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Title: Near Infrared Spectroscopie Examination of Charred Pine Wood, Bark, Cellulose and Lignin: Implications For the Quantitative Determination of Charcoal In Soils by NIRS

Author
item Reeves Iii, James
item McCarty, Gregory
item RUTHERFORD, D - USGS
item WERSHAW, R - USGS

Submitted to: Near Infrared Spectroscopy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2007
Publication Date: 9/18/2007
Citation: Reeves III, J.B., Mccarty, G.W., Rutherford, D.W., Wershaw, R.L. 2007. Near Infrared Spectroscopie Examination of Charred Pine Wood, Bark, Cellulose and Lignin: Implications For the Quantitative Determination of Charcoal In Soils by NIRS. Near Infrared Spectroscopy Journal. 15:307-315.

Interpretive Summary: The composition and amount of carbon (C) in soils has become of intense interest both because of its importance to soil structure and fertility and for soil’s potential to sequester atmospheric carbon dioxide; thus helping to reduce global warming by removing carbon dioxide from the atmosphere. Carbon in the form of char or charcoal resulting from fires can comprise a significant fraction of soil C in areas where burns are frequent and has a much longer residence time than C from plant residues, etc. Unfortunately, there is no accepted or easy method for determining charcoal in soils. Near-infrared (NIR) spectroscopy (NIRS) uses light beyond the range of human sight to determine the composition of organic containing materials by relating the absorbed light to composition. The objective of this research was to investigate the effect of charring on NIR spectra of materials likely to be present in forest fires in order to determine the feasibility of determining charcoal C in soils by NIRS. Four materials (cellulose, lignin, pine bark and pine wood) and char from these materials created by charring for various durations (1 to 168 H) and at various temperatures (200 to 450 C) were studied. Near-infrared spectra and measures of acidity (total acids, carboxylic acids, lactones and phenols as determined by titration) were available for 56 different samples (Not all samples charred at all temperatures/durations). Results showed spectral changes that varied with the material, temperature and duration of charring. Examination of spectra and correlation plots indicated that changes in the constituents of the materials in questions, such as loss of OH groups in carbohydrates rather, than direct determination of typical products produced by charring such as carboxylic acids, lactones and phenols are the basis for the spectral changes. Finally, while the spectral changes resulting from charring appeared to be relatively unique to each material, results with NIRS indicated that there is a sufficient commonality in the changes to be able to quantitatively determine charcoal in soils by way of the chemical changes caused by charring.

Technical Abstract: The objective of this research was to investigate the effect of charring on near-infrared spectra of materials likely to be present in forest fires in order to determine the feasibility of determining charred C in soils. Four materials (cellulose, lignin, pine bark and pine wood) and char from these materials created by charring for various durations (1 to 168 H) and at various temperatures (200 to 450 C) were studied. Near-infrared spectra and measures of acidity (total acids, carboxylic acids, lactones and phenols as determined by titration) were available for 56 different samples (Not all samples charred at all temperatures/durations). Results showed spectral changes that varied with the material, temperature and duration of charring. Examination of spectra and correlation plots indicated that changes in the constituents of the materials in questions, such as loss of OH groups in carbohydrates rather, than direct determination of typical products produced by charring such as carboxylic acids, lactones and phenols are the basis for the spectral changes. Finally, while the spectral changes resulting from charring appeared to be relatively unique to each material, PLS calibrations for total acids, carboxylic acids, lactones and phenols were successfully created (min. R2 of .931 for lactones) indicating that there is a sufficient commonality in the changes to develop calibrations without the need for unique calibrations for each specific case.