Biogeochemistry & Environmental Quality Research Group, Clemson University, Georgetown, South Carolina 29442, United States.
Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
Environ Sci Technol. 2022 Sep 6;56(17):12678-12687. doi: 10.1021/acs.est.2c00426. Epub 2022 Aug 10.
High-intensity wildfires alter the chemical composition of organic matter, which is expected to be distinctly different from low-intensity prescribed fires. Herein, we used pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), in conjunction with solid-state C nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy, to assess chemical alterations from three wildfires and a long-term frequent prescribed fire site. Our results showed that black ash formed under moderate intensity burns contained less aromatic (ArH), polyaromatic hydrocarbon (PAH), and nitrogen-containing compounds (Ntg) but more lignin (LgC) and phenol compounds (PhC), compared to white ash formed under high intensity burns. Both C NMR and FT-IR confirmed a higher relative percentage of carboxyl carbon in white ash, indicating the potential for higher water solubility and more mobile carbon, relative to black ash. Compared to wildfires, ash from low-intensity prescribed fire contained less ArH, PAH, and Ntg and more LgC and PhC. Controlled laboratory burning trials indicated that organic matter alteration was sensitive to the burn temperature, but not related to the fuel type (pine vs fir) nor oxygen absence/presence at high burn temperatures. This study concludes that higher burn temperatures resulted in higher (poly)aromatic carbon/nitrogen and lower lignin/phenol compounds.
高强度野火会改变有机质的化学组成，预计与低强度有控制火烧相比有明显差异。在此，我们采用热裂解气相色谱/质谱联用（Py-GC/MS），结合固态 C 核磁共振（NMR）和傅里叶变换红外（FT-IR）光谱，评估了三种野火和一个长期频繁有控制火烧点的化学变化。结果表明，与高强度火烧形成的白灰相比，中强度火烧形成的黑灰中含有的芳族（ArH）、多环芳烃（PAH）和含氮化合物（Ntg）较少，但木质素（LgC）和酚类化合物（PhC）较多。C NMR 和 FT-IR 均证实白灰中羧基碳的相对百分比较高，表明其水溶性更高，移动性更强，相对黑灰而言。与野火相比，低强度有控制火烧形成的灰中 ArH、PAH 和 Ntg 较少，LgC 和 PhC 较多。受控实验室燃烧试验表明，有机质的变化对燃烧温度敏感，但与燃料类型（松树与冷杉）或高温下的缺氧/有氧无关。本研究得出结论，较高的燃烧温度会导致较高的（多）芳族碳/氮和较低的木质素/酚类化合物。
