Chemical and Catalytic Properties of Elemental Carbon

Chang, Shuenn‐Yih; Brodzinsky, R.; Gundel, Lara A.; Novakov, T.

doi:10.1007/978-1-4684-4154-3_11

Cited by 47 publications

(24 citation statements)

References 33 publications

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“…Although the average elemental composition of combustion particles is usually dominated by carbon (typically about 85-95% C, 3-8% O, and 1-3% H by weight in various types of soot particles (Ebert, 1990;Clague et al, 1999;Grieco et al, 2000;Ferry et al, 2002)), an atmospheric soot particle may be regarded as a complex three-dimensional organic polymer with the capability of transferring electrons, rather than merely an amorphous form of elemental carbon (Chang et al, 1982). The relatively low mass fraction of oxygen in soot carbon may be deceiving, since most of it is actually found on the surface in various functional groups, so that the soot particles do not behave as pure graphitic carbon in most atmospheric processes.…”

Section: Introductionmentioning

confidence: 99%

Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

Andreae

Gelencsér²

2006

Atmos. Chem. Phys.

1,789

1,033

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Abstract. Although the definition and measurement techniques for atmospheric "black carbon" ("BC") or "elemental carbon'' ("EC") have long been subjects of scientific controversy, the recent discovery of light-absorbing carbon that is not black ("brown carbon, Cbrown") makes it imperative to reassess and redefine the components that make up light-absorbing carbonaceous matter (LAC) in the atmosphere. Evidence for the atmospheric presence of Cbrown comes from (1) spectral aerosol light absorption measurements near specific combustion sources, (2) observations of spectral properties of water extracts of continental aerosol, (3) laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and (4) indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that brown carbon may severely bias measurements of "BC" and "EC" over vast parts of the troposphere, especially those strongly polluted by biomass burning, where the mass concentration of Cbrown is high relative to that of soot carbon. Chemical measurements to determine "EC" are biased by the refractory nature of Cbrown as well as by complex matrix interferences. Optical measurements of "BC" suffer from a number of problems: (1) many of the presently used instruments introduce a substantial bias into the determination of aerosol light absorption, (2) there is no unique conversion factor between light absorption and "EC" or "BC" concentration in ambient aerosols, and (3) the difference in spectral properties between the different types of LAC, as well as the chemical complexity of Cbrown, lead to several conceptual as well as practical complications. We also suggest that due to the sharply increasing absorption of Cbrown towards the UV, single-wavelength light absorption measurements may not be adequate for the assessment of absorption of solar radiation in the troposphere. We discuss the possible consequences of these effects for our understanding of tropospheric processes, including their influence on UV-irradiance, atmospheric photochemistry and radiative transfer in clouds.

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Section: Introductionmentioning

confidence: 99%

Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

Andreae

Gelencsér²

2006

Atmos. Chem. Phys.

1,789

1,033

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“…Atmospheric "elemental carbon" particles 24 J. C. CHOW ET AL. are commonly considered to be the product of incomplete combustion of carbon-containing fuels in an oxygen-starved environment. Chang et al (1982) de ne EC as ": : : a complex three-dimensional polymer with the capability of transferring electrons. : : : " Seinfeld and Pandis (1998) refer to EC as "soot" that forms when carbon to oxygen ratios during combustion are <1.…”

Section: Introductionmentioning

confidence: 99%

Comparison of IMPROVE and NIOSH Carbon Measurements

Chow

Watson

Crow

et al. 2001

Aerosol Science and Technology

227

344

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Organic carbon (OC) and elemental carbon (EC) are operationally de ned by the analysis methods, and different methods give in different results. The IMPROVE (Interagency Monitoring of Protected Visual Environments) and NIOSH (National Institute of Occupational Safety and Health) thermal evolution protocols present different operational de nitions. These protocols are applied to 60 ambient and source samples from different environments using the same instrument to quantify differences in implemented protocols on the same instrument. The protocols are equivalent for total carbon sampled on quartz-ber lters. NIOSH EC was typically less than half of IMPROVE EC. The primary difference is the allocation of carbon evolving at the NIOSH 850 ± C temperature in a helium atmosphere to the OC rather than EC fraction. Increasing light transmission and re ectance during this temperature step indicate that this fraction should be classi ed as EC. When this portion of NIOSH OC is added to NIOSH EC, the IMPROVE and NIOSH analyses are in good agreement. The most probable explanation is that mineral oxides in the complex particle mixture on the lter are supplying oxygen to neighboring carbon particles at this high temperature. This has been demonstrated by the principle of the thermal manganese oxidation method that is also commonly used to distinguish OC from EC. For both methods, the optical pyrolysis adjustment to the EC fractions was always higher for transmittance than for re ectance. This is a secondary cause of differences between the two methods, with transmittance resulting in a lower EC loading than re ectance. The difference was most pronounced for very black lters on which neither re ectance nor transmittance accurately detected further blackening due to pyrolysis.

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“…Subsequently, they absorb organic vapors when the combustion products cool down and frequently accumulate significant mass fractions of organic compounds. Thus, soot substances consist in general of a mixture of EC, OC, and other elements such as oxygen, nitrogen, and hydrogen incorporated in its graphitic structure (Chang, Brodzinsky, and Gundel, 1982). The EC found in atmospheric particles is not usually present in the large-size particles of highly structured pure graphite but tends to form three-dimensional arrays of carbon with small fractions of other elements, containing a high number of crystallites having sizes of 2-3 nm, all consisting of several carbon layers presenting the hexagonal structure of graphite.…”

Section: Anthropogenic Aerosols From Fossil Fuel Combustion and Carbomentioning

confidence: 99%