San Joaquin Valley air pollution officials are warning residents to cut driving and car idling as they scramble to avoid violating the federal government's ozone standard next week.
The regional air district is declaring the season's first air alert beginning Monday through Wednesday.
A combination of hot weather and increased back-to-school traffic are combining to trap ozone gas in the trough-shaped valley.
Heather Heinks, an air district spokeswoman in Fresno, said valley residents have responded in a big way to previous requests by the district to reduce car idling, especially by parents picking up students from school.
"There are 1,600 schools in the San Joaquin Valley," Heinks said. "Imagine it's 3 in the afternoon, temperatures near 100 degrees, and 20 to 50 cars are idling at each school."
If a significant percentage of those motorists shut off their engines while they waited, it could make the difference, she said, between remaining within the federal standard and spiking ozone levels.
In 2010, the region became the first in the United States to be fined for failing to meet the federal deadline for reducing ozone pollution.
The valley must record three clean years in a row for the $29 million annual fine to end. In 2011 there were three exceedances of the federal 1-hour ozone standard. Last year there were two, but the air district is calling them exceptional events and may ask to have them declared invalid.
There have been no such exceedances so far this year.
The fine is being paid by an assessment on businesses and through a $12 annual vehicle registration fee for drivers from Stockton to Bakersfield.