increase in MAC with dp,VED to changes in the internal structure and/or the degree of graphitization that occur with 15 changes in spherule size.…”

Section: Comparison Of Measured and Calculated Mac Valuesmentioning

confidence: 90%

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

Forestieri¹,

Helgestad²,

Lambe³

et al. 2018

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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 25 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 30 volume-equivalent diameters > ~160 nm, the MAC and absorption Angstrom exponent values Atmos. Chem. Phys. Discuss., https://doi

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Variation of the optical properties of soot as a function of particle mass

Cited by 47 publications

References 53 publications

Measurement and modeling of the multiwavelength optical properties of uncoated flame-generated soot

Measurement and modeling of the multiwavelength optical properties of uncoated flame-generated soot

Optical Properties of Biomass Burning Aerosols: Comparison of Experimental Measurements and T-Matrix Calculations

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

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