Black carbon reference materials - Background and navigation

FAQ

Definitions

This website would mainly serves the soil and sediment community studying black carbon. In this context, some clarifications are given regarding the use of the term Black carbon.

Black carbon (BC): BC in soils and sediments is defined as a carbonaceous substance of pyrogenic origin, which is resistant to thermal or chemical degradation under the conditions applied in the methods used in the comparative study. According to estimates found in literature, >80 % of BC produced ends up in the soil, where it can reside for hundreds to thousands of years, being relatively resistant to biological and chemical breakdown (Forbes et al., 2006, Preston and Schmidt, 2006). Black carbon therefore represents a pool of C with a long residence time – in essence BC is a carbon sink. For soils and sediments, the light-absorbing characteristics of the substance are not part of our definition of black carbon. What is important is the chemical and thermal stability (and hence longevity) of BC either due to chemical recalcitrance that is evident from its aromatic structure or physical protection due to its surface functionality and binding with minerals and other organic compounds (Brodowski et al., 2005; Forbes et al., 2006).

Elemental carbon (EC): This term is used in atmospheric sciences, and is in most cases referring to the fraction of carbon that is oxidised in combustion analysis above a certain temperature threshold, and only in the presence of an oxygen-containing atmosphere (Andreae & Gelencsér, 2006). The term EC is sometimes used interchangeably with BC.

References:

Andreae, M.O., Gelencsér, A. 2006. Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols. Atmospheric Chemistry and Physics 6, 3131-3148.

Brodowski S., Amelung, W., Haumaier, L., Abetz, C., Zech, W. 2005. Morphological and chemical properties of black carbon in physical soil fractions as revealed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Geoderma 128, 116-129.

Forbes, M.S., Raison, R.J., Skjemstad, J.O. 2006. Formation, transformation and transport of black carbon (charcoal) in terrestrial and aquatic ecosystems. Science of the Total Environment 370, 190-206.

Preston, C.M., Schmidt, M.W.I. 2006. Black (pyrogenic) carbon: a synthesis of current knowledge and uncertainties with special consideration of boreal regions. Biogeoscience 3, 397-420.

The term black carbon (BC) is a general one applied to various carbonaceous products of incomplete combustion and includes chars, charcoals and soots. BC is ubiquitous in the environment, including in aerosols, sediments and soils. Current intercomparison efforts have made clear the need for a suite of widely available and representative BC benchmark materials. To address this need, an international steering committee was formed during the 1999 Geochemical Society meeting (Goldschmidt Conference). This committee was charged with developing representative and accessible BC reference materials for the environmental sciences community. In May 2000 this committee issued preliminary recommendations for BC materials spanning the combustion continuum (Reference Materials). Recommendations include i) five BC-containing environmental matrices for which BC quantification is often sought, namely aerosol, two soils, marine sediment and dissolved organic matter, ii) three laboratory-produced BC-rich materials, namely soot, wood charcoal and grass char, and iii) four potentially interfering materials, creating BC during analysis (melanoidin, shale, two coals). This collection had to be chosen to balance a number of competing demands. Materials must be: 1) generally available, 2) homogeneous, 3) stable over a longer period of time, 4) inexpensive to obtain, and 5) represent natural samples. After issuing preliminary recommendations via this web site, the BC steering committee actively solicited input from scientists and used this information to make a final set of recommendations of BC benchmark materials that were analyzed in a comparative study. A summary of these recommendations was published in EOS, the weekly journal published by the American Geophysical Union (www.agu.org) "Final Recommendations for Reference Materials in Black Carbon Analysis".

The comparative study was brought to a close with the publication of a manuscript in Global Biogeochemical Cycles (Comparision of quantification methods to measure fire-derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment, and the atmosphere. Global Biogeochemical Cycles, 21, GB3016, doi:10.1029/2006GB002914).

A short report on the latest symposium held on black carbon research in soil, sediment and the atmosphere at the European Geoscience Union meeting in Vienna (18-19 April 2007), as well as summary of the comparative study conclusions, can be found here (PDF).

People