The Environmental Protection Agency (EPA) won’t yet say which areas of the country do not meet the Obama administration’s 2015 regulation on ozone.

The agency certified Monday that 2,646 counties, two tribal areas and five territories, or about 85 percent of the nation’s counties, meet the new standard of 70 parts per billion of ozone in ambient air, down from the previous 75 parts per billion.

But officials said they would not yet declare the areas of “nonattainment,” places that exceed the new limit, because they are “not yet prepared.”

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The EPA was required under the Clean Air Act to make all the decisions by Oct. 1.

“In the spirit of cooperative federalism, EPA will continue to work with states and the public to help areas with underlying technical issues, disputed designations, and/or insufficient information,” it said in a statement.

“Additionally, EPA modeling, state agency comments, and peer-reviewed science indicate international emissions and background ozone can contribute significantly to areas meeting attainment thresholds. The agency intends to address these areas in a separate future action.”

The designation list, for example, includes only six of California’s 58 counties. Due largely to geography, California has notoriously bad air quality and high ozone pollution.

Ozone is a component in smog, and is linked to respiratory ailments like asthma attacks. It is a byproduct of various pollutants caused by fossil fuel burning.

Opponents of the 2015 rule say it would cost billions of dollars to implement, since states would have to restrict fossil fuel use to comply.

EPA head Scott Pruitt Edward (Scott) Scott PruittJuan Williams: Swamp creature at the White House Science protections must be enforceable Conspicuous by their absence from the Republican Convention MORE sued to stop the rule in his previous job as Oklahoma’s attorney general, and he has faced numerous hurdles in implementing it.

In June, Pruitt said that he would delay the Oct. 1 deadline for attainment designations by a year.

Democratic states and environmental groups sued, and Pruitt walked back the delay.

He also missed the Oct. 1 deadline initially, causing a similar group of blue states and greens to sue.

If an area is designated as “nonattainment,” its state will eventually have to submit a plan to the EPA to improve air quality. If the state does not do so, the EPA is obligated to write a plan itself.