Air–soil exchange of elemental mercury vapor (Hg⁰) is an important component in the budget of the global mercury cycle. However, its mechanistic detail is poorly understood. In this study, stable Hg isotopes in air, soil, and pore gases are characterized in a subtropical evergreen forest to understand the mechanical features of the air–soil Hg⁰ exchange. Strong Hg^II reduction in soil releases Hg⁰ to pore gas during spring–autumn but diminishes in winter, limiting the evasion in cold seasons. Δ¹⁹⁹Hg in air modified by the Hg⁰ efflux during flux chamber measurement exhibit seasonality, from −0.33 ± 0.05‰ in summer to −0.08 ± 0.05‰ in winter. The observed seasonal variation is caused by a strong pore-gas driven soil efflux caused by photoreduction in summer, which weakens significantly in winter. The annual Hg⁰ gross deposition is 42 ± 33 μg m^–2 yr^–1, and the corresponding Hg⁰ evasion from the forest floor is 50 ± 41 μg m^–2 yr^–1. The results of this study, although still with uncertainty, offer new insights into the complexity of the air-surface exchange of Hg⁰ over the forest land for model implementation in future global assessments.

中文翻译：

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汞同位素对亚热带森林地面大气汞沉积和遗留再排放的量化

元素汞蒸气 (Hg ⁰ ) 的空气-土壤交换是全球汞循环预算中的一个重要组成部分。然而，人们对其机械细节知之甚少。在这项研究中，空气、土壤和孔隙气体中的稳定 Hg 同位素在亚热带常绿森林中被表征，以了解空气 - 土壤 Hg ⁰交换的机械特征。土壤中Hg ^{II 的}强烈减少在春秋期间将 Hg ⁰释放到孔隙气体中，但在冬季减少，限制了寒冷季节的逃逸。Δ ¹⁹⁹ Hg 空气中的 Hg ⁰通量室测量期间的外排具有季节性，从夏季的 -0.33 ± 0.05‰ 到冬季的 -0.08 ± 0.05‰。观察到的季节性变化是由夏季光还原引起的强烈孔隙气体驱动的土壤流出引起的，冬季显着减弱。年 Hg ⁰总沉积量为 42 ± 33 μg m ^–2 yr ^–1，相应的从森林地面逃逸的Hg ⁰为 50 ± 41 μg m ^–2 yr ^–1。尽管仍存在不确定性，但这项研究的结果提供了新的见解，以了解林地空气-地表交换 Hg ⁰的复杂性，以便在未来的全球评估中实施模型。