Enhanced light absorption by mixed source black and brown carbon particles in UK winter

Liu, Shang; Aiken, A. C.; Gorkowski, Kyle; Dubey, Manvendra K.; Cappa, Christopher D.; Williams, Leah R.; Herndon, S. C.; Massoli, P.; Fortner, Edward C.; Chhabra, P. S.; Brooks, W. Abdullah; Onasch, T. B.; Jayne, John T.; Worsnop, Douglas R.; China, Swarup; Sharma, Noopur; Mazzoleni, Cláudio; Xu, Lu; Ng, N. L.; Liu, Dantong; Allan, J. D.; Lee, James; Fleming, Zoë L.; Mohr, Claudia; Zotter, Peter; Szidat, Sönke; Prévôt, Andrê S. H.

doi:10.1038/ncomms9435

Cited by 310 publications

(331 citation statements)

References 60 publications

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“…MAC, a key parameter in our understanding of the net BC climate impact, is indeed a more relevant quantity to examine. A fast MAC enhancement in polluted environments as the BC gets coated with organic and inorganic species is consistent with recent findings (2,3 Coating of BC by soluble species not only enhances absorption of solar radiation but also reduces the BC atmospheric lifetime (7). Fig.…”

supporting

confidence: 75%

Jury is still out on the radiative forcing by black carbon

Boucher

Balkanski

Hodnebrog

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Peng et al. (1) conclude that a fast increase in the mass absorption cross-section (MAC) of black carbon (BC) in urban environments leads to significantly increased estimates of the BC radiative forcing (RF). Their chamber measurements are highly valuable and complement observations performed in ambient conditions, but their "enhancement factor" relative to an unspecified baseline may not be directly comparable to values used or simulated in global aerosol models. MAC, a key parameter in our understanding of the net BC climate impact, is indeed a more relevant quantity to examine. A fast MAC enhancement in polluted environments as the BC gets coated with organic and inorganic species is consistent with recent findings (2, 3). Global models used in AeroCom [table S1 in Peng et al. This value is reflecting reported measurements, although there is a large spatial and seasonal variability in ambient MAC for aged particles, with values of ∼10 m 2 ·g −1 at a rural Northern Chinese site (2) (at 678 nm); 6-14 m 2 ·g −1 at rural, urban, and high-altitude Indian locations (5) (at 678 nm); and ∼6 m 2 ·g −1 at an Arctic site (6) (at 522 nm).Coating of BC by soluble species not only enhances absorption of solar radiation but also reduces the BC atmospheric lifetime (7). Fig. 1 shows an offset between the increase in average MAC value with faster BC aging and an overall shorter BC lifetime, resulting in a nearconstant BC aerosol absorption optical depth and RF with aging time. Furthermore, current global aerosol models frequently have a too long BC lifetime and consequently overestimate BC concentrations downwind from source regions (8).According to Peng et al.(1), their BC absorption enhancement factor of 2.4 is also an upper bound, only reached after 5 (Beijing) to 18 (Houston) h, and possibly longer in cleaner environments. Such timescales are not small compared with the BC atmospheric lifetime of 3-5 d, especially considering that dilution effects may lengthen the aging timescale in the real atmosphere compared with the static chamber measurements performed by Peng et al. It is unclear how representative these measurements are for global and annual averages, but we know that generalizations can introduce serious errors due to spatial and temporal sampling issues (9). This implies that a simple scaling of the BC RF by the absorption enhancement factor measured by Peng et al.-as performed by the authors in their table S1 and figure 4, and extended in the commentary (10)-is overly simplistic.In conclusion, although we welcome the advances made by Peng et al., their conclusion of a +0.45 [0.21-0.80] W·m −2 additional RF due to a large BC enhancement factor is premature. The jury is still out on the question of the net climate impact of BC and how much climate cobenefit will result from the necessary mitigation of BC emissions. Reducing the uncertainty on the BC forcing requires better constraining BC MAC and atmospheric lifetime in global aerosol models.

