Abstract：
Mercury (Hg) emissions from forest fires, especially tropical forests such as the Amazonian forest, were shown to contribute significantly to the atmospheric mercury budget, but new methods are still necessary to improve the traceability and to reduce the great uncertainties related to this emission source. Recent studies have shown that the combustion process can result in Hg stable isotope fractionation that allows tracking coal combustion Hg emissions, as influenced by different factors such as combustion temperature. The main goal of the present study was, therefore, to investigate for the first time the potential of Hg stable isotopes to trace forest fire Hg emissions and pathways. More specifically, small-scale and a large scale prescribed forest fire experiments were conducted in the Brazilian Amazonian forest to study the impact of fire severity on Hg isotopic composition of litter, soil, and ash samples and associated Hg isotope fractionation pathways. In the small-scale experiment, no difference was found in the mercury isotopic composition of the samples collected before and after burning. In contrast, the larger-scale experiment resulted in significant mass dependent fractionation (MDF δ202Hg) in soils and ash suggesting that higher combustion temperature influence Hg isotopic fractionation with the emission of lighter Hg isotopes to the atmosphere and enrichment with heavier Hg in ashes. As for coal combustion, mass independent fractionation was not observed. To our knowledge, these results are the first to highlight the potential of forest fires to cause Hg isotopic fractionation, depending on the fire severity. The results also allowed to establish an isotopic fingerprint for tropical forest fire Hg emissions that corresponds to a mixture of litter and soil Hg isotopic composition (resulting atmospheric δ202Hg, Δ200Hg and Δ199Hg were -1.79 ± 0.24‰, -0.05 ± 0.04‰ and -0.45 ± 0.12‰, respectively).
摘要：
森林火灾中的汞（Hg）排放，尤其是热带森林，如亚马逊森林，被证明对大气汞收支有显著贡献，但是新的方法仍然需要提高可追溯性并减少与该排放源相关的巨大不确定性。最近的研究表明，燃烧过程可以导致汞稳定同位素分馏，从而可以跟踪煤燃烧汞的排放，受燃烧温度等不同因素的影响。本研究的主要目的是,因此,首次研究汞稳定同位素追踪森林火灾汞排放和途径的潜力。更具体地说,在巴西亚马逊森林中进行了小规模和大规模的规定森林火灾实验，以研究火灾严重程度对凋落物汞同位素组成的影响，土壤,以及灰分样品和相关的汞同位素分馏途径。在小规模实验中，燃烧前后收集的样品的汞同位素组成没有差异。相比之下,大规模实验导致土壤和灰分中明显的质量依赖性分馏（MDFδ202Hg），这表明较高的燃烧温度会影响Hg同位素分馏，从而向大气中排放较轻的Hg同位素，并在灰分中富集较重的Hg。至于煤的燃烧，没有观察到质量独立的分馏。据我们所知,这些结果首次突出了森林火灾导致汞同位素分馏的潜力，取决于火灾的严重程度。结果还可以建立热带森林火灾汞排放的同位素指纹，该指纹对应于凋落物和土壤汞同位素组成的混合物（导致大气δ202Hg，Δ200Hg和Δ199Hg为-1.79±0.24‰，-0.05±0.04‰和-0.45±0.12‰，分别)。
