Wildfire Smoke Increases Ground-Level Ozone and Excess Deaths

Research assessing the effects of wildfires over two decades indicates that wildfire smoke significantly raises ground-level ozone, contributing to more than 2,000 excess deaths per year in the United States.

The study, published in Science Advances, suggests that the true health toll of wildfire smoke is likely higher than previously estimated because prior research has largely focused on dangerous particulates while overlooking the impact of ozone.

Ozone is an invisible gas and a strong oxidant. When humans are exposed to increased levels of ground-level ozone, it is linked to several health complications, including cardiovascular and respiratory problems, as well as reduced cognitive performance and increased mortality.

The research was led by Yangmingkai Li, a visiting undergraduate researcher at Stony Brook University’s School of Marine and Atmospheric Sciences (SoMAS), and Minghao Qiu, an assistant professor at SoMAS and core faculty member in the Program in Public Health at Stony Brook University.

According to Qiu, scientists have primarily focused on the impacts of particulate matter pollution from wildfires but have lacked a systematic understanding of how these fires affect ozone levels across the U.S.

Analysis of Two Decades of Air Quality Data

To quantify changes in surface ozone concentration during fire episodes, the researchers combined nearly two decades of surface ozone measurements from 2006 to 2023. This data was integrated with meteorological data and satellite information using machine learning models.

The team utilized the National Oceanic and Atmospheric Administration (NOAA) Hazard Mapping System (HMS) smoke plume product to identify smoke days. This allowed the researchers to compare surface ozone measurements on smoke days versus non-smoke days while controlling for ultraviolet radiation and ambient temperature.

The findings revealed that wildfire smoke boosts daily ozone by as much as 16% in certain regions of the U.S., specifically in the Midwest and the eastern part of the country. This increase is significant enough to drive higher rates of illness and death.

Due to the nature of the exposure-response functions used in the study, which were derived from data on elderly populations, the researchers estimated and reported mortality specifically for individuals aged 65 and over to ensure consistency.

The Risk of Invisible Pollution

A critical finding of the study is that air quality risks persist even when smoke is no longer visible. Because particulate matter pollution and ozone pollution do not often overlap, days with relatively good visibility following a wildfire may still contain harmful levels of unseen ozone.

This disconnect between visibility and air safety means that the public and health officials may underestimate the risks associated with post-fire environments.

the research team noted that these ozone increases represent a hurdle to clean-air progress. The rise in ozone levels caused by wildfires partially cancels out the long-term nationwide declines in ozone mortality and ozone levels.

“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,” said Minghao Qiu, corresponding author, assistant professor in the School of Marine and Atmospheric Sciences (SoMAS) and core faculty in the Program in Public Health at Stony Brook University.

Minghao Qiu

The study was supported in part by the NOAA Climate Program Office’s Atmospheric Chemistry, Carbon Cycle, and Climate Program, as well as the Minghua Zhang faculty career catalyst award at SoMAS and Stony Brook University.