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Southern California’s first heat wave of the season is going to lead to increased air pollution over the holiday weekend, and fireworks will also contribute, experts say.

A high-pressure system over the Southland will push temperatures into the upper 90s and triple digits in the inland valleys and deserts Friday through Monday, according to the National Weather Service.

Scott Epstein, program supervisor with the South Coast Air Quality Management District, says the hot weather is the first of two factors colliding to produce poor air quality.

Los Angeles Smog
Century City is seen through the smog from a camera in downtown Los Angeles on June 30, 2023. (KTLA)

“With heat in the summer, we get a lot of smog pollution,” Epstein told KTLA Friday. “You get a lot more evaporation of emissions, and the reactions in the atmosphere that form ozone happen faster when temperatures are higher.”

Epstein is expecting air pollution to reach unhealthy levels over the next several days, particularly in the afternoons.

Then, once temperatures begin to cool on Tuesday, smoke from fireworks will deliver yet another round of particulate pollution.

“It usually starts around nightfall on the Fourth of July and can last until the afternoon on the fifth,” says Epstein. “Pretty much every year we get high particulate pollution on Independence Day. Some years are better than others, but all years are bad.”

As expected, air quality was beginning to deteriorate in the Los Angeles area early Friday afternoon.

AQMD’s real-time map shows yellow, or “moderate,” readings for most of the region, and orange pollution levels considered “unhealthy for sensitive groups” in the Inland Empire and Santa Clarita Valley.

Southern California Air Pollution Map
Air Quality Index readings in Southern California on the afternoon of June 30, 2023. Yellow is considered “moderate,” and orange is considered “unhealthy for sensitive groups.” (South Coast AQMD)

People with respiratory issues or heart disease are encouraged to stay indoors when the Air Quality Index is orange. Epstein believes some parts of the Southland could see air pollution fall into the red category over the weekend, which is considered unhealthy for everyone.

For those who want to exercise despite the conditions, Epstein recommends starting early.

“Air pollution tends to be worse in the afternoon, so getting exercise in the morning is probably best and it’s also cooler and more comfortable then.”

Residents are encouraged to to download South Coast AQMD’s mobile app for iOS and Android to receive real-time air quality alerts and weather information.