Iowa Study Reveals Wildfire Smoke Reversing Clean Air Gains

For decades, the formula for cleaner air in America was straightforward: tighter rules on cars, stricter controls on factories, and local accountability. It worked. Then it stopped working, and a new University of Iowa study explains why the problem isn't something any mayor or state agency can fix.

The research, published in the journal Science, shows that wildfire smoke is wiping out more than a decade of air quality improvements across the United States. The pollution is coming from hundreds or even thousands of miles away, leaving local communities powerless under current federal regulations.

Cleaner Engines, Fouler Skies

Vehicle emissions reductions helped lower surface ozone, a key component of summer smog, for years. But around 2015, that progress reversed.

Between 2015 and 2024, ozone levels increased by 0.13 parts per billion annually, erasing gains that took over a decade to achieve. The researchers found that without wildfire impacts, ozone levels would have continued falling.

“While U.S. air quality regulations have reduced surface ozone, a pollutant linked to respiratory and cardiovascular diseases, this progress has reversed since around 2015,” said Weizhi Deng, the study’s first author. “Wildfire smoke has become a major driver of increasing ozone pollution, especially in the western and midwestern United States.”

Pollution Without Borders

Here is what makes this especially frustrating for states like Iowa: the pollution doesn't stay near the fire. When trees and plants burn, they release carbon monoxide that can travel long distances through the atmosphere.

When that carbon monoxide reaches new areas, it mixes with local pollution like vehicle exhaust and produces ozone there. Communities hundreds of miles away end up breathing poor air from fires they never see and can't control.

“The bottom line is the air is getting worse in these regions, and the reason is pollutants are being transported long distances from wildfires in the western U.S. and Canada,” said Jun Wang, the study’s corresponding author and associate director of the Iowa Technology Institute. “We show in high spatial resolution how a large part of the continental U.S. has been affected by worsened air quality through surface ozone pollution.”

When 2023 Brought the Smoke Home

Iowans don't need a study to tell them the air got bad. The summer of 2023 proved the point when Canadian wildfires sent thick smoke across the Midwest. Surface ozone spiked above federal air quality limits for 148 million Americans.

In the Midwest, the air remained unsafe for more than a week. The pollution reached as far as New York, Texas, and Georgia.

The health toll was severe. Researchers linked smog to 7,974 premature deaths in 2023 alone. Since 2013, wildfire-related ozone has caused more than 300 additional premature deaths each year, with major spikes in 2020, 2021, and 2023.

An EPA Rulebook Built for the Wrong Problem

This is where government accountability comes in. The Environmental Protection Agency sets national ozone standards, but the actual work of cleaning the air falls to states and cities. That arrangement works when the pollution source is a local factory or highway. It collapses when the source is a wildfire burning outside any local authority's jurisdiction.

The system does offer an escape hatch. States and cities can file an “exceptional event claim” with the EPA, arguing that a pollution spike came from something beyond their control. But the burden of proof falls entirely on local and state authorities.

“When air quality is poor, even when the pollution is from elsewhere, the responsibility is on the local or state authority to collect the evidence and then file an ‘exceptional event claim’ to the EPA,” Wang said. “That could be fine, but those exceptional events are not becoming exceptional anymore.”

In other words, the federal government holds local communities responsible for pollution they didn't create and can't control, while the events driving that pollution become routine. It is a regulatory framework that punishes the wrong people.

How Researchers Connected the Dots

The University of Iowa team measured ozone pollution across the continental United States from 2003 to 2024. They combined satellite observations with data from roughly 1,000 ground monitoring stations and used deep learning to estimate ozone levels in areas without direct measurements, particularly rural regions.

The team then calculated health impacts using data on ozone exposure, population density, and life expectancy.

This isn't the team's first look at wildfire health risks. A 2023 study published in The Lancet Planetary Health examined black carbon, a soot-like pollutant tied to heart and lung disease. Wang believes ozone poses the greater overall threat.

“While there are regional differences, in general the impact of surface ozone is always bigger than black carbon,” Wang said.

What This Means for Iowa

The takeaway for Iowans is clear. No matter how tight local regulations get or how much the state reduces its own emissions, wildfire smoke from western states and Canada can still degrade the air quality here. The current regulatory system was not designed for this reality.

As large fires continue burning across the country and fire seasons grow longer, the problem will keep getting worse unless the federal government rethinks how it regulates air quality in an era of transboundary pollution.