CA takes top 5 on smoggiest cities list

5 of 5: Riverside-San Bernardino is the smoggiest metropolitan area in the United States, according to a report from the environmental advocacy group, Environment California. That's based on the number of smog days per year when at least one air-quality monitor detects ozone levels above the national standard. It had 110 smog days based on data from 2010. ( Photo / KABC)

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