Clovis is San Joaquin Valley’s worst area for ozone

Clovis emerged this year as the worst ozone trap in the San Joaquin Valley. In fact, Clovis finished third-worst in the country.

The ozone exceeded the federal health threshold 56 times this year in Clovis. That’s not a record for the city, which had 92 in 2001.

Though Clovis is usually a dirty-air hot spot, I can’t remember the last time it led the Valley. I quickly scanned the years and saw Clovis had the most in 1997.

Several years ago, Arvin was usually the worst place. If you look closely at the statistics, you see the longtime Arvin monitor was moved about 2010 by the state.

Activists have since been suspicious that Arvin suddenly had fewer instances of exceeding the threshold. Local air officials have studied the region with mobile monitors and concluded the air actually has cleaned up.

So in the last few years, the worst place has been mostly Sequoia National Park. The Sequoia air monitor at the Ash Mountain entrance is just the right elevation in the foothills to get a steady diet of pollutants rising from the Valley.

What about Clovis? I’m told it’s probably just little changes in a dynamic that’s been going on for a long time in the Valley. It’s called the Fresno eddy, a breeze that circulates counterclockwise, picking up pollutants and returning dirty-air plumes to various places in the regions.

The worst place in the country is Crestline, a community in the San Bernardino Mountains. Again, it’s not the traffic that makes Crestline the biggest loser. It’s the location downwind of Southern California freeways.

Crestline exceeded the federal eight-hour standard 70 times this year. The second-worst was at Redlands, also in San Bernardino County, with 57.

You don’t see numbers from other cities around the country on the list. That’s because no city has numbers that even approach California. The Valley and Southern California are the heart of the country’s ozone problems.

By the way, the highest peak of ozone this year in the Valley was at Sierra Skypark in northwest Fresno. The reading was 125 parts per billion, which is one shy of exceeding the old one-hour federal ozone standard.

It happened between 3 and 4 p.m. on Sept. 12.

This story was originally published October 23, 2014 at 8:36 PM with the headline "Clovis is San Joaquin Valley’s worst area for ozone."