The U.S. Environmental Protection Agency announced Thursday that it wants to reclassify the region encompassing Denver and the northern Front Range as a “serious” violator of federal health standards after ozone levels failed to meet air quality standards.

The move, which will require public comment, was expected as Gov. Jared Polis earlier this year directed state air officials to not pursue an exemption that would have reduced Colorado’s responsibility under the federal Clean Air Act.

The Denver region has been classified as a “moderate” violator of ozone standards since 2016. That region, as classified by the EPA, includes Denver, Greeley, Fort Collins and Loveland.

“We recognize how vital it is for the department to act and assertively reduce ozone pollution in the Denver Metro/North Front Range area — as well as throughout Colorado,” said Jill Hunsaker Ryan, executive director of the state health department, in a statement.

“With the backing of the state legislature and governor, we are moving forward on developing strategies to reduce emissions from oil and gas facilities, electrify the vehicle fleet and look for other ways to reduce pollutants that cause ozone.”

The EPA is making its decision to reclassify the Denver area based on air quality data collected between 2015 and 2017. The new designation will require new measures to be implemented to reduce emissions, according to a news release.

When Polis opted to forgo an exemption, he ordered work to reduce pollution in the state through measures that include using electric vehicles, adopting renewable energy and reducing oil and gas emissions.

Polis, in a statement, said his administration didn’t seek the exemption because it was time “to stop sugar-coating the bad state of our air quality.”

“Seniors and kids have been affected the most by our smog this summer,” he said. “Moving to ‘serious’ status finally helps us stop sweeping our air quality crisis under the rug and gives us additional tools to move urgently to make our air cleaner.”

The move comes as air quality in the Front Range has worsened in recent years, including as oil and gas companies have expanded in Colorado, causing ozone readings to exceed the 2008 health standards.

Other sources of ozone air pollution include cars and pollution from other states and countries. In Colorado, some air pollution has come from China, possibly from coal-burning power plants.

Ozone affects lung tissue and can aggravate diseases such as asthma and chronic bronchitis, and it can cause chronic obstructive pulmonary disease, according to the EPA.

“EPA is proposing this action as required by the Clean Air Act,” said Gregory Sopkin, EPA Regional Administrator, in a statement. “We will continue to support the state as they revise plans and implement new measures that will reduce ozone-forming emissions across the many sources contributing to air quality impairment along Colorado’s Front Range.”

The agency will be accepting public comments on the proposal for 30 days starting Aug. 15. It will also hold a public hearing at its office in Denver on Sept. 6, the news release said.