As coal plants across the United States shutter and stop pouring harmful pollutants into the air, the health effects from all those emissions have eased, saving thousands of lives. But less pollution from coal doesn’t mean all pollution has disappeared, and now fuel sources besides coal are having a bigger impact on our health. Across the country, Harvard researchers found, the negative health impacts from burning natural gas, biomass, and wood are beginning to outweigh those from burning coal.
In the last few decades, electricity generation has moved away from coal toward other, more sustainable options—and most of the research on this transition has focused on what this means for greenhouse gas emissions, says Jonathan Buonocore, a research scientist at the Center for Climate, Health, and the Global Environment at the Harvard Chan School for Public Health and the lead author of the study, published in the journal Environmental Research Letters. “The gap that we wanted to fill was that there hasn’t been similar research on the health implications across the life cycle,” he says.
For the study, which was supported by the nonprofit Rocky Mountain Institute, researchers focused on PM2.5—tiny particles of pollution that measure 2.5 micrometers or less. These particles are small enough to penetrate into lungs and the bloodstream, causing or worsening health issues from asthma to strokes to neurological disease, though the Harvard researchers looked only at how PM2.5 exposure affected mortality broadly.
PM2.5 is regulated by the EPA, so they combined EPA emissions data with data from the Energy Information Administration about energy use by source, sector, and state. Then they used models to estimate the mortality in each county from both PM2.5 and PM2.5 precursors—ammonia emissions, for example, can turn into PM2.5 when combined with other air pollutants such as nitrogen—associated with stationary fuel sources from 2008 to 2017. “Stationary” means fuel sources in all sectors except transportation, so not only coal and natural gas plants, but industrial boilers and residential and commercial buildings that burn wood or biomass (which includes fuels such as wood pellets and agricultural waste).
In 2017, all those stationary sources were responsible for an estimated $524 billion to $777 billion in health impacts, and 47,000 to 69,000 premature deaths. Of those deaths, up to two-thirds—33,000 in the lowest mortality estimate and 53,000 in the highest—were due to fuel sources other than coal. Coal was still the most harmful fuel when it came to electricity generation, but gas, biomass, and wood were the most harmful in buildings and industrial boilers. Gas emissions led to more deaths than coal emissions in at least 19 states.
“What this really points to is if you replace one combustion fuel for another combustion fuel, that is not a pathway to get you to a healthy energy system,” Buonocore says. (Solar and wind are examples of noncombustion energy sources.) As the share of coal-generated electricity continues to go down, so will its health impacts—but then this trend of gas, biomass, and wood accounting for more health issues will also grow, the study authors say. In that sense, electricity generation may not be the largest source of harmful pollutants going forward; we may have to pay more attention to what energy systems are in our buildings, too, because it’s not just those living near power plants affected by this pollution.
Though greenhouse gas emissions may be down as a result of using wood or natural gas (while natural gas is a fossil fuel, it emits fewer carbon dioxide emissions than coal), the research that only focuses on CO2 or methane emissions may “lose sight,” Buonocore adds, of other pollutants that are harmful to our health. “For any decision made on the energy sector,” he says, “it’d be really useful if both the climate implications and the health implications were evaluated in tandem and on equal footing with each other.”