In this Dec. 14, 2018, photo, an inversion settles over Salt Lake City. Inversions hover over Salt Lake City as cold, stagnant air settles in the bowl-shaped mountain basins, trapping tailpipe and other emissions that have no way of escaping to create a brown, murky haze the engulfs the metro area. Doctors warn that breathing the polluted air can cause lung problems and other health concerns, especially for pregnant women and people with respiratory issues. (AP Photo/Rick Bowmer)
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