Forest Mercury Deposition Observation in Chongqing: Evaluating Effectiveness of Mercury Pollution Control over the Past Decade in Southwestern China

As the largest Hg reservoir in terrestrial ecosystems, forests provide valuable insights into atmospheric Hg levels through observations of mercury deposition. In this study, we conducted a one-year observation of Hg deposition, by both throughfall and litterfall, in a forest located in Chongqing, an industrial hub in southwestern China, in 2021. We compared the results with observations made at the same sampling site in 2010–2011. The results showed that there were significant decreases in both Hg concentrations (from 115 μg·kg–1 to 80.2 μg·kg–1 for litterfall and from 68.4 ng·L–1 to 4.01 ± 2.09 ng·L–1 for throughfall) and Hg deposition fluxes (from 89.8 μg·m–2·yr–1 to 19.9 μg·m–2·yr–1 for total deposition, decreasing by 77.8%) in the forest from 2010 to 2021. The decrease in deposition might result from the synergistic effect of reduction in both anthropogenic (inventory-listed or nonquantitative) and re-emission sources. Over the decade since the initiation of the Minamata Convention on Mercury, atmospheric Hg levels have decreased significantly, mainly due to the co-benefits of conventional air pollutant control, indicating the effectiveness of China’s Hg pollution control policies.