The Minamata Convention on Mercury, a global treaty adopted by the United Nations in 2013, aims to reduce worldwide mercury pollution by setting limits on specific pollution sources and prohibiting new mercury mining. Certain aspects of the treaty are still under negotiation: For instance, nations have the flexibility to create their own plans for reducing mercury emissions from some sources, such as coal-fired power plants. How nations choose to address these emissions could significantly impact global mercury pollution, since coal-fired power plants are responsible for about a quarter of mercury emissions worldwide.
MIT Engineering Systems Division graduate student Amanda Giang, a research assistant in the MIT Joint Program on the Science and Policy of Global Change, co-authored a recent study published in the journal Environmental Science & Technology that evaluates different ways India and China might address coal-fired power plants. The research was supported in part by the National Science Foundation.
Q. Why study India and China?
A. Whatever China and India do to reduce their mercury emissions will have the biggest impact on future global mercury levels. China is currently estimated to emit about a third of global emissions, and India is the second-largest source at 7 percent. These emissions come from a variety of activities — mining, cement production, metal smelting — but coal combustion for industry and electricity generation is one of the biggest sources in these countries, and this source is expected to grow as economies develop.
Mercury from power plants travels worldwide, but is also deposited in ecosystems close to where it is emitted. That means countries have a strong domestic incentive to decrease mercury emissions. That is, the benefits of reduced pollution will be most strongly felt where the cuts are made, in addition to at the global level. So, a strict emissions standard for coal-fired power plants will not just benefit other countries, it would benefit India and China domestically.
Q. How do you measure the treaty’s benefits?
A. We measure benefits as avoided future mercury emissions. So we compare what would have been emitted under current pollution-control technologies to what would be emitted under a few different ways of achieving the requirements outlined in the convention, either through stricter technology requirements, or system-wide changes in the energy system. There are many technologies that can reduce mercury pollution, some already widely in use. We also model how mercury emissions travel through the atmosphere and enter ecosystems under these different scenarios.
The decisions that convention negotiators make about the stringency of the technology requirements for coal power plants will make a big difference in avoided emissions. Convention negotiators want to strike a balance between requiring strong pollution control and allowing flexibility for different countries’ economic and technical capacities. Through analysis of existing studies, policies, and interviews with convention negotiators, we identify technologies that India and China would be likely to adopt if they were given a lot of flexibility. We find that putting these technologies in place avoids about 12 percent of current-day emissions. Requiring stronger, but technologically feasible pollution-control technologies avoids another 8 percent — an amount equivalent to India’s total present-day emissions.
Q. So far, you’ve covered how to avoid increases in mercury pollution. Is there any way to actually decrease emissions?
A. Emissions-control technologies can slow emissions growth, but alone, they likely won’t keep total mercury emissions from growing as China and India consume more coal to fuel their energy needs. The most effective way to lower mercury emissions below present-day levels would be combining control technologies with a transition away from coal as a power source. Under a global transition to low-carbon energy sources, we could see a decrease in emissions from the power sector. In India though, where power sector growth is anticipated to meet energy access needs, we could still see an increase in emissions in the future despite control policies.
It’s important to keep in mind that whatever mercury is released into the environment now doesn’t stay where it’s deposited. Mercury that is deposited in the environment can easily cycle through the rest of the ecosystem for decades, ending up in the air, water, and land. So, whatever decisions are made about how to reduce mercury emissions now will continue to affect us in the future.