Thanks to the phase-down of coal, the risk of premature death in the United States due to the burning of fuels for electricity, homes and businesses fell 54 to 60 percent from 2008 to 2017, Harvard researchers found in a new study.

But their results showed that fuel use in buildings still accounts for a significant health burden, causing an estimated 48,000 to 64,000 premature deaths in 2017, with the hazards of burning biomass, natural gas and wood now surpassing those of coal.

The study has implications for policymakers at federal and state levels who are designing aggressive plans to decarbonize buildings. If they focus on reducing greenhouse gas emissions alone, without taking into account other air pollutants, they could be encouraging fuel switching that will perpetuate health risks in some communities.

“Swapping one air pollution-emitting fuel source for another is not a pathway to a healthy energy system,” wrote the team from the Harvard T.H. Chan School of Public Health in their paper, published Tuesday in Environmental Research Letters. “Inclusion of health in energy policy may be necessary for true primary prevention of a large portion of disease burden in the U.S.”

The researchers believe their study is the first to provide an inventory of the health impacts of the building energy transition that has taken place over the past decade.

Using the most recent available data from the U.S. Environmental Protection Agency and the Energy Information Administration, the researchers focused only on stationary sources of pollution (as opposed to those from transportation), where the greatest transition in energy use has occurred. They used three different computer models to estimate the health impact of the pollution generated by power plants, industrial and commercial boilers and residential energy use.

The study focused on fine particulate matter 2.5-microns wide, known as PM 2.5, a pollution from combustion that a long line of studies has shown is associated with premature death from cardiovascular and respiratory diseases. The researchers also tracked several key pollutants that are precursors to both PM 2.5 and ground-level ozone, or smog, including sulfur dioxide (SO2), nitrogen oxides (NOx) and volatile organic compounds (VOCs). 

The biggest change, they found, was a reduction in the health burden from power plant pollution, which accounted for 10,000 to 12,000 premature deaths in 2017, down from 59,000 to 66,000 in 2008. But for industrial boilers and commercial buildings, the health impacts of sulphur dioxide from coal and oil were essentially replaced by those from the PM 2.5 pollution generated from their switch to biomass combustion.

By 2017, biomass and wood had become the leading sources of health impacts from stationary-source air pollution in 24 states. Natural gas combustion emissions from stationary sources led to more deaths than emissions from coal did in at least 19 states, the researchers calculated.

The researchers said they hoped the data on the lingering health impacts of switching to natural gas or biomass would help inform policymakers who are embarking on major climate policies that will lead to investments in long-lasting energy equipment and infrastructure.

“Some of these policies that we are studying and we are looking at, unfortunately, are not considering hazardous air pollutants that are drivers of health impacts or mortality in their design,” said co-author Parichehr Salimifard. “Therefore, they are not as beneficial as they could have been.”

For example, in 2018, President Donald Trump’s first Environmental Protection Agency Administrator, Scott Pruitt, declared biomass a “carbon neutral” energy source. That was not a move that had any immediate practical effect, since the Trump administration was rolling back carbon pollution standards anyway.

But the treatment of biomass certainly will be an issue in the design of the federal clean energy standard that President Joe Biden plans to put into place. As part of New Hampshire’s renewable energy program, the state has incentives available for homes as well as industrial and commercial boiler operators to convert to wood pellet systems. New York City’s Local Law 97 sets carbon caps for the city’s largest buildings beginning in 2024, but doesn’t set limits on other types of pollutants. As a result, said Salimifard, it could end up encouraging moves to biomass or gas. The Urban Green Council estimates that there will be some $20 billion in retrofits made to buildings to comply with Local Law 97.

Patrick Kinney, an air pollution epidemiologist at Boston University Public School of Health, who was not involved in the study, said that the modeling tools used by the Harvard team are the best available for a quick, comprehensive analysis across multiple years, pollutants and source classes. “But they are still models, so we should view these results as intriguing suggestions of trends and relative rankings rather than definitive quantifications of impacts,” Kinney said.

He added that the researchers, as happens in most studies, used EPA guidance that judges all kinds of PM 2.5 equally deadly. However, some studies have found that biomass PM is less toxic than the pollution from fossil fuel, an issue that will require further study if the impetus grows for switching to biomass.

Kinney, who has worked with one of the co-authors on another study, said the Harvard team’s methods were sound and appropriate.

“The questions they pose are important ones,” he said.

An earlier version of this article incorrectly identified in two paragraphs the type of fuel the new research found still accounted for significant health effects. It was fuels that involve combustion, not fossil fuels.