Burning fossil fuels emits air pollutants, including mercury. Photo: @mattartz via Unsplash/Squarespace
When we talk about mercury pollution with various audiences, we are often asked about its connection to the challenge of addressing other air pollutants and climate change more broadly: How do mercury emissions relate to other air pollutants and carbon emissions? Do stories about mercury provide any lessons for today’s efforts to phase out the use of fossil fuels? We argue in chapter 5 that analyzing the mercury issue provides several useful insights to those who are grappling with how to mitigate regional air pollution as well as global climate change.
The future of mercury emissions from large industrial sources is intimately tied to other air pollution issues and climate change. We start chapter 5 with a story of Steubenville, Ohio. Almost 50 years ago, Steubenville was identified in a famous six-cities study as one of the cities in the United States with the worst air quality. Since then, the air in that part of Ohio as well as in many other regions of the United States has become much cleaner. This has been due to both increased regulations and a gradual closing of heavy industrial manufacturing. The latter often resulted in a painful reconstruction of the local economy, as many factory workers lost their jobs, affecting them and their family members. And the United States still face the enormous challenge of significantly cutting emissions of carbon dioxide and other greenhouse gases.
Extensive burning of fossil fuels during the industrial era has resulted in the emission of large amounts of hazardous substances into the atmosphere, including carbon dioxide, sulfur as well as mercury. As we discuss in chapter 3, different forms of mercury can travel via air currents over shorter and longer distances, harming populations both nearby and far away. Air pollution controls and reduced reliance on coal, especially in North America and Europe, have resulted in a reduction in emissions of mercury and other harmful substances with many environmental and human health benefits. However, carbon dioxide emission continues at high levels, contributing to climate change.
Some air pollution controls reduce multiple pollutants, including mercury and sulfur, simultaneously. Air pollution control devices – often “end-of-pipe” technologies – on industrial point sources capture these pollutants before they are emitted to the atmosphere. The fact that different air pollution control devices capture varying amounts of different forms of mercury has implications for how far emitted mercury can travel in the atmosphere and where it deposits. Some control technologies preferentially capture more soluble (oxidized) or particulate forms of mercury that tend to travel mainly regionally. More advanced controls such as activated carbon injection can control elemental mercury emissions, which travel globally. This process can capture as much as 98 percent of mercury emissions.
End-of-pipe controls prevent mercury emissions to the atmosphere, but importantly they do not change the total amount of mercury removed from fossil fuel reserves. The fact that mercury is captured by end-of-pipe technology raises new technology and governance issues. Mercury-containing fly ash from a coal-fired power plant, for example, may be later reused. When fly ash is heated to high temperatures as a component in making cement, mercury can be emitted to the atmosphere unless appropriate control technology is present in the cement factory. Thus, if byproducts are not properly disposed of or used in environmentally safe ways, at least some of the previously captured mercury can be emitted from these industrial point sources.
Most national and regional action on mercury emissions from large point sources have relied on an incremental introduction of stricter pollution control technologies rather than seeking to shift underlying activities of coal-burning and industrial production. The Minamata Convention, due to political resistance from many of the world’s countries, would not exist today had the treaty sought to restrict coal use; rather, the Minamata Convention mandates the application of control technologies on large industrial sources to mitigate mercury emissions. This approach is less ambitious than an alternative that would have looked to phase out coal burning. Yet, the existence of technology-based mandates under the Minamata Convention may push countries to adopt them at a faster pace than they otherwise would have done and strengthen standards over time. This helps reduce mercury deposition both in the present and future with clear human health benefits.
The Minamata Convention was agreed in 2013, two years before the Paris Agreement, and would not exist today had the treaty sought to restrict coal use. Photo: N. Selin.
The mercury case shows that technology-based approaches can, under some conditions, lead to more fundamental change. Mercury standards in the United States and Canada accelerated the closing of some coal-fired power plants that were too old or unprofitable to warrant the addition of new end-of-pipe technology. This illustrates how dynamics that lead to gradual progress toward sustainability and more disruptive change can be simultaneously present and reinforcing. At the same time, the application of control technology that mitigate mercury emissions and other local pollution problems may extend the operability of modern coal-fired power plants in China and other mainly Asian countries, slowing down efforts to cut carbon dioxide emissions and address climate change. We further discuss issues around these types of trade-offs and broader lessons for sustainability transitions in chapter 8.