Mercury is a pollutant that poses a serious threat to humans and ecosystems. In particular, mercury is known to spread to distant areas through the atmosphere.
An international research team has revealed for the first time the role of the stratosphere in the dispersion of mercury. The research team, including scientists from the Massachusetts Institute of Technology, announced on the 9th that the Earth's stratosphere has a significant impact on the transport and deposition of mercury. The research findings were published in the international journal 'Science Advances.'
Mercury is released into the atmosphere not only from natural causes such as volcanic eruptions, geological activity, and ocean surface evaporation but also from human activities such as fossil fuel combustion, gold mining, industrial activities, and waste incineration. The Northern Hemisphere, which is more densely populated and industrially active than the Southern Hemisphere, emits about 2.5 times more mercury. However, the concentration of mercury in the atmosphere is approximately 1.5 ng/m³ in the Northern Hemisphere and about 1.0 ng/m³ in the Southern Hemisphere, indicating that the difference in concentration is not as large as the difference in emissions. This is because some of the mercury emitted in the Northern Hemisphere is transported to the Southern Hemisphere through atmospheric circulation.
Scientists have primarily analyzed the chemical reactions, transport, and deposition processes of mercury within the troposphere to understand how mercury moves. The troposphere is the layer of atmosphere approximately 10 km thick above the Earth's surface, containing 90% of the atmospheric mass. However, an approach focused solely on the troposphere could not fully explain the transport of mercury from the Northern Hemisphere to the Southern Hemisphere and the accumulation of mercury in polar regions.
The research team integrated the reactions and movement mechanisms of mercury that can occur in the upper and lower parts of the stratosphere, the atmospheric layer directly above the troposphere, into atmospheric circulation models to analyze the movement of mercury. This is the first study to quantitatively analyze the impact of the stratosphere on the movement of mercury and ecosystem pollution.
According to the study, about 20% of the mercury emitted from human activities has reached the stratosphere. In the stratosphere, it was found that between 5% and 50% of the mercury on the Earth's surface is oxidized into a stable form that can exist for a long time. Notably, the lower part of the stratosphere, about 5 km thick, was a 'hot spot' for mercury oxidation. In this process, the oxidized mercury from high-emission areas in the Northern Hemisphere moved to polar regions and mid-latitude areas in the Southern Hemisphere as if on a conveyor belt through stratospheric circulation. In fact, about 52% of the mercury emitted from the Northern Hemisphere is revealed to move to the Southern Hemisphere through the stratosphere.
The research team explained that the oxidized mercury in the stratosphere exists in a stable compound form, which contributes to ecosystem pollution in distant areas as it descends into the troposphere. If the current trend of greenhouse gas emissions continues, it is predicted that the concentration of mercury in the global stratosphere could increase by up to 12% by the end of the 21st century due to changes in stratospheric circulation caused by climate change. This increasing trend is expected to be more pronounced in tropical ocean surfaces and high-latitude regions.
The research team noted, 'These findings provide a new perspective on the problem of mercury pollution in ecosystems that can have serious impacts on human and wildlife health,' adding, 'The risk of mercury poisoning is likely to increase as climate change progresses. Preventive measures through emission reductions are necessary.'
Reference materials
Science Advances (2025), DOI: https://doi.org/10.1126/sciadv.ads1459