WASHINGTON – The Environmental Protection Agency’s decision to allow the sale of gasoline with higher ethanol content in Arizona during May is intended to offset price hikes related to the Iran war.
But there’s a reason why the EPA has prohibited that blend in the summer months since 2011: the hotter the temperature, the more ground-level ozone is generated as cars burn that fuel.
E15 is gasoline blended with 15% ethanol, much of which is produced from corn.
“Because ethanol can increase gasoline volatility even at low levels, E15 can evaporate more easily in higher summer temperatures and create ozone,” J.W. Glass, senior EPA policy specialist at the Center for Biological Diversity, said by email.
Typically, E15 is sold in Arizona from September to June 1, although suppliers start to transition from the winter blend in April. The rest of the year, gas that isn’t blended with ethanol is used, reducing evaporation in hotter weather and along with it, the risk of smog.
In 2025, EPA issued a series of 20-day waivers allowing retail E15 sales from May 1 to Sept. 15 when they would otherwise have been banned. EPA administrator Lee Zeldin’s announcement before the initial waiver indicated that he intended to allow year-round sales.
On March 18, Gov. Katie Hobbs, a Democrat, asked the EPA to delay the mandatory annual transition to summer blends, citing rising fuel prices stemming from the war with Iran.
A week later, Zeldin issued an emergency waiver allowing E15 sales nationwide through May 20, and indicated he may issue more 20-day extensions later – the most allowed by law.
“The price of gas has skyrocketed due to the war in Iran,” Hobbs posted after the EPA announcement. “This important waiver will help create supply certainty, bring prices down and help Arizonans get by.”
Zeldin didn’t indicate whether he intended to make the 2026 waiver year-round. But in the same announcement, Agriculture Secretary Brooke Rollins said that “year-round E-15 is essential for the farm economy, and Congress needs to find a common sense solution that provides much needed certainty to consumers and farmers.”
Last year, the EPA renewed waivers repeatedly, ultimately allowing E15 sales in Arizona through Sept. 15.
Health experts say the use of E15 puts air quality at risk, and warn that increases in ground-level ozone can be disastrous for people with asthma and other health conditions.
“There’s a direct relationship between ozone and fine particulate matter exposure and deaths,” said Dr. Jamie Garfield, a national medical spokesperson for the American Lung Association. “People who have chronic respiratory, chronic pulmonary or chronic cardiac diseases are more likely to have an exacerbation when they are in locations that have high air pollution and ozone pollution.”
The association’s 2025 State of the Air report, which documents pollution from fine particulate matter and ozone – a combination known as smog – ranked the Phoenix metro area fourth nationwide for ozone.
According to the study, Phoenix residents endured 55 days of unhealthy air in 2025, a seven-day increase from the previous year.
State officials say the brief extension of E15 sales will have little public health impact.
Shea Sorenson, deputy public information officer for air quality at the Arizona Department of Environmental Quality, said recent testing that compared E15 to the 10% blend usually sold in the summer found no noticeable differences as far as ozone.
“The analysis showed that switching to E15 would cause a negligible increase in ozone-forming pollutants – roughly 0.04%, or 12 pounds per day across the entire region,” she said. “Because the difference is so small and the waivers are temporary, ADEQ does not expect E15 to have a meaningful or lasting impact on Arizona’s long-term air quality goals.”
Sen. Ruben Gallego, a Democrat who has been highly critical of Trump’s attack on Iran, which disrupted global oil supplies, also praised the EPA’s move and predicted it “will help lower gas prices and bring some relief to Arizona families.”
But environmentalists say they’re worried about the immediate effects on public health and the precedent.
Since 1972, Arizona’s State Implementation Plan has been used to manage the state’s air pollution through revisions, ordinances and rules that are approved by the EPA. These rules are based on the Clean Air Act, and measure six air pollutants, including ozone.
While the SIP does not allow the sale of E15 blends in the summer months, the EPA has issued waivers every year since 2022 to allow the gas to be sold into the summer months in Arizona.
“Historically, EPA has not focused on smog impacts of the cumulative public health burden, despite its obligation to do so,” Glass said in an email. “Increased temperatures and increased consumption of E15 means increased smog. Increased smog means increased lung problems, but also harm to the natural environment, damage to vegetation, and even disruption of important pollinators like bees and butterflies.”
The link between heat and ozone is well-established. It’s called a “climate penalty factor.”
A study published in December by University of Arizona researchers found that ozone levels were twice as likely to exceed federal standards in Phoenix during a heat wave – four straight days at 111 degrees or higher – as on other days. The study looked at 11 summers from 2011 to 2022 and found exceedances on 20% of days during heat waves.
“As heat waves become more frequent and intense with climate change, ozone pollution may worsen in cities like Phoenix,” the study’s lead author, Lakshmi Parakkat, a UofA graduate student who studies climate change and aerosols, said by email.
In Arizona, 80% of ground-level ozone comes from natural sources such as wildfires, plus pollution from outside the state, according to the Maricopa Association of Governments and others.
“Yuma is heavily impacted by ozone transport from California and Mexico,” Karen Peters, director of ADEQ, testified to the U.S. Senate Environment and Public Works Committee in March 2023.
But local reductions in emissions do help control local air quality.
As of April 13, the average price per gallon of regular gasoline in Arizona was $4.70, up from $4.10 one month earlier, though down 4 cents from a week ago, according to data from AAA.
Nationwide, the average was $4.12 per gallon, according to AAA. Until April 2, that average hadn’t hit $4 in nearly four years.
Some economists expressed skepticism about the Trump administration’s effort to drive down prices at the pump by extending E15 availability.
Kenneth Gillingham, a professor of environmental and energy economics at Yale University, agreed that keeping E15 on the market could cut gas prices by 20 cents per gallon but noted that “does not account for any impacts on the environment or human health.”
“Ethanol is actually worse in terms of local air pollutants than gasoline,” he said. “It also does not account for the fact that ethanol is less energy dense, so using a blend with a higher fraction of ethanol reduces your fuel economy by a few percent. This would reduce the actual savings on fuel.”
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