Department of Mechanical Engineering, The University of Wyoming, Laramie, WY, USA.
Department of Mechanical Engineering, The University of Wyoming, Laramie, WY, USA.
Sci Total Environ. 2022 Nov 25;849:157610. doi: 10.1016/j.scitotenv.2022.157610. Epub 2022 Jul 28.
Pyrogenic carbon (PyC) is an important component of wildfire chars and engineered biochars due to its potential environmental longevity, the most environmentally stable fraction of which is called stable polycyclic aromatic carbon (SPAC) and is projected to persist in global environments for >1000 yr. Rigorous characterization of SPAC, whether formed in wildfires or engineered, is essential for accurate global carbon cycle models. However, the quantification of SPAC remains challenging and methods for its direct characterization are often inaccessible and/or highly specialized. Additionally, these methods often rely on SPAC formation measured in laboratory biochars produced in inert environments, which have been shown to correlate poorly with wildfire chars and/or engineered biochars manufactured in oxidative environments. The present study investigated the relationship between SPAC formation and physicochemical metrics - mass loss and molar H:C and O:C ratios - that capture the influences of multiple formation variables, including gas environment temperature, O availability, and pyrolysis duration, and negates the need for these variables to be directly measured. SPAC content is measured in this study using hydrogen pyrolysis (HyPy), which is an established accurate method for characterizing that most environmentally stable PyC fraction. Results show that SPAC formation and elemental ratios correlate linearly with increased mass loss, which is reflective of increased pyrolysis severity. The relationship between these char characteristics allows for SPAC prediction based on measurement of mass loss during char formation, as well as the standardized elemental analysis method. In this study, wildfire chars exhibited relatively low SPAC contents of <30 wt% on a dry, ash-free basis, indicating that a significant fraction of PyC formed in these chars remains labile or semi-labile, while engineered biochars had a range of SPAC contents up to approximately 75 wt%. The predictive SPAC models developed in this work can improve global carbon accounting models.
热解碳（PyC）是野火炭和工程生物炭的重要组成部分，因为其具有潜在的环境长寿命，其中最稳定的环境部分称为稳定多环芳烃碳（SPAC），预计在全球环境中存在超过 1000 年。对 SPAC 的严格表征，无论是在野火中还是在工程中形成的，对于准确的全球碳循环模型都是必不可少的。然而，SPAC 的定量仍然具有挑战性，其直接表征的方法通常无法获得和/或高度专业化。此外，这些方法通常依赖于在惰性环境中产生的实验室生物炭中测量的 SPAC 形成，这已被证明与氧化环境中制造的野火炭和/或工程生物炭相关性较差。本研究调查了 SPAC 形成与物理化学指标之间的关系 - 质量损失和摩尔 H:C 和 O:C 比 - 这些指标捕捉了多种形成变量的影响，包括气体环境温度、O 可用性和热解持续时间，并且不需要直接测量这些变量。本研究使用氢热解（HyPy）测量 SPAC 含量，这是一种用于表征最稳定的 PyC 部分的成熟准确方法。结果表明，SPAC 的形成和元素比与增加的质量损失线性相关，这反映了增加的热解严重程度。这些炭特征之间的关系允许基于在炭形成过程中测量的质量损失以及标准化的元素分析方法来预测 SPAC。在本研究中，野火炭的 SPAC 含量相对较低，<30wt%，在干燥、无灰基础上，这表明在这些炭中形成的 PyC 的很大一部分仍然不稳定或半不稳定，而工程生物炭的 SPAC 含量范围高达约 75wt%。本工作中开发的预测 SPAC 模型可以改进全球碳核算模型。
