Four Decades of Atmospheric Mercury Records at Mt. Everest Reveals Significant Reduction in Anthropogenic Mercury Emissions Over the Past Decade

Abstract

Mercury (Hg) is a highly toxic metal of global concern, with its anthropogenic emissions strictly controlled by the Minamata Convention on Mercury. The effectiveness of this convention is evaluated by global atmospheric Hg monitoring among other indicators. However, it is uncertain to directly link anthropogenic Hg emissions to atmospheric Hg concentrations mainly due to legacy Hg re-emissions. Here, we reconstructed the past atmospheric Hg concentrations and isotope compositions using the annually resolved (1982–2020) leaves of Androsace tapete at Mt. Everest, Tibetan Plateau. Our reconstruction indicates that the atmospheric Hg concentrations increased from the early 1980s to 2002 (3.31 ng m^–3), followed by a large (∼70%) decline until 2020 (0.90 ng m^–3). The declining trend of atmospheric Hg concentrations resembles those observed at North Hemisphere background sites, particularly in Chinese rural areas. Notably, there has been an increasing enrichment of light isotopes in atmospheric Hg over the past decade. Using an isotope mixing model based on δ²⁰²Hg, we show that the atmospheric Hg has declined over the past decade that is mainly driven by reduced anthropogenic emissions. The contributions of the terrestrial legacy re-emissions are rather stable, but their atmospheric fractions increased from ∼44% in 2010 to ∼62% in 2020. Given the importance of legacy Hg, the current strategies should prioritize assessing legacy Hg remobilization.