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Molecular heterogeneity in pyrogenic dissolved organic matter from a thermal series of oak and grass chars

Author(s): Wozniak, Andrew S; Goranov, Aleksandr I; Mitra, Siddhartha; Bostick, Kyle W; Zimmerman, Andrew R; et al

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Abstract: Pyrogenic organic matter (Py-OM), generated via the incomplete combustion of biomass, is well studied due to the presence of slow-cycling, condensed aromatic compounds (ConAC) known to sequester in soils and sediments. Recently, dissolved Py-OM (Py-DOM) has received interest, due to its higher mobility and potential to be transferred through watersheds to aquatic systems. Py-DOM quantities, molecular identities and importance to global carbon budgets and cycles are only beginning to be understood. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) analyses were performed on Py-DOM isolated from oak and grass biochars produced over a range of temperatures (250–650 °C), and the data are compared to complementary 1H NMR spectroscopic and benzenepolycarboxylic acid biomarker (BPCAs) analyses. Py-DOM is revealed to be a heterogeneous mixture of compounds ranging in relative aromaticity and oxygenation. FTICR-MS analyses demonstrate a decrease in Py-DOM relative oxygen content and a concurrent increase in aliphatic character and heteroatomic (N, Cl) content. 1H NMR and BPCAs analyses detail low O/C dissolved ConAC not observed by FTICR-MS, demonstrating the necessity for a multiple proxy approach to Py-DOM characterization. Heterogeneous Py-DOM is explained as resulting from pyrolysis-initiated and radical-mediated functional group cleavage, aromatic condensation and aromatic ring-opening reactions. Oak biomass progresses faster along a char maturity continuum for a given pyrolysis temperature, perhaps due to its greater lignin content or radical quenching by grass cuticular material. Biomass species and pyrolysis temperature likely result in different Py-DOM compositions and fates and must be considered when evaluating the impacts of wildfires and biochar applications.
Publication Date: Oct-2020
Electronic Publication Date: 24-Jun-2020
Citation: Wozniak, Andrew S., Aleksandar I. Goranov, Siddhartha Mitra, Kyle W. Bostick, Andrew R. Zimmerman, Danielle R. Schlesinger, Satish C.B. Myneni, and Patrick G. Hatcher. "Molecular heterogeneity in pyrogenic dissolved organic matter from a thermal series of oak and grass chars." Organic Geochemistry 148 (2020): 104065. doi:10.1016/j.orggeochem.2020.104065.
DOI: doi:10.1016/j.orggeochem.2020.104065
ISSN: 0146-6380
Type of Material: Journal Article
Journal/Proceeding Title: Organic Geochemistry
Version: Author's manuscript

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