The 25 Most Polluted Cities in the US

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Visalia-Porterville, CA

  • High ozone days per year: 101
  • No. of days with unhealthy particle pollution: 6
  • People with asthma: 34,070
  • Population: 464,493

Nestled beside State Highway 99 – a busy truck thoroughfare – the towns of Visalia and Porterville have the worst air pollution of any other area in California’s Central Valley. The virtually year-round sunny skies further contribute to the formation of ozone.

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