Soot superaggregates from flaming wildfires and their direct radiative forcing

Chakrabarty, Rajan K.; Beres, Nicholas D.; Moosmüller, Hans; China, Swarup; Mazzoleni, Cláudio; Dubey, Manvendra K.; Liu, Li; Mishchenko, Michael I.

doi:10.1038/srep05508

Cited by 105 publications

(94 citation statements)

References 56 publications

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“…3), similar to those observed from several wildfires in Chakrabarty et al (2014) and from a laboratory fire in Kearney and Pierce (2012). Superaggregates tend to have larger mobility diameters than smaller particles; however, they have low aerodynamic diameters (a measure of their terminal settling velocity), lower effective densities, and are more porous, causing different behavior than primary particles or smaller aggregates (Chakrabarty et al, 2014;Kulkarni et al, 2011a). In Chakrabarty et al (2014), superaggregates were collected in the third stage of an aerosol impactor with a cut point of < 0.3 µm aerodynamic diameter (D a ).…”

Section: Introductionsupporting

confidence: 86%

“…Preliminary images of the filters from scanning electron microscopy (SEM) seemed to support the hypothesis that these large particles were fire-generated superaggregates (Fig. 3), similar to those observed from several wildfires in Chakrabarty et al (2014) and from a laboratory fire in Kearney and Pierce (2012). Superaggregates tend to have larger mobility diameters than smaller particles; however, they have low aerodynamic diameters (a measure of their terminal settling velocity), lower effective densities, and are more porous, causing different behavior than primary particles or smaller aggregates (Chakrabarty et al, 2014;Kulkarni et al, 2011a).…”

Section: Introductionsupporting

confidence: 65%

“…Soot particles are fractal-like, chain aggregates produced from incomplete combustion (Kulkarni et al, 2011a;Wang et al, 2017). Large-scale, turbulent fires provide vortices where soot aggregates (∼ 100 s of monomers) can be trapped in a high particle to volume area, creating superaggregates consisting of thousands of monomers (Chakrabarty et al, 2014;Kearney and Pierce, 2012;Kulkarni et al, 2011a).…”

Section: Introductionmentioning

confidence: 99%

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Aggregated particles caused by instrument artifact

et al. 2018

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Abstract. Previous studies have indicated that superaggregates, clusters of aggregates of soot primary particles, can be formed in large-scale turbulent fires. Due to lower effective densities, higher porosity, and lower aerodynamic diameters, superaggregates may pass through inlets designed to remove particles < 2.5 µm in aerodynamic diameter (PM 2.5 ). Ambient particulate matter samples were collected at Peavine Peak, NV, USA (2515 m) northwest of Reno, NV, USA from June to November 2014. The Teledyne Advanced Pollution Instrumentation (TAPI) 602 Beta Plus particulate monitor was used to collect PM 2.5 on two filter types. During this time, aggregated particles > 2.5 µm in aerodynamic diameter were collected on 36 out of 158 sample days. On preliminary analysis, it was thought that these aggregated particles were superaggregates, depositing past PM 10 (particles < 10 µm in aerodynamic diameter) pre-impactors and PM 2.5 cyclones. However, further analysis revealed that these aggregated particles were dissimilar to superaggregates observed in previous studies, both in morphology and in elemental composition. To determine if the aggregated particles were superaggregates or an instrument artifact, samples were investigated for the presence of certain elements, the occurrence of fires, high relative humidity and wind speeds, as well as the use of generators on site. Samples with aggregated particles, referred to as aggregates, were analyzed using a scanning electron microscope for size and shape and energy dispersive Xray spectroscopy was used for elemental analysis. It was determined, based on the high amounts of aluminum present in the aggregate samples, that a sampling artifact associated with the sample inlet and prolonged, high wind events was the probable reason for the observed aggregates.

