Formation of refractory black carbon by SP2-induced charring of organic aerosol

Sedlacek, Arthur J.; Onasch, T. B.; Nichman, Leonid; Lewis, Ernie R.; Davidovits, P.; Freedman, Andrew; Williams, Leah R.

doi:10.1080/02786826.2018.1531107

Cited by 25 publications

(36 citation statements)

References 19 publications

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“…Intensity profiles of the diffraction patterns were obtained by both azimuthal integration along rings and background correction using PASAD-tools (Gammer et al, 2010). For comparison a simulated profile of graphite was calculated with JEMS software (Stadelmann, 2004).…”

Section: Tem -Transmission Electron Microscopymentioning

confidence: 99%

Structural changes of CAST soot during a thermal–optical measurement protocol

et al. 2019

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Abstract. Thermal–optical measurement techniques are widely used to classify carbonaceous material. The results of different methods for total carbon are comparable but can vary by >44 % for elemental carbon. One major cause of variation is the formation of pyrolyzed carbon during the heating process which occurs mainly in samples with a high amount of brown carbon (BrC). In this study the structural changes of two different CAST (combustion aerosol standard) aerosol samples caused by the heating procedure in a thermal–optical instrument were investigated with UV–VIS and Raman spectroscopy, the integrating-sphere technique (IS) and transmission electron microscopy. All analysis techniques showed significant structural changes for BrC-rich samples at the highest temperature level (870 ∘C) in helium. The structure of the heated BrC-rich sample resembles the structure of an unheated BrC-poor sample. Heating the BrC-rich sample to 870 ∘C increases the graphitic domain size within the material from 1.6 to 2 nm. Although the Raman spectra unambiguously show this increase in ordering only at the highest temperature step, UV–VIS and IS analyses show a continuous change in the optical properties also at lower temperatures. The sample with a negligible amount of BrC, however, did not show any significant structural changes during the whole heating procedure.

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Section: Tem -Transmission Electron Microscopymentioning

confidence: 99%

Structural changes of CAST soot during a thermal–optical measurement protocol

et al. 2019

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“…In laboratory BB experiments, some OA has been shown to absorb in the red with a steep rise in the blue (Chakrabarty et al, 2010; China et al, 2013; Hand et al, 2005; Hoffer et al, 2017; Sedlacek et al, 2018). OA with these characteristics has been hypothesized to be related to “tar balls,” spherical, carbonaceous particles observed by electron microscopy (Chakrabarty et al, 2010; Hand et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Optical and Chemical Analysis of Absorption Enhancement by Mixed Carbonaceous Aerosols in the 2019 Woodbury, AZ, Fire Plume

et al. 2020

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Wildfires emit mixtures of light‐absorbing aerosols (including black and brown carbon, BC and BrC, respectively) and more purely scattering organic aerosol (OA). BC, BrC, and OA interactions are complex and dynamic and evolve with aging in the atmosphere resulting in large uncertainties in their radiative forcing. We report microphysical, optical, and chemical measurements of multiple plumes from the Woodbury Fire (AZ, USA) observed at Los Alamos, NM, after 11–18 hr of atmospheric transit. This includes periods where the plumes exhibited little entrainment as well as periods that had become more dilute after mixing with background aerosol. Aerosol mass absorption cross sections (MAC) were enhanced by a factor of 1.5–2.2 greater than bare BC at 870 nm, suggesting lensing by nonabsorbing coatings following a core‐shell morphology. Larger MAC enhancement factors of 1.9–5.1 at 450 nm are greater than core‐shell morphology can explain and are attributed to BrC. MAC of OA (MACOrg) at 450 nm was largest in intact portions of the plumes (peak value bounded between 0.6 and 0.9 m2/g [Org]) and decreased with plume dilution. We report a strong correlation between MACOrg(450 nm) with the fC2H4O2 (a tracer for levoglucosan‐like species) of coatings and of bulk OA indicating that BrC in the Woodbury Fire was coemitted with levoglucosan, a primary aerosol. fC2H4O2 and MACOrg(450 nm) are shown to vary between the edge and the core of plumes, demonstrating enhanced oxidation of OA and BrC bleaching near plume edges. Our process‐level finding can inform parameterizations of mixed BC, BrC, and OA properties for wildfire plumes in climate models.

