Quantification methods of pyrogenic carbon in soil with soil as a complex matrix: comparing the CTO-375 and Cr2O7 methods

Pyrogenic carbon (PyC) or black carbon (BC), the residue of grassland and forest fires and fossil fuel combustion, plays an important role in carbon storage and pollutant adsorption in soil. To understand its roles in soil, it is necessary to accurately assess the PyC fraction. Soil is, however, a c...

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Bibliographic Details
Published in:Soil science and plant nutrition (Tokyo) 2021-07, Vol.67 (4), p.380-388
Main Authors: Murano, Hirotatsu, Liu, Guanchu, Wang, Zhengyang, Tanihira, Yuki, Asahi, Toshiya, Isoi, Toshiyuki
Format: Article
Language:English
Subjects:
Black carbon
Carbon
Carbon sequestration
Combustion
CTO-375 method
Forest fires
Fossil fuels
Fuel combustion
Grasslands
Humic acids
Humic substances
method
Methods
Organic matter
Oxidation
Pollutants
Potassium dichromate
Pyrogenic carbon
Quantification method
Residues
Soil adsorption
Soil pollution
Soils
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Summary:Pyrogenic carbon (PyC) or black carbon (BC), the residue of grassland and forest fires and fossil fuel combustion, plays an important role in carbon storage and pollutant adsorption in soil. To understand its roles in soil, it is necessary to accurately assess the PyC fraction. Soil is, however, a complex mixture of inorganic and organic matter, usually containing humic substances, i.e., non-PyC organic matter, in concentrations one to two orders of magnitude higher than PyC. This engenders difficulty in determining the PyC content in soils; thus, various quantitative methods have been proposed for different research purposes. In this study, the two widely used methods of chemo-thermal oxidation at 375°C (CTO-375) and acid dichromate oxidation (Cr 2 O 7 ) method were reconsidered in terms of the suitability for determining the PyC content of soil by using model soil. The CTO-375 method was simpler, but the quantified PyC was suggested to be the combustion residue of non-PyC organic matter. By contrast, 29 to 40% of PyC content was determined as non-PyC organic matter by the Cr 2 O 7 method. Therefore, we proposed an improved Cr 2 O 7 method by increasing acidic K 2 Cr 2 O 7 concentration threefold for quantification accuracy: although time-consuming, it resulted in the lowest overestimation on the PyC content, that is, 16 to 23% from non-PyC organic matter. The application of the improved Cr 2 O 7 method to natural soil was confirmed with 99 to 103% certainty (recovery rate).
ISSN:0038-0768
1747-0765
DOI:10.1080/00380768.2021.1925960