Analysis of Organic matter from cloud particles

Bank, Shelton; Castillo, Raymond A.

doi:10.1029/gl014i003p00210

Cited by 17 publications

(6 citation statements)

References 6 publications

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“…2). Tannin/lignin compounds which have similar properties were identified in precipitation (Likens et al, 1983), whereas in cloud water insoluble black particles with the distinguishing infrared absorption bands for both protein and cellulose, and brown particles with the imprint of decomposed proteins have been observed (Bank and Castillo, 1987).…”

Section: Introductionmentioning

confidence: 95%

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

Andreae¹,

Gelencsér²

2006

Preprint

469

640

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Abstract. Although the definition and measurement methods of atmospheric ''black carbon'' (''BC'') 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 directly from aerosol absorption measurements near specific combustion sources, from observations of spectral properties of water extracts of continental aerosol, from laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that these species may severely bias measurements of ''BC'' and ''EC'' over vast parts of the troposphere, where mass concentration of Cbrown is high relative to that of combustion soot. We also imply that due to the strongly skewed 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. The possible consequences of these effects on our understanding of tropospheric processes are discussed.

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Section: Introductionmentioning

confidence: 95%

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

Andreae¹,

Gelencsér²

2006

Preprint

469

640

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show abstract

Section: Introductionmentioning

confidence: 99%

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

Andreae

Gelencsér²

2006

Atmos. Chem. Phys.

1,791

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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“…One of the major contributing factors to the disagreement has been recognized as charring formation from the organic constituents (2,4). The OC fraction consists of a wide variety of molecular forms, ranging from simple alkanes to insoluble polymers such as cellulose (8)(9)(10). Some organic species in ambient aerosols produce pyrolytically generated EC (PEC) (i.e., char) during thermal analysis (2,11,12).…”

Section: Introductionmentioning

confidence: 99%

Charring Characteristics of Atmospheric Organic Particulate Matter in Thermal Analysis

Wang

Yang

2002

Environ. Sci. Technol.

203

141

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The charring of organic materials during carbon analysis bythermal methods makes it difficult to differentiate elemental carbon (EC) from organic carbon (OC). Failure to correct for charring results in the overestimation of EC and the underestimation of OC. The charring characteristics andthermal behaviors of aerosol OC are studied by subjecting hexane and water extracts of ambient aerosols to various analysis conditions. The complete evolution of water-soluble organic carbon (WSOC) aerosol materials is found to require a temperature as high as 850 degrees C and the presence of oxygen. EC would be oxidized under these thermal conditions as well. As a result, thermal methods relying only on temperature for the differentiation of EC and OC would give unreliable OC and EC concentrations. Our investigation also reveals that WSOC accounts for a large fraction (13-66%) of charring, while hexane extractable organic compounds produce little charring. The extent of charring from WSOC, defined as the ratio between pyrolytically generated EC to the total WSOC, is found to increase with the WSOC loading in each analysis when the loadings are below a certain value. This ratio remains constant when the loadings are above this value. This may account for the high variability in the extent of charring among aerosol samples from different locations as well as among samples from a single location collected at different times. Charring is reduced if the residence time at each temperature step in a helium atmosphere is sufficiently long to allow for maximum C evolution at each step. Charring is also influenced by the presence of inorganic constituents such as ammonium bisulfate. For the few tested organic materials, it is observed that ammonium bisulfate enhances the charring of starch and cellulose but reduces the charring of levoglucosan.

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Analysis of Organic matter from cloud particles

Cited by 17 publications

References 6 publications

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

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

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

Charring Characteristics of Atmospheric Organic Particulate Matter in Thermal Analysis

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