Earth Log

Earth Log: Another day for Valley's rare clean streak

Update: The San Joaquin Valley added to its record streak of July clean-air days on Wednesday, making eight in a row without exceeding the federal eight-hour ozone standard.

There have been 11 days without an ozone exceedance in July. I haven't looked closely yet, but I can't remember seeing more than 10 good days in any July going back to 1995.

The heat is beginning to spike again on Thursday. Ozone needs heat and sunshine to form. And it forms best on stagnant summer days.

Keep your eye on the San Joaquin Valley Air Pollution Control District real-time monitoring for your area.

Update: The July clean streak has reached seven days in the San Joaquin Valley. And that is longer than any clean streak I've found since 1995.

The ozone level hasn't exceeded the federal eight-hour standard here since July 15. 

The readings this morning have looked good in places such as Fresno. Maybe there will be an eighth clean day in a row.

Typically, July is nearly wall-to-wall with ozone readings above the federal standard.

Ozone is a corrosive gas created when oxides of nitrogen from vehicles combine in sunlight with dairy or fuel fumes containing reactive organic gases.  The gas can cause microscopic damage to the skin and lungs.

I'll let you know if we get eight in a row after today.

The San Joaquin Valley just went through a rare July, six-day streak without breaching the federal eight-hour ozone standard. 

That has happened only one other July since 1995. In 2011, there was a six-day clean streak. And there was a five-day streak in 2000.

Before I get too carried away about the current streak, I need to point out that two of those days missed exceedances by only one part per billion. Two other days missed by only three parts per billion.

Why is the streak happening? I've been told that cloud cover, mixing breezes and temperatures below 100 degrees seemed to help.

If Tuesday passes without an exceedance of the ozone standard, it will be the first seven-day streak I can find on record for July.