Wildfire smoke's hidden ozone threat may be adding thousands of US deaths each year - Earth - Environment

Ground-level ozone in the form of smog, shown here in Denver, can affect human health post wildfires, even if the smoke from fires is not visible. Credit: NREL

A study that assesses the effects of wildfires over two decades shows that wildfire smoke significantly raises ground-level ozone and contributes to excess deaths from wildfire smoke in the United States each year. The research, led by Minghao Qiu, Ph.D., of Stony Brook University, is published in Science Advances.

Why ozone from fires matters

Previous research about wildfire smoke, its health risks, and impact on excess deaths, has largely overlooked ozone and concentrated more on dangerous particulates emitted from fires. Ozone is invisible, but it is a strong oxidant. When humans are exposed to more ozone it is linked to several health issues such as respiratory and cardiovascular problems, reduced cognitive performance, as well as increased mortality.

"As we move further into spring and then summer, wildfires will most likely increase in the United States and all of North America, and scientists should be thinking about the effects of increased ozone from fires in addition particulates emitted into the air," says Qiu, corresponding author, Assistant Professor in the School of Marine and Atmospheric Sciences (SoMAS), and Core Faculty Member of the Program in Public Health at Stony Brook University. The study is led by Yangmingkai Li, who was a visiting undergraduate researcher in Qiu's group at SoMAS.

Surface O₃ concentrations increase on smoke days across the US. Credit: Science Advances (2026). DOI: 10.1126/sciadv.aec2903

How the team measured ozone changes

Qiu says that scientists have primarily focused on wildfire impacts on particulate matter pollution but have not had a systematic understanding on wildfire effects on ozone over the U.S. This study combined nearly two decades of surface ozone measurements (2006 to 2023), meteorological data, and satellite data using machine learning models to quantify the changes in surface ozone concentration during fire episodes across the continental U.S.

They also used the satellite-based National Oceanic and Atmospheric Administration (NOAA) Hazard Mapping System (HMS) smoke plume product to determine smoke days and compare surface ozone measurements across smoke days and non-smoke days while controlling for ambient temperature and ultraviolet radiation.

Using the compiled data and machine learning models, the researchers discovered that wildfire smoke raised ground-level ozone and boosts daily ozone by as much as 16% in some U.S. regions—such as the eastern part of the country and Midwest—an amount significant enough to increase illnesses and deaths caused in part by smoke from fires. The team also estimates that wildfire smoke ozone increases excess U.S. deaths per year by more than 2,000.

Hidden risks and vulnerable groups

Qiu emphasizes that two important concepts are critical to their results: (1) The true health effects and death toll from wildfire smoke are likely higher than previously thought, given that prior research has not factored in ozone exposure, and (2) Even days with relatively good visibility post wildfires—may still contain the unseen ozone from the fires that harm health, because particulate matter pollution and ozone pollution do not often overlap.

In this study, some of the exposure-response functions are specifically derived from data on the elderly population. Therefore, the researchers only estimated and reported mortality for people ages 65 and over for consistency.

The research team also points out that their findings related to ozone level increases from wildfires are another hurdle that erodes clean-air progress, partially canceling out long-term declines in ozone levels and ozone mortality nationwide. 

Provided by Stony Brook University 

by Stony Brook University

edited by Lisa Lock, reviewed by Robert Egan 

Source: Wildfire smoke's hidden ozone threat may be adding thousands of US deaths each year