Weather patterns over the San Joaquin Valley trapped air pollution on the Valley floor Friday, causing elevated levels of PM 2.5 — tiny particles that can damage hearts and lungs.

It is expected to get worse into the evening Friday and then clear up Saturday, according to Jamie Holt with the San Joaquin Air Pollution Control District.

Air pollution is particularly unhealthy for children, seniors and people with existing heart and lung problems.

Sources of pollution across the region include cars and trucks, wood-burning fireplaces and industrial sources like factories, gas stations and agriculture, Holt said. Two wildfires continue to smolder in the Sierra Nevada, which also contribute to the problem.

Friday was a “no burn day,” meaning wood-burning fires in the Valley are prohibited. To report a wood-burning fire violation or to see if you are allowed to burn a fire, visit or call 1-800-SMOG-INFO.

Pollution levels were generally worse Friday in southern areas of the Valley, including Visalia and Bakersfield, though areas of Fresno were also unhealthy for sensitive groups, air quality monitors show at

“We are being squeezed between a high pressure system and a low pressure system,” Holt said.

Usually, a low pressure system allows pollution to dissipate more quickly, vertically and out of the valley, according to Holt. But the high pressure system “is basically putting a lid on the valley. It’s a lid that is holding pollution low to the ground.”

The weather Saturday and Sunday is expected to be mostly sunny and clear with calm wind, with highs in the low 60s and lows in the low 40s at night, according to the National Weather Service.

Use these tools to view real-time air quality levels in your neighborhood:

The San Joquin Valley Air Pollution Control District’ RAAN search tool provides real-time data on smog and PM 2.5 by entering an address in the search bar. You can also sign up to receive air quality alerts. The tool does not currently provide PM 10 data, which staff said may change by the end of the year.

The interactive map provides real-time data for smog, PM 2.5 and PM 10 from local monitors across the country. It is managed by the U.S. Environmental Protection Agency.

For more localized neighborhood data, use the map that compiles crowd-sourced data from private, consumer monitors. Or, use the similar that pulls data from AirVisual consumer monitors.

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