Air quality in most of Orange County remained largely unaffected Thursday by smoke from wildfires burning to the north, according to the South Coast Air Quality Management District.

The agency’s air quality map, however, also showed air that was “unhealthy for sensitive groups” spreading across the Saddleback Valley and southern Orange County in the afternoon, mainly ozone pollution.

The smog in south Orange County, as well as the smoke that lingered in parts  of Los Angeles County, were both helped along by the same phenomenon: a temperature inversion.

Warmer air acts as a kind of lid over cooler air below during such inversions, holding smog — or, in L.A. county’s case, smoke — in place close to the ground.

“Looks like you’re just getting some typical summer smog,” said the air-quality agency’s spokesman, Sam Atwood.

Still, winds flowing onshore from the south at 8 to 10 mph helped keep the smoke from the north at bay Thursday, said forecaster Stan Wasowski of the National Weather Service.

Expect about the same on Friday, said Weather Service meteorologist Brandt Maxwell.

(AP photo of plane making fire retardant drop Thursday on Morris Fire in the San Gabriel Mountains by Reed Saxon.)

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O.C. air quality mostly unaffected by smoke

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