Glenn Chase K, El Hajj Omar, McQueen Zachary, Poland Ryan P, Penland Robert, Roberts Elijah T, Choi Jonathan H, Bai Bin, Shin Nara, Anosike Anita, Kumar Kruthika V, Abdurrahman Muhammad Isa, Liu Pengfei, Amster I Jonathan, Smith Geoffrey D, Flanagan Steven, Callaham Mac A, Loudermilk Eva L, O'Brien Joseph J, Saleh Rawad
School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, Georgia 30602, United States.
Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
ACS EST Air. 2024 Aug 21;1(9):1124-1136. doi: 10.1021/acsestair.4c00089. eCollection 2024 Sep 13.
We investigated the light-absorption properties of brown carbon (BrC) as part of the Georgia Wildland-Fire Simulation Experiment. We constructed fuel beds representative of three ecoregions in the Southeastern U.S. and varied the fuel-bed moisture content to simulate either prescribed fires or drought-induced wildfires. Based on decreasing fire radiative energy normalized by fuel-bed mass loading (FRE), the combustion conditions were grouped into wildfire (Wild), prescribed fire (Rx), and wildfire involving duff ignition (WildDuff). The emitted BrC ranged from weakly absorbing (WildDuff) to moderately absorbing (Rx and Wild) with the imaginary part of the refractive index () values that were well-correlated with FRE. We apportioned the BrC into water-soluble (WSBrC) and water-insoluble (WIBrC). Approximately half of the WSBrC molecules detected using electrospray-ionization mass spectrometry were potential chromophores. Nevertheless, of WSBrC was an order of magnitude smaller than of WIBrC. Furthermore, of WIBrC was well-correlated with FRE while of WSBrC was not, suggesting different formation pathways between WIBrC and WSBrC. Overall, the results signify the importance of combustion conditions in determining BrC light-absorption properties and indicate that variables in wildland fires, such as moisture content and fuel-bed composition, impact BrC light-absorption properties to the extent that they influence combustion conditions.
作为佐治亚州野外火灾模拟实验的一部分，我们研究了棕碳（BrC）的光吸收特性。我们构建了代表美国东南部三个生态区的燃料床，并改变燃料床的含水量以模拟计划火烧或干旱引发的野火。根据以燃料床质量负荷（FRE）归一化的降低的火灾辐射能量，将燃烧条件分为野火（Wild）、计划火烧（Rx）和涉及腐殖质点火的野火（WildDuff）。所排放的BrC范围从弱吸收（WildDuff）到中等吸收（Rx和Wild），其折射率的虚部（）值与FRE高度相关。我们将BrC分为水溶性（WSBrC）和水不溶性（WIBrC）。使用电喷雾电离质谱检测到的WSBrC分子中约有一半是潜在的发色团。然而，WSBrC的 比WIBrC的 小一个数量级。此外，WIBrC的 与FRE高度相关，而WSBrC的 则不然，这表明WIBrC和WSBrC之间的形成途径不同。总体而言，结果表明燃烧条件在决定BrC光吸收特性方面的重要性，并表明野火中的变量，如含水量和燃料床组成，会在影响燃烧条件的程度上影响BrC的光吸收特性。
