WASHINGTON— Two environmental groups filed a formal notice today of their intent to sue the Environmental Protection Agency for failing to find that 10 areas recently designated as in “serious” nonattainment for the Clean Air Act’s ozone standards missed deadlines to evaluate and reduce ozone pollution.

These 10 areas — together, home to more than 50 million people — include parts of the country with some of the nation’s worst air quality. Ground-level ozone — commonly known as smog — harms public health and the environment.

“Smog pollution is a deadly threat to people and our planet, but the EPA is failing to ensure that states clean it up,” said Victoria Bogdan Tejeda, a staff attorney at the Center for Biological Diversity. “The EPA’s failure to make these areas cleanup their dirty air imperils the lives of people and wildlife.”

Ozone pollution is linked to human health problems like asthma attacks and can cause premature death. Those most at risk include older adults, children and people who work outdoors. Ozone pollution also contributes to the climate crisis by hindering plant growth and reducing plants’ carbon sequestration potential.

“Too many communities in the United States are overburdened by harmful air pollution, and the EPA’s failures here make the problem worse,” said Kaya Allan, illegal toxic threats program director with the Center for Environmental Health. “We’re going to make sure that the EPA and the states do their job and address dangerous smog pollution.”

The EPA missed its deadline to issue findings that the following regions failed to submit plans to address “serious” nonattainment of Clean Air Act ozone standards: the Chicago-Naperville area of Illinois, Indiana, and Wisconsin; the Dallas-Fort Worth and Houston-Galveston-Brazoria areas of Texas; the New York City metro areas of Connecticut, New York and New Jersey; the non-metro areas of Connecticut; and San Diego County, California.