Wildfire Smoke Raises Ground-Level Ozone and Excess Deaths in the U.S., Study Finds

Wildfire smoke poses a greater health threat than previously understood, according to a new study published in Science Advances. The research, led by Minghao Qiu of Stony Brook University and collaborators, demonstrates that wildfire smoke significantly raises ground-level ozone levels, contributing to excess deaths in the United States each year.

Previous studies on wildfire smoke and its health impacts have largely focused on dangerous particulates emitted by fires, often overlooking the role of ozone. While invisible, ozone is a potent oxidant linked to respiratory and cardiovascular problems, reduced cognitive performance, and increased mortality.

“As we move further into spring and summer, wildfires will likely intensify across the United States and North America,” says Qiu, corresponding author and assistant professor at Stony Brook University’s School of Marine and Atmospheric Sciences (SoMAS). “Scientists must consider the effects of increased ozone from fires in addition to the particulates already known to pollute the air.”

Study Methodology and Key Findings

The study, led by Yangmingkai Li, a former visiting undergraduate researcher in Qiu’s group at SoMAS, addresses a critical gap in wildfire research. While scientists have extensively studied wildfire impacts on particulate matter pollution, they lacked a systematic understanding of wildfire effects on ozone across the U.S.

To quantify changes in surface ozone concentration during fire episodes, the researchers combined nearly two decades of data (2006–2023), including:

• Surface ozone measurements
• Meteorological data
• Satellite data
• Machine learning models

They also utilized the NOAA Hazard Mapping System (HMS) smoke plume product to identify smoke days and compare ozone levels between smoke and non-smoke days. The analysis controlled for ambient temperature and ultraviolet radiation.

Ozone Levels Surge by Up to 16% in Some Regions

The findings reveal that wildfire smoke raises ground-level ozone and boosts daily ozone levels by as much as 16% in certain U.S. regions—particularly the eastern U.S. and Midwest. This increase is significant enough to worsen illnesses and contribute to smoke-related deaths.

Using their compiled data and models, the research team estimates that wildfire smoke ozone increases excess U.S. deaths by more than 2,000 annually.

Critical Insights and Public Health Implications

Qiu emphasizes two key takeaways from the study:

1. Underestimated health risks: The true health effects and death toll from wildfire smoke are likely higher than previously thought, as prior research has not accounted for ozone exposure.
2. Invisible threat persists: Even on days with relatively good visibility following wildfires, harmful ozone may still be present. Particulate matter and ozone pollution do not always overlap, meaning areas with seemingly clean air may still harbor unseen health hazards.

The study’s exposure-response functions were derived from data on the elderly population, leading the researchers to estimate and report mortality only for individuals aged 65 and older for consistency.

The research team notes that their findings regarding ozone level increases from wildfires are preliminary and warrant further investigation.