ABSTRACT

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 (Cr₂O₇) 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 Cr₂O₇ method. Therefore, we proposed an improved Cr₂O₇ method by increasing acidic K₂Cr₂O₇ 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 Cr₂O₇ method to natural soil was confirmed with 99 to 103% certainty (recovery rate).

摘要

热解碳（PyC）或黑碳（BC）是草原和森林火灾和化石燃料燃烧的残留物，在土壤中的碳储存和污染物吸附中起着重要作用。要了解其在土壤中的作用，有必要准确评估 PyC 分数。然而，土壤是无机和有机物质的复杂混合物，通常含有腐殖质，即非 PyC 有机物质，其浓度比 PyC 高一到两个数量级。这导致难以确定土壤中的 PyC 含量；因此，针对不同的研究目的提出了各种定量方法。在本研究中，两种广泛使用的 375°C 化学热氧化方法 (CTO-375) 和酸性重铬酸盐氧化 (Cr ₂ O ₇) 方法在使用模型土壤确定土壤 PyC 含量的适用性方面进行了重新考虑。CTO-375 方法更简单，但建议量化的 PyC 是非 PyC 有机物的燃烧残留物。相比之下，29% 到 40% 的 PyC 含量通过 Cr ₂ O ₇方法被确定为非 PyC 有机物。因此，我们提出了一种改进的 Cr ₂ O ₇方法，通过将酸性 K ₂ Cr ₂ O ₇浓度提高三倍以提高定量精度：虽然耗时，但它导致对 PyC 含量的最低高估，即从非 PyC 有机物。改进型Cr ₂的应用O ₇方法对天然土壤的确定性（回收率）为 99% 至 103%。