Stable polycyclic aromatic carbon (SPAC) formation in wildfire chars and engineered biochars
Stable polycyclic aromatic carbon (SPAC) formation in wildfire chars and engineered biochars
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野火炭和工程生物炭中稳定的多环芳香碳（SPAC）形成
DOI：
10.1016/j.scitotenv.2022.157610
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发表时间：
2022
影响因子：
9.8
通讯作者：
Belmont, Erica
中科院分区：
文献类型：
--
作者：
Howell, Alexandra;Helmkamp, Sophia;Belmont, Erica
热解碳（PyC）是野火炭和工程生物炭的重要组成部分，具有潜在的环境寿命，其中最稳定的部分被称为稳定多环芳烃碳（SPAC），预计在全球环境中持续存在超过1000年。SPAC的严格表征，无论是在野火中形成的还是工程设计的，对于精确的全球碳循环模型至关重要。然而，SPAC的量化仍然具有挑战性，其直接表征的方法往往是不可访问的和/或高度专业化的。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，其已显示与野火炭和/或在氧化环境中制造的工程化生物炭的相关性很差。本研究调查了SPAC形成和物理化学指标之间的关系-质量损失和摩尔H：C和O：C比-捕获多个形成变量的影响，包括气体环境温度，O2的可用性，和热解持续时间，并否定这些变量的需要直接测量。在这项研究中，使用氢热解（HyPy）测量SPAC含量，这是一种用于表征最环境稳定的PyC馏分的已建立的准确方法。结果表明，SPAC的形成和元素的比例与增加的质量损失，这是增加的热解严重性的反映线性相关。这些焦炭特性之间的关系允许SPAC预测的基础上测量的质量损失在焦炭的形成，以及标准化的元素分析方法。在这项研究中，野火炭表现出相对较低的SPAC含量，在干燥、无灰的基础上<30重量%，表明在这些炭中形成的PyC的显著部分保持不稳定或半不稳定，而工程化生物炭具有高达约75重量%的SPAC含量范围。本研究所开发的SPAC预测模型可以改进全球碳核算模型。
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, O2availability, 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.