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supporting

confidence: 75%

Jury is still out on the radiative forcing by black carbon

Boucher

Balkanski

Hodnebrog

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…A complex mixture of gas-phase organic compounds with a wide range of volatilities and molecular structures are co-emitted with BC from vehicles, contributing prominently to the urban SOA burden (Gentner et al, 2017, and references therein). Although it is not straightforward to identify the role of individual SOA precursors, previous studies have shown that organic coating thickness of BC particles and their degree of oxygenation increased with photochemical age or oxidant levels in the atmosphere (Cappa et al, 2012;Liu et al, 2015;Wang et al, 2017). Of particular concern is the timescale that is required for sufficient SOA condensation to modify the physical, chemical, and optical properties of BC near emission sources.…”

Section: Introductionmentioning

confidence: 99%

“…Real-time and mass-based chemical compositions of organic coatings on ambient BC particles were seldom reported until the recent development of an Aerodyne soot-particle aerosol mass spectrometer (SP-AMS; Cappa et al, 2012;Massoli et al, 2012Massoli et al, , 2015Onasch et al, 2012;Liu et al, 2015;Lee et al, 2016;Willis et al, 2016). In this study, we investigate formation of organic coatings on BC particles by deploying a SP-AMS in Fontana, California, which is located in the broader South Coast Air Basin and includes the greater Los Angeles area.…”

Section: Introductionmentioning

confidence: 99%

Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions

Lee

Chen

et al. 2017

Atmos. Chem. Phys.

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Abstract. Black carbon (BC) emitted from incomplete combustion can result in significant impacts on air quality and climate. Understanding the mixing state of ambient BC and the chemical characteristics of its associated coatings is particularly important to evaluate BC fate and environmental impacts. In this study, we investigate the formation of organic coatings on BC particles in an urban environment (Fontana, California) under hot and dry conditions using a soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS was operated in a configuration that can exclusively detect refractory BC (rBC) particles and their coatings. Using the −log(NO x / NO y ) ratio as a proxy for photochemical age of air masses, substantial formation of secondary organic aerosol (SOA) coatings on rBC particles was observed due to active photochemistry in the afternoon, whereas primary organic aerosol (POA) components were strongly associated with rBC from fresh vehicular emissions in the morning rush hours. There is also evidence that cooking-related organic aerosols were externally mixed from rBC. Positive matrix factorization and elemental analysis illustrate that most of the observed SOA coatings were freshly formed, providing an opportunity to examine SOA coating formation on rBCs near vehicular emissions. Approximately 7-20 wt % of secondary organic and inorganic species were estimated to be internally mixed with rBC on average, implying that rBC is unlikely the major condensation sink of SOA in this study. Comparison of our results to a co-located standard high-resolution time-offlight aerosol mass spectrometer (HR-ToF-AMS) measurement suggests that at least a portion of SOA materials condensed on rBC surfaces were chemically different from oxygenated organic aerosol (OOA) particles that were externally mixed with rBC, although they could both be generated from local photochemistry.

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“…In the atmosphere, fractal soot aggregates age rapidly upon exposure to condensable vapors of sulfuric acid and oxidized organics [37][38][39][40][41][42]. Sufficiently aged soot may undergo significant structural changes, making the aggregates less fractal [16].…”

Section: Soot Aggregatesmentioning

confidence: 99%

The Impact of Sampling Medium and Environment on Particle Morphology

Chen

Enekwizu

et al. 2017

Atmosphere

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Sampling on different substrates is commonly used in laboratory and field studies to investigate the morphology and mixing state of aerosol particles. Our focus was on the transformations that can occur to the collected particles during storage, handling, and analysis. Particle samples were prepared by electrostatic deposition of size-classified sodium chloride, sulfuric acid, and coated soot aerosols on different substrates. The samples were inspected by electron microscopy before and after exposure to various environments. For coated soot, the imaging results were compared against mass-mobility measurements of airborne particles that underwent similar treatments. The extent of sample alteration ranged from negligible to major, depending on the environment, substrate, and particle composition. We discussed the implications of our findings for cases where morphology and the mixing state of particles must be preserved, and cases where particle transformations are desirable.

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Enhanced light absorption by mixed source black and brown carbon particles in UK winter

Cited by 310 publications

References 60 publications

Jury is still out on the radiative forcing by black carbon

Jury is still out on the radiative forcing by black carbon

Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions

The Impact of Sampling Medium and Environment on Particle Morphology

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