Fresno Bee Newsroom Blog

Heat, yes, but ozone needs sunlight, too

My story Sunday on cooling down Fresno to help lower ozone was directly at heat, but air temperature is not the only part of the equation.

On Sunday, nature demonstrated why heat isn’t the only factor. It was 102 degrees but just cloudy enough to slow down the chemical reaction that makes ozone.

There was no breach of either federal ozone standard on Sunday — in the middle of August with very light winds and 100-plus degrees.

Ozone needs oxides of nitrogen from combustion sources, such as your car’s engine, and reactive organic gases, such as fumes from gasoline or dairies. But without both warmth and sunlight, the gas doesn’t form as well.

Take a look at the numbers for Sunday. Fresno’s three monitors never got above 70 parts per billion for ozone. The federal eight-hour standard is 75 parts per billion, and it’s officially an exceedance when the average hits 76.

Monday looks like a similar cloudy start to the day. I saw lightning over the Sierra. If the weather stays dark and unsettled, there may be another August day in the Valley without an exceedance of the ozone standard.

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