ST. PAUL — Tighter federal air pollution rules aimed at reducing smog and the health risks from it could affect Minnesota.

Minnesota currently complies with the federal ozone limit of 75 parts per billion. But the Environmental Protection Agency on Wednesday proposed lowering that limit to between 65 and 70.

Ozone is formed when vehicle exhaust and other emissions mix with heat and sunlight.

Frank Kohlasch of the Minnesota Pollution Control Agency said the state’s ozone levels have been fairly stable, but the federal standards are catching up to the state.

Mike Harley of the Environmental Initiative said Minnesota has been on the edge of compliance and non-compliance for over a decade.

Minnesota’s worst ozone days usually come during the summer months, typically in the Twin Cities metro area.