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Section: Introductionsupporting

confidence: 86%

Section: Introductionsupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

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Aggregated particles caused by instrument artifact

et al. 2018

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“…A tunable particle-cluster aggregation algorithm is applied to generate 30 the FAs (Filippov et al, 2000;Liu et al, 2012), and the coating sphere is added with its center located at the mass center of compact FA. Three transmission or scanning electron microscope images of BC particles are also given in the figure for comparison (Burr et al, 2012;Lewis et al, 2009;Freney et al, 2010), and we can see that the numerically generated 1997; Sorensen, 2000;Brasil et al, 2000;Chakrabarty et al, 2014) have been widely used for numerical studies, and are applied here to represent realistic BC particles (Liu and Mishchenko, 2005;Smith and Grainger, 2014;Li et al, 2016). The diameter of the same-sized monomers is set to 30 nm, and the fractal prefactor of 1.2 is used.…”

Section: Bc Geometrymentioning

confidence: 99%

The Absorption Ångström Exponent of black carbon: from numerical aspects

Liu¹,

Chung²,

Yin³

2017

Preprint

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Abstract. The Absorption Ångström Exponent (AAE) is an important aerosol optical parameter used for aerosol 10 characterization and apportionment studies. The AAE of black carbon (BC) is widely accepted to be 1.0, although observational estimates give a quite wide range of 0.6~1.1. With considerable uncertainties related to observations, a numerical study is a powerful method, if not the only one, to provide a better and more accurate understanding on BC AAE.This study calculates BC AAE using realistic particle geometries based on fractal aggregate and an accurate numerical optical model (namely the Multiple-Sphere T-Matrix method). At odds with the expectations, BC AAE is not 1.0, even when 15 BC is assumed to have small sizes and a wavelength independent refractive index. With a wavelength independent refractive index, the AAE of fresh BC is approximately 1.05, and is quite insensitive to particle size distribution. BC AAE goes lower when BC particles are aged (compact structures or coated by other scattering materials). For coated BC, we prescribed the coating thickness distribution based on a published experimental study, where smaller BC cores were shown to develop thicker coating than bigger BC cores. Both Compact and Coated BC the AAE ranges, at realistic particle sizes. For both 20Compact and Coated BC, the AAE is highly sensitive to particle size distribution, ranging from approximately 0.8 to 1.0 for relatively large BC with wavelength-independent refractive index. When the refractive index is allowed to vary with wavelength, a feature with observational backing, the BC AAE shows a much wider range. We propose that the presented results herein serve as a comprehensive guide for the response of BC AAE to BC size, refractive index, and geometry.

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“…For example, in general, the rain samples had many larger BC aggregates (> 200 nm), whereas BC aggregates found in the ice cores were significantly smaller (∼ 100 nm) and displayed a much more compact structure. Rain samples also contained numerous superaggregates as described in (Chakrabarty et al, 2014). These superaggregates were > 1 µm in diameter and were absent in the ice cores (Fig.…”

Section: Transmission Electron Microscopymentioning

confidence: 67%

Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy

et al. 2015

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Abstract. Antarctic ice cores have been used to study the history of black carbon (BC), but little is known with regards to the physical and chemical characteristics of these particles in the remote atmosphere. Characterization remains limited by ultra-trace concentrations in ice core samples and the lack of adequate methods to isolate the particles unaltered from the melt water. To investigate the physical and chemical characteristics of these particles, we have developed a tangential flow filtration (TFF) method combined with transmission electron microscopy (TEM). Tests using ultrapure water and polystyrene latex particle standards resulted in excellent blanks and significant particle recovery. This approach has been applied to melt water from Antarctic ice cores as well as tropical rain from Darwin, Australia with successful results: TEM analysis revealed a variety of BC particle morphologies, insoluble coatings, and the attachment of BC to mineral dust particles. The TFF-based concentration of these particles has proven to give excellent results for TEM studies of BC particles in Antarctic ice cores and can be used for future studies of insoluble aerosols in rainwater and ice core samples.

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Soot superaggregates from flaming wildfires and their direct radiative forcing

Cited by 105 publications

References 56 publications

Aggregated particles caused by instrument artifact

Aggregated particles caused by instrument artifact

The Absorption Ångström Exponent of black carbon: from numerical aspects

Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy

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