In more than a dozen California counties, a little-known rule in the Clean Air Act has forgiven air pollution – not from the sky, but from the record. After wildfires flourished across North America this year, more U.S. states east of the Mississippi may use this exceptional events rule to subtract smoke from the record, if not from the air we breathe. But these exceptional events are no longer exceptional, and the requests to obscure them from air-quality records are more common.

Reporter: Molly Peterson, The California Newsroom

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