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“…It must also be mentioned that Pósfai et al (2003) also observed a tarball number fraction of 18 % for a separate unprocessed plume over South Africa, suggesting that atmospheric ageing is not the only mechanism of tarball formation. In a separate study, Sedlacek III et al (2018) also concluded that tarball number and mass fractions increased after about 2 h of ageing. They quantified tar ball number fractions by electron microscopy and tarball mass fractions, under the assumption that their tarballs flash-vaporized at 873 K in an aerosol mass spectrometer (which may not be true for the more processed tarballs which are stable in electron microscopes, as shown for residual-fuel tar particles; .…”

Section: Review Of Tarball Propertiesmentioning

confidence: 91%

“…The formation of tar brC has been proposed to proceed through the thermally or chemically induced polymerization and carbonization of high-molecular-weight organic fuels, including biomass (Pósfai et al, 2004;Tóth et al, 2014;Hoffer et al, 2016a;Sedlacek III et al, 2018) and crudeoil residual fuel . The pyrolysis hypothesis has been directly demonstrated by laboratory studies for both biomass tar (Tóth et al, 2014) and residualfuel tar (Jiang et al, 2019).…”

Section: Review Of Tarball Propertiesmentioning

confidence: 99%

“…Atmospheric light-absorbing carbon (LAC) in particulate matter (PM) plays a substantial role in the radiative balance of the earth both directly and by influencing cloud properties (Boucher et al, 2013). While soot black carbon (soot BC) is the best-recognized form of LAC (Bond et al, 2013), increasing attention has recently been paid to the so-called "brown carbon" (Kirchstetter et al, 2004;Laskin et al, 2015) and "tarballs" (Pósfai et al, 2004;Hand et al, 2005;Niemi et al, 2006;Semeniuk et al, 2006;Tivanski et al, 2007;Alexander et al, 2008;Vernooij et al, 2009;Chakrabarty et al, 2010;Adachi and Buseck, 2011;China et al, 2013;Zhu et al, 2013;Tóth et al, 2014;Hoffer et al, 2016a, b;Sedlacek III et al, 2018; which possess substantially different physical properties than BC. The term brown carbon is canonically used to refer to the collection of substantially light-absorbing organic molecules found in PM, while the term tarballs refers to the insoluble amorphouscarbon spheres which may be produced by the pyrolysis of high-molecular-weight fuels such as biomass (Tóth et al, 2014) or heavy fuel oil .…”

Section: Introductionmentioning

confidence: 99%

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Detection of tar brown carbon with a single particle soot photometer (SP2)

Corbin

Gysel

2019

Atmos. Chem. Phys.

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Abstract. We investigate the possibility that the refractory, infrared-light-absorbing carbon particulate material known as “tarballs” or tar brown carbon (tar brC) generates a unique signal in the scattering and incandescent detectors of a single particle soot photometer (SP2). As recent studies have defined tar brC in different ways, we begin by reviewing the literature and proposing a material-based definition of tar. We then show that tar brC results in unique SP2 signals due to a combination of complete or partial evaporation, with no or very little incandescence. Only a subset of tar brC particles exhibited detectable incandescence (70 % by number); for these particles the ratio of incandescence to light scattering was much lower than that of soot black carbon (BC). At the time of incandescence the ratio of light scattering to incandescence from these particles was up to 2-fold greater than from soot (BC). In our sample, where the mass of tar was 3-fold greater than the mass of soot, this led to a bias of <5 % in SP2-measured soot mass, which is negligible relative to calibration uncertainties. The enhanced light scattering of tar is interpreted as being caused by tar being more amorphous and less graphitic than soot BC. The fraction of the tar particle which does incandesce was likely formed by thermal annealing during laser heating. These results indicate that laser-induced incandescence, as implemented in the SP2, is the only BC measurement technique which can quantify soot BC concentrations separately from tar while also potentially providing real-time evidence for the presence of tar. In contrast, BC measurement techniques based on thermal–optical (EC: elemental carbon) and absorption (eBC: equivalent BC) measurements cannot provide such distinctions. The optical properties of our tar particles indicate a material similarity to the tar particles previously reported in the literature. However, more- and less-graphitized tar samples have also been reported, which may show stronger and weaker SP2 responses, respectively.

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Formation of refractory black carbon by SP2-induced charring of organic aerosol

Cited by 25 publications

References 19 publications

Structural changes of CAST soot during a thermal–optical measurement protocol

Structural changes of CAST soot during a thermal–optical measurement protocol

Optical and Chemical Analysis of Absorption Enhancement by Mixed Carbonaceous Aerosols in the 2019 Woodbury, AZ, Fire Plume

Detection of tar brown carbon with a single particle soot photometer (SP2)

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