Tuesday, Jul. 01, 2008

Smoky, unhealthy air could return to valley by weekend

Wind taking it away this week,

The forecast calls for blue skies in the Northern San Joaquin Valley through the Fourth of July, but the thick smoke that hung over the region last week could return by the weekend.

The wildfires in the Sierra and coastal mountains are producing the smoke, but wind flows at 6,000 feet and above are taking it away from the valley. At the same time, the delta breezes are pumping fresh air into the region.

After reaching record levels Friday, the air pollution wasn't as bad as feared Saturday and Sunday. But by the end of this week, a low-pressure area will fade and high pressure will move back over the area, said Cynthia Palmer, a meteorologist for the National Weather Service.

"More toward the weekend, we could see that smoke moving down into our area," she said.

Warmer weather is expected then, with temperatures flirting with 100 degrees Saturday and Sunday.

Valley air quality officials are keeping an eye on a new fire in eastern Kern County and the 40,000-acre blaze near Big Sur. Smoke from the Big Sur fire could drift into the Northern San Joaquin Valley this week, officials said.

The Modesto area had some of the highest air pollution readings on record last week, according to the San Joaquin Valley Air Pollution Control District.

A monitor in Turlock recorded data translating into an air quality index of 182 for fine soot particles. The real-time data still is being analyzed, but if it stands, it tops the previous high of 176 in Modesto on Dec. 20, 1999.

The district has monitored for the so-called PM 2.5 particle pollution since 1999. In the past, high particle readings were caused by residential fireplaces in the winter months before the district put restrictions on wood burning, said Shawn Ferreria, a senior air quality specialist for the district.

On Friday, Turlock had a 205 air quality index for ozone, pushing the county into the "very unhealthy" range. That reading tied for the third-highest on record. The district has access to ozone numbers dating to 1976, and the highest was a 209 AQI in 1984.

Ferreria said the bad air last week was a cumulative effect of the wildfires, light winds and natural conditions that trapped smoke in the valley. For the time being, the smoke is going elsewhere.

"As long as the upper wind flow stays out of the south, we should be safe," he said Monday.

Bee staff writer Ken Carlson can be reached at kcarlson@modbee.com or 578-2321.