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Terms and Definitions

Adapted from: Lehmann, J., and Joseph, S. (2015). Biochar for Environmental Management: An Introduction. In: Biochar for Environmental Management - Science and Technology, 2nd edition. J. Lehmann and S. Joseph (eds.). Routledge.

Biochar: A solid material obtained from thermochemical conversion of biomass in an oxygen-limited environment. Biochar can be used for a range of applications as an agent for soil improvement, improved resource use efficiency, remediation and/or protection against particular environmental pollution and as an avenue for greenhouse gas (GHG) mitigation. In addition, to be recognized as biochar, the material has to pass a number of material property definitions that relate both to its value (e.g., H/Corg ratios relate to the degree of charring and therefore mineralization in soil) and its safety (e.g., heavy metal content).

Hydrochar: The solid product of hydrothermal carbonization (HTC) or liquefaction. It is distinct from biochar due to its production process and properties, and typically has higher H/C ratios and lower aromaticity than biochar as well as little or no fused aromatic ring structures. 

Pyrogenic Carbonaceous Material (PCM): The umbrella term for all materials that were produced by thermochemical conversion and contain some organic C, such as charcoal, biochar, char, black carbon, soot, activated carbon. The term refers to the material and not the C atom.

Char: The material generated by incomplete combustion processes that occur in natural and man-made fires.

Charcoal:  Produced by thermochemical conversion from biomass (mainly but not exclusively wood) for energy generation.

Ash: The operationally defined fraction of biomass or PCM (according to ASTM D1762-84) and typically includes inorganic oxides and carbonates.

Activated carbon: A PCM that has undergone activation, for example by using steam or additions of chemicals.

Black carbon: PCMs dispersed in the environment from wildfires and fossil fuel combustion.

Soot: A secondary PCM and a condensation product. Chars, charcoal, biochars, black carbons (and, to a limited extent, also activated carbon) may contain soot, but soot can also be identified as a separate component resulting from gas condensation processes.

When referring to the C atoms of the PCM, the letter C should be used as in ‘pyrogenic C’ or ‘black C’. A selection of terms referring to C forms in PCM relevant to this publication includes:

  • ‘Black C’ spelled with ‘C’ and not ‘carbon’ refers to the C atom, and not to the material that also contains H, O, N and ash minerals. ‘Black C’ should not be abbreviated to BC as this can be confused with biochar (which is in some publications abbreviated to BC; the acronym BC is therefore not used here).
  • ‘Pyrogenic C’ (abbreviated to PyC after first use) is synonymous with black C. It should be used preferentially to ‘black C’.
  • PyC (or black C) should refer to the (non-inorganic) C atoms that have undergone pyrogenic or thermal transformation, and by this definition only include C present in fused rings, including C on surfaces of fused aromatic C that may also bind to other atoms than C such as C-O/N, non- protonated C and protonated C.
  • ‘Total Organic Carbon’ (abbreviated  TOC) refers to the entire organic C component of any material, and is similarly  defined for PCMs, including  all thermally  altered organic C as well as remaining untransformed organic C. ‘Total inorganic carbon’ (abbreviated TIC) mainly includes carbonate and possibly other compounds such as oxalates.
  • In some cases ‘soot C’ is appropriate to indicate the C atom properties of soot (which  is a secondary PCM as defined above)