9. San Jose – San Francisco – Oakland, CA
The air quality in this metro area is one of the worst – these cities moved from 33th to 4th position in particle-pollution; however, they made a small improvement in ozone pollution (from the 16th to 18th position) over the last year. There’s still a lot to be done regarding air pollution in this area since more than 8.71 million people are breathing it.
stellamc/Shutterstock.com
