Evidence for multi-decadal fuel buildup in a large California wildfire from smoke radiocarbon measurements
Evidence for multi-decadal fuel buildup in a large California wildfire from smoke radiocarbon measurements
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DOI：
10.1088/1748-9326/aced17
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发表时间：
2023-08
影响因子：
6.7
通讯作者：
A. Odwuor;C. Yañez;Y. Chen;F. Hopkins;A. Moreno;X. Xu;C. Czimczik;J. Randerson
中科院分区：
文献类型：
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作者：
A. Odwuor;C. Yañez;Y. Chen;F. Hopkins;A. Moreno;X. Xu;C. Czimczik;J. Randerson
近几十年来，加利福尼亚州内华达山脉的年燃烧面积显著增加。火灾活动的增加促使人们需要了解历史上的森林管理做法是如何影响燃料组成和排放的。在这里，我们研究了KNP综合火灾排放的颗粒物(PM)的总碳(TC)浓度和放射性碳丰度(Δ14C)，这场火灾发生在加利福尼亚州2021年的野火季节，影响了内华达山脉南部的几个巨型红杉树林。在26小时的采样期内，我们使用地面移动实验室测量了空气中细颗粒物(PM2.5)的浓度，以及干空气中一氧化碳(CO)和甲烷(CH4)的摩尔分数。我们还采集了PM2.5中的过滤样品，用于TC浓度和Δ14C的分析。PM2.5、CO和CH4时间序列之间的高度相关性证实了我们的PM2.5测量捕捉到了野火排放的可变性。利用基林图方法，我们确定了PM2.514C的平均值为111.6±7.7‰(n=12)，相对于2021年北半球大气中的二氧化碳(−3.2±1.4‰)，PM2.514C是相当丰富的。结合这些Δ14C数据和稳态单箱生态系统模型，我们估计了在KNP复合体火灾中燃烧的燃料的平均年龄为40年，范围为29-57年。这些结果为几十年来积累的木质生物质、较大直径的细燃料和粗糙的木质碎片产生的排放提供了证据。这与独立的野外观测一致，即高火灾强度导致了大片巨杉的死亡。随着加州计划在未来十年扩大使用规定的火灾以减轻野火影响，我们的测量方法有可能提供对燃料处理计划有效性的地区综合评估。
In recent decades, there has been a significant increase in annual area burned in California’s Sierra Nevada mountains. This rise in fire activity has prompted the need to understand how historical forest management practices affect fuel composition and emissions. Here we examined the total carbon (TC) concentration and radiocarbon abundance (Δ14C) of particulate matter (PM) emitted by the KNP Complex Fire, which occurred during California’s 2021 wildfire season and affected several groves of giant sequoia trees in the southern Sierra Nevada. During a 26 h sampling period, we measured concentrations of fine airborne PM (PM2.5), as well as dry air mole fractions of carbon monoxide (CO) and methane (CH4), using a ground-based mobile laboratory. We also collected filter samples of PM2.5 for analysis of TC concentration and Δ14C. High correlation among PM2.5, CO, and CH4 time series confirmed that our PM2.5 measurements captured variability in wildfire emissions. Using a Keeling plot approach, we determined that the mean Δ14C of PM2.5 was 111.6 ± 7.7‰ (n = 12), which was considerably enriched relative to atmospheric carbon dioxide in the northern hemisphere in 2021 (−3.2 ± 1.4‰). Combining these Δ14C data with a steady-state one-box ecosystem model, we estimated that the mean age of fuels combusted in the KNP Complex Fire was 40 years, with a range of 29–57 years. These results provide evidence for emissions originating from woody biomass, larger-diameter fine fuels, and coarse woody debris that have accumulated over multiple decades. This is consistent with independent field observations that indicate high fire intensity contributed to widespread giant sequoia mortality. With the expanded use of prescribed fires planned over the next decade in California to mitigate wildfire impacts, our measurement approach has the potential to provide regionally-integrated estimates of the effectiveness of fuel treatment programs.