A landmark study has found air pollution from coal-fired power stations was the cause of 460,000 US deaths over the last two decades.
The data, published today in the journal Science, results from the longest-running study of its kind in the US. Similar research has been conducted in Australia.
The report says exposure to fine particulate matter – known as PM2.5 – from coal burning in American power plants, is twice as deadly as pollution from other human activities. PM2.5 from coal stations tends to contain sulphur dioxide (SO2), a known lung and airway irritant.
The mortality impact is much higher than previous calculations, with the substantial, nationwide dataset used by the research group suggesting previous local research underestimated the risk of exposure to ‘coal PM2.5’.
The study was led by Dr Lucas Henneman, an environmental engineer and assistant professor at George Mason University in Virginia. They isolated coal PM2.5 from other sources for the calculations, which were performed using Medicare records and emissions data from 480 US coal-fired power stations between 1999 and 2020.
Most of the 460,000 deaths occurred during peak levels of PM2.5 emissions up to 2007. Overall, deaths in this period accounted for a quarter of all deaths related to PM2.5 exposure.
Henneman says the research, which was funded by several organisations including the US National Institutes of Health and Environmental Protection Agency, demonstrates the elevated risk of particulates from coal-based electricity generation.
“PM2.5 from coal has been treated as if it’s just another air pollutant, but it’s much more harmful than we thought, and its mortality burden has been seriously underestimated,” Henneman says.
Modelling performed on the movement of coal SO2 and its conversion into PM2.5 allowed Henneman’s team to estimate ‘exposure fields’ surrounding each of the 480 power stations studied.
Combined with Medicare records indicating where people lived and died, Henneman’s team were able to connect PM2.5 exposure to health impacts.
The report recorded average PM2.5 concentrations of 2.3 micrograms per cubic metre of air for US coal power stations. Within two decades, this level had dropped to 0.07 – a 95% decrease over the period.
“Beyond showing just how harmful coal pollution has been, we also show good news: Deaths from coal were highest in 1999 but by 2020 decreased by about 95%, as coal plants have installed scrubbers or shut down,” Henneman says.
Coal power and other sources also a concern in Australia
In Australia, research has been conducted to demonstrate the risks posed by exposure to PM2.5. Averaged over a year, the Australian National Environment Protection Measure for Ambient Air Quality limits PM2.5 levels to 8 micrograms per cubic metre.
PM2.5 is a coverall term for fine particulates measuring 2.5 micrometres or less in diameter – about half as wide as a strand of spider silk, and less than a single E.coli bacterium.
It can refer to tiny specks of material from many sources – including dust from coal, cotton, various metals, minerals, wood and chemical fumes.
“We have significant and concerning exposures episodically with bushfires, and we have ongoing exposures in and around coal mining and coal burning power stations […] along major transport corridors,” says Matthew Peters, a professor of Respiratory Medicine at Macquarie Medical School.
While most places in Australia tend to be within safe ranges for PM2.5, acute exposure, and the source of PM2.5, can be harmful.
“It’s an irritant, it’s bad for your airways, and there’s the evolving bit of knowledge in relation to long-term cancer risk.”
Dr Ivan Hanigan is the director of the World Health Organization Collaborating Centre for Environmental Health Impact Assessment and a senior lecturer at Curtin University’s school of population health. He wasn’t involved in the US study but says improved data analysis will continue pushing up mortality estimates.
“We’re getting better estimates as we do more studies,” says Hanigan, who has collaborated with fellow Australian air quality researchers investigating the impacts of PM2.5 previously.
He points to his own 2020 collaboration between several universities and government agencies. The relative risk function used for their study was 1.062, based on European and North American data. By the time their paper was published, that growing global dataset had already increased that function to around 1.08.
“It’s quite a substantial increase in the risk estimate,” Hanigan says.
That 2020 study found PM2.5 pollution was associated with about 2,616 Australian deaths and an economic burden of $6.2 billion.
“When you work with health economists, they can turn the number of deaths avoided into a measure of the years of life lost prematurely,” Hanigan says.
“They’ve done calculations that suggest people are willing to pay a certain dollar figure for an extra year of life, so if you add all those up, the anthropogenic component of PM2.5 is $6.2 billion per year – and that’s just the willingness to pay.
“If you actually put on top [of that] hospital admissions, procedures and all the associated medical costs, which we can’t estimate with this type of method very easily, it’s really costly.”
