Pollution From U.S. Coal Power Killed 460,000 People in Two Decades — Study

Power plants that burn coal might be responsible for more deaths than initially thought, and have contributed to the deaths of hundreds of thousands of people, new research has found.

Exposure to coal PM2.5, which are tiny air pollutants released by burning coal, has a mortality risk 2.1 times higher than PM2.5 pollutants emitted by other sources, a new paper in the journal Science has found.

The study said that 460,000 deaths between 1999 and 2020 could be attributable to coal-burning power plants—most of which occurred between 1999 and 2007—with 10 of these plants each responsible for at least 5,000 deaths.

Coal PM2.5 has been previously assumed to be no more deadly than PM2.5 from any other sources. These findings imply that the benefits of reducing coal emissions may be greater than previously thought.

"When coal is burned, it emits many chemicals including SO2, nitrogen oxides, black carbon particulate matter, and metals. The mix of chemicals emitted from coal plants is different than the mix of chemicals from other PM2.5 sources like diesel trucks, wildfires, etc.," Lucas Henneman, co-author of the paper told Newsweek.

Henneman is an assistant professor in the Sid and Reva Dewberry Department of Civil, Environmental, and Infrastructure Engineering at George Mason University.

The rate of deaths from PM2.5 has been much lower in recent years: an average of 43,000 deaths per year were due to coal PM2.5 between 1999 and 2007, but by 2020, this had reduced to 1,600 annual deaths. The researchers suggest that this is likely thanks to regulations on burning coal and the release of coal PM2.5.

"SO2 was historically the largest portion of PM2.5 from coal, and EPA (Environmental Protection Agency) regulations and coal power plant closures led to big decreases in SO2 emissions across our study period. These decreases in SO2 emissions led to large decreases in coal PM2.5 across the period," Henneman said.

Coal PM2.5 is comprised of tiny particles that are 2.5 microns or less in diameter, including sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water, which can cause irritation to the nose, eyes, lungs and throat, and lead to increased chance of respiratory infections. Some of these substances form as a result of sulfur dioxide reacting and breaking down in the atmosphere.

The researchers calculated the mortality rate of coal PM2.5 using models, inputting emissions data from 480 coal power plants and geographical data of how coal sulfur dioxide is blown in the wind and converted in the atmosphere to PM2.5. This generated a PM2.5 exposure field for each power plant. Using Medicare records, the researchers investigated the health statuses of thousands of U.S. citizens, amassing 650 million person-years worth of health data, which they then compared against the PM2.5 exposure fields.

"We collected data on the amount of SO2 emitted from each of the 480 power plants in operation at any point from 1999-2020. We then used a model to track how the wind transported that SO2 and how it transformed in the atmosphere to PM2.5," Henneman explained.

"We matched this coal PM2.5 exposure to data on Medicare recipients—almost all Americans 65 years and older—including where they lived and when they died. We found that, in areas with higher coal PM2.5, the mortality rate was higher than in areas without coal PM2.5."

They found that 460,000 deaths were related to coal PM2.5, which represented 25 percent of all PM2.5-related deaths before 2009, and 7 percent after 2012. They also found that in 1999, PM2.5 had an average concentration of 2.34 micrograms per cubic meter of air (μg/m3), which had dropped to 0.07 μg/m3 by 2020.

"Knowing the exposure (coal PM2.5) and the mortality rate from coal PM2.5 allowed us to calculate the total mortality burden from coal power plants in the U.S. We found that 460,000 deaths in the Medicare Population were linked to coal PM2.5. Most of these deaths were in the early part of the study, and annual deaths from coal decreased with decreasing emissions," Henneman said.

The researchers determined that a 1μg/m3 increase in annual average coal PM2.5 was linked to a 1.12 percent increase in all-cause mortality, giving it a 2.1 times greater mortality risk than PM2.5 from any other source.

Some of this study's limitations are listed in a Perspective article also released in Science, which details how the paper only focuses on SO2 emissions and the secondary PM2.5 that resulted rather than direct PM2.5 released by the power plants, which may also have contributed towards the mortalities near the power plants.

Regardless, the researchers hope that their study will highlight the importance of reducing the number of coal-burning power plants across the U.S. and moving towards less harmful methods of energy generation.

"There have been major reductions in coal burning for electricity in the United States since 1999, with the biggest reductions occurring since 2007. The reductions are due to EPA regulations, decreased electricity demand during and after the 2008 recession, and coal power plants closing down in favor of utilities increasingly adopting natural gas to generate electricity, starting in the early 2010s," Henneman said.

"The best path away from coal air pollution is to adopt renewables for electricity generation like wind and solar. Natural gas, which is cleaner-burning than coal, has served as an intermediate to reduce coal over the past 10 years, but it still has negative impacts on air pollution, climate, and the environment."

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