Los Angeles-Long Beach-Anaheim, CA
- High ozone days per year: 137
- No. of days with unhealthy particle pollution: 13
- People with asthma: 1,004,601
- Population: 13,353,907
A notoriously smoggy area prone to thermal inversions, the Los Angeles metro area is the second most polluted in the nation. High ozone levels persist for more than a third of the year, with the warm climate contributing to ozone formation.