Earth Log

Surprisingly, no problem with dirty-air standards on Fourth

I’ve got two things you might want to know about the last few days — one is regular summer stuff with just a twist, the other might surprise you.

Regular stuff with a twist: Fresno’s run of 100-degree days ended at eight on  Monday, though the triple digits came right back. The twist was the clouds and the little bump in humidity.

Fresno does not get a lot of overcast July days that snap 100-degree streaks. It was monsoonal moisture from Mexico and Arizona, according to the National Weather Service. The pattern often happens in August, but it also appears in July sometimes.

In case you’re wondering, the record for consecutive 100-degree days in Fresno is 21, set in 2005.

Now for the possible surprise: The air in the San Joaquin Valley wasn’t dirty enough to exceed federal standards on the Fourth of July. The ozone didn’t build up beyond the threshold and neither did particulate matter from the fireworks displays.

It may also surprise you to know the Valley had a small streak of clean Independence Days from 2009 through 2010. Then from 2011 through 2013, the ozone problems came back on the Fourth of July.

This year, Clovis and Turlock came close to exceeding the eight-hour standard for ozone, but stopped short. And apparently tiny particles in the smoke from fireworks did not cause an exceedance anywhere in the Valley.

I’m not saying there were no spikes of the fireworks particles. Fresno, Bakersfield, Turlock and Stockton showed some pretty big jumps in pollution in the evening.

In Fresno, the spike hit 107 micrograms per cubic meter of air between 8 p.m. and 9 p.m. The standard is a day-long average of 35 — the average in Fresno was 19.3 on the Fourth, well below the threshold.

One meteorologist told me it’s possible the light breezes on the Fourth helped to keep the air clearer. As for ozone, the rush-hour traffic is usually a lot lighter on holidays, so maybe it helped, too.