A reader asked a great question when I wrote that the Valley had ozone violations even in nice, breezy weather.

"So what does that mean? According to the AirNow website, most of the Valley stayed in the "good" or "moderate" range all day yesterday. How useful is it to be told that we have bad air, if that only applies to a few locations?"

It's a practical question. A similarly practical approach came up several years ago when folks in Stockton and Modesto realized their air quality was good compared to the rest of the Valley. They wanted to break off from the Valley air district. And, at the time, it seemed pretty sensible.

But the movement died after officials said it would require a state law to make the change. Besides, air officials said, Stockton and Modesto contribute to air quality problems in Fresno, Visalia and Bakersfield. We're all one Valley, they said. We all contribute to the problem.

Fast forward to the question at hand. The ozone violations that Arvin and Sequoia National Park had on those nice, breezy days -- when everyone else was breathing fine -- typically result from plumes of ozone-making gases that come from Fresno, Visalia and Bakersfield. Really, how much traffic and industry would you find in Sequoia and Arvin, a town of 16,000 people?

The point is that the Valley still has problems, even when it seemingly has no problems.

By the way the federal AirNow site tracks air quality for many California cities, including Stockton, Modesto, Madera, Merced, Fresno, Visalia and Bakersfield. It does not mention Arvin -- the city with the most federal ozone violations in the United States over the last dozen years.