Metro Detroit’s worst ozone year in a decade sparks Sierra Club lawsuit against EPA

At issue is how much of the ozone problem is due to wildfire smoke.
Hazy skies above Detroit as wildfire smoke blows in from Canada on July 18, 2023. Photo by Nick Hagen.

The Sierra Club has taken legal action against the U.S. Environmental Protection Agency, seeking a review of the agency’s May determination that southeast Michigan meets federal standards for ozone under the Clean Air Act.

The filings were made in the Sixth U.S. Circuit Court of Appeals under a provision allowing parties to ask federal courts to review decisions under the Clean Air Act.

EPA’s determination means the agency will not require the region to impose more stringent restrictions on polluters and other measures like vehicle emissions testing.

The group also filed a second, related petition asking the court to review EPA’s decision to allow Michigan’s Department of Environment, Energy and Great Lakes to discount ozone monitoring data for two days on June 22 at its East 7 Mile monitor in Detroit in its reporting to EPA.

EGLE argued that ozone exceedances on those days at that location were influenced by wildfire smoke and represented an “exceptional event” under Clean Air Act rules, meaning that the data should be excluded from determining whether the region met federal air quality standards. EPA agreed.

The move comes as metro Detroit experiences its worst ozone season in a decade.

“EPA’s decision to redesignate Southeast Michigan to attainment for ozone was consistent with sound science and the process outlined by the Clean Air Act,” EGLE spokesperson Hugh McDiarmid said in a statement. “EGLE’s commitment to continuing air quality improvements in Southeast Michigan and across the state has not changed.” 

But critics argue that the East 7 Mile data may be unrelated to wildfires and should have been considered in EPA’s decision. The Great Lakes Environmental Law Center, representing Sierra Club in the suit, filed a memo to EGLE in January suggesting that the agency selected the data it wanted removed to force the data below the federal air quality standards while declining to evaluate potential local emissions sources.

Leonard said this year’s provisional data from the East 7 Mile monitor shows continued ozone exceedances. The state issued its earliest-ever air quality action day due to ozone on April 15.

“We weren’t convinced that ozone pollution was actually going to be improving; we felt that there was a chance that it would remain above the standard, and that’s what we’ve seen at the East 7 Mile monitor,” GLELC Executive Director Nick Leonard told Planet Detroit. “It’s validated our concerns and convinced us that this decision by EPA was something we needed to challenge on behalf of community residents.”

Leonard said that more protective measures are needed to protect vulnerable communities.

Ozone is a lung irritant that can exacerbate asthma, a condition that disproportionately impacts Black Detroiters and causes significant sickness and death. The state’s MIEJScreen mapping tool indicates that the  East 7 Mile monitor is located in a predominantly Black, low-income, highly impacted area for environmental injustice. 

However, industry leaders are worried more air quality regulations could depress economic growth. A Michigan Manufacturing Association representative told the Detroit News that non-attainment status would amount to a “no growth policy” for the region.

EGLE will likely ask EPA to allow it to discount ozone exceedance data again in its reports to the agency, according to McDiarmid.

“EGLE expects to flag some data for possible further evaluation considering the substantial Canadian wildfire impacts we’ve experienced so far this summer,” he said. “We will not be able to determine if the wildfire smoke events have had regulatory significance relative to ozone until all data for this year’s ozone season have been collected, quality assured, and validated.”

Quality assurance and data validation for the 2023 season will happen this fall and winter. Ambient monitoring data is certified annually by May 1 of the year following data collection.

EPA has broad discretion in how to implement the Clean Air Act; it could decide to reduce the standard for ozone, as it has done multiple times since the Clean Air Act was adopted in 1972, or it may decide to disallow wildfire smoke as an exceptional event given its new prevalence.

“Michigan, as well as many other states, will be very interested in whether EPA makes changes in rules pertaining to pollutants like ozone and particulate matter in response to the wildfire situation,” McDiarmid previously told Planet Detroit.

EGLE’s request to EPA to remove metro Detroit from ozone nonattainment includes a contingency plan outlining how the agency will maintain air quality for the next 20 years. If ongoing monitoring reveals ozone levels exceeding regulatory criteria, EGLE must select and implement additional control measures within 18 months. Potential contingency measures include more stringent control technology for existing pollution sources, alternative fuel and diesel retrofit programs for fleet vehicle operations, and traffic flow and transit improvements, among a list of other items. 

Such measures would be decided in conjunction with the Southeast Michigan Council of Governments (SEMCOG) and the Michigan Department of Transportation (MDOT). According to McDiarmid, if the data shows the region exceeded ozone standards in 2023, the soonest any contingencies could come into play would be 2024.

Leonard said he had little confidence in the contingency plan’s impact, given its long timeline and open-ended requirements.

“EGLE has broad discretion in selecting from that list,” he said. “And many of those things may take a long time for EGLE to select and implement.”


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