A new study finds that increasingly intense wildfires are erasing decades of air quality gains for the most vulnerable: babies in the womb. Smoke from wildfires now contributes more to harmful prenatal exposures than pollution from vehicles, factories and other human sources, according to researchers at the University of Maryland, College Park.
Since the 1970 law and its amendments were passed, combined emissions of six harmful air pollutants from vehicles and industrial sources have dropped by nearly 80 percent. But mounting evidence shows that wildfire smoke is overshadowing those improvements. The unchecked burning of fossil fuels has created warmer, drier conditions that make wildfires more intense and blanket communities in toxic smoke that is more harmful than other types of pollution.
The new study, published Thursday in Frontiers in Environmental Health, is the first to show that wildfire smoke is systematically offsetting prenatal air quality gains for unborn babies, the researchers said. Low-income, rural and Indigenous populations bear a disproportionate burden of wildfire-related poor air quality, they found.
Senior author Michel Boudreaux, associate professor of health policy and management, said the study focuses on a very specific population that is quite at risk for adverse health outcomes. “We were looking at infants that were born and what their exposure was like during the prenatal period,” he said. Prenatal exposure to wildfire smoke significantly increases the likelihood of premature birth, low birth weight, and later-life risks of chronic respiratory conditions and other diseases.
The team analyzed air pollution data from the Environmental Protection Agency and live birth records across the contiguous United States from 2003 to 2019. They used computer models to estimate exposures to fine particle pollution, or PM2.5, from human sources like cars and industry, as well as natural sources like wildfires. By modeling air quality without fire emissions, they calculated how much pollution came from wildfires.
The dataset covered nearly 65 million babies born over 16 years. The researchers determined how many days each baby was exposed in the womb to the EPA threshold for unhealthy air. Average daily prenatal exposure to human-source pollution fell by 37 percent during that period, but wildfire contributions doubled, wiping out those gains.
The study does not integrate data on preterm birth, birthweight or other outcomes, but it is a very good exposure-characterization study, said Ilona Jaspers, an inhalation toxicologist and professor of pediatrics at the University of North Carolina at Chapel Hill, who was not involved in the research. “What this study does do well is confirm and expand the well-established finding that ambient PM2.5 in the United States is increasingly wildfire-dominated, offsetting Clean Air Act gains, but applies a birth-weighted lens to it,” she said.
Jaspers noted that wildfire smoke exposures are likely to have vast public health consequences. In previous studies, she and colleagues used prescription insurance claim data to show that exposure during specific perinatal periods can lead to childhood respiratory diseases.
Boudreaux acknowledged limitations: the study does not account for how much time mothers spent outdoors, whether they wore N95 masks, or whether they had home air filtration. But he pointed to data sources like Purple Air that detect large amounts of PM2.5 pollution inside homes during wildfire events.
The study highlighted regions where wildfire contributions to air pollution more than doubled, especially the West and Northwest. Communities experiencing the largest reversals in air quality, often low-income, rural, and American Indian and Alaska Native populations, also tend to have the least access to neonatal care.
Because exposure to wildfire smoke early in life can cause lifelong health problems, reducing prenatal exposure will yield long-term benefits, Boudreaux said. He noted that the last six years have seen catastrophic fires in the West and Canada, and extending the study through 2026 would likely show an even higher wildfire contribution, though he called that speculation.
Boudreaux said wildfire smoke now accounts for an increasing share of “acute, massive air pollution days” that endanger babies’ health. “What that tells me is that the next frontier is how do we help people manage exposure to wildfire smoke, which is a different kind of exposure than ambient pollution from other sources.” That means providing communities with clean-air shelters, air filters and better access to healthcare when exposures occur. “Ultimately, we should be asking, are there things we can do to reduce the risk of climate change in general?” he said.
