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.