Reflectance as an indicator of biochar permanence

The data submitted was used to write an article: Mastalerz, M., Drobniak, A., Liu, B., Pauer, P., Reflectance as an indicator of biochar permanence. Funding acknowledgments: Agnieszka Drobniak funding comes from the Polish National Agency for Academic Exchange within the Polish Returns Programme (BPN/PPO/2021/1/00005/DEC/1), the National Science Center, Poland (2022/01/1/ST10/00024), and the research activities co-financed by the funds granted under the Research Excellence Initiative of the University of Silesia in Katowice, Poland. Article Abstract: Biochar, a carbon-rich product of biomass pyrolysis, holds considerable potential for carbon sequestration, soil amendment, and environmental remediation. Its effective application, however, hinges on understanding biochar permanence and on employing robust methodologies to reliably assess its stability and reactivity. This study investigates the relationship between reflectance and the chemical composition (elemental ratios and organic functional groups) of biochar produced from sycamore wood, wheat straw, and peanut shells across well-controlled pyrolysis temperatures ranging from 300 °C to 700 °C, aiming to assess the potential of biochar reflectance as an indicator of biochar permanence. The results demonstrate strong correlations between biochar reflectance and H/C and O/C molar ratios and show that the reflectance increases systematically with pyrolysis temperature. A strong correlation between the elemental O/C ratio and the FTIR-derived ratio of oxygenated groups to aromatic carbon across different pyrolysis temperatures provides additional valuable insights for predicting biochar stability. The findings point to pyrolysis temperature as the dominant factor influencing biochar longevity and reinforce the suggestion that biochars with reflectance values above 2.0 % are non-reactive and are expected to be stable in the environment for a very long time. The results highlight biochar reflectance as a rapid and effective proxy for predicting biochar permanence, supporting its utility in carbon sequestration and environmental management.