Department of Chemistry, University of Michigan, Ann Arbor, MI 48109.
Division of Atmospheric Science, Desert Research Institute, Reno, NV 89523.
Proc Natl Acad Sci U S A. 2019 Jul 16;116(29):14479-14484. doi: 10.1073/pnas.1900613116. Epub 2019 Jun 28.
Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. However, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic. Measured bromine atom levels reached 14 parts per trillion (ppt, pmol mol; 4.2 × 10 atoms per cm) and were up to 3-10 times higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.
溴原子在大气反应性卤族化学中起着核心作用，消耗臭氧和元素汞，从而促进有毒汞的沉积，特别是在北极近地表对流层。然而，由于缺乏足够灵敏度的分析能力来进行环境测量，目前还缺乏对溴原子的直接测量。在这里，我们展示了在北极春季进行的直接大气溴原子测量。测量到的溴原子水平达到了 14 个 ppt（pmol/mol；4.2×10 个原子/cm），比以前使用间接测量而不考虑分子溴的关键作用的估计值高出 3-10 倍。所观测到的臭氧和元素汞消耗率可以通过测量的溴原子定量解释，从而为高度不确定的汞化学提供了现场验证。在完全耗尽臭氧后，由分子溴和氮氧化物的光化学积雪排放维持的溴浓度升高，导致大气汞的持续消耗。这项研究在定量约束极地大气中的溴化学方面取得了突破，这种化学将快速变化的表面与污染物命运联系起来。
