LOS ANGELES — The first five months of 2026 in Southern California have been the smoggiest — with the highest number of unhealtful air days — in more than a decade, according to statewide air monitoring.

So far this year, the South Coast air basin, which includes Los Angeles, Orange, Riverside and San Bernardino counties, has seen 39 days when the concentration of lung-irritating ozone (commonly known as smog) exceeded the federal standard, according to preliminary state air quality data.

That’s even worse than the infamously hot and hazy 2017, when Greater Los Angeles had 36 unhealthful air days by June 4 and ultimately saw 145.

Many of the roughly 18 million people who live in the air basin have been subjected to unhealthful levels of ozone, a highly corrosive gas that triggers asthma attacks and a wide range of respiratory illnesses. This has taken many by surprise since successive days of smog more commonly happen in summer, when heat waves and intense sunlight convert man-made pollution into ozone.

“If we have this many violations by this time, this could be a really awful year for air quality,” said Adrian Martinez, director of Earthjustice’s Right to Zero campaign, an initiative calling for the transition away from fossil fuels. “We’re already the worst place in the country for summertime smog pollution. So it could be one of the worst years in one of the worst places in the country.”

The pollution has been especially severe in valleys. On April 18, an air monitor in Reseda in the San Fernando Valley measured the second highest spike in hourly ozone levels in the last decade.

The South Coast Air Quality Management District says the high ozone levels are due to early heat waves. Officials said they were not aware of any increase in the pollutants — most of them from different kinds of exhaust — that lead to ozone formation.

Local temperatures have been well above normal, climbing into the mid-80s and high 90s between January and April, breaking several daily high temperature records, according to the National Weather Service.

March in particular was the warmest on record in California. Riverside had an unprecedented 13 days of temperatures above 90 degrees, the weather service said.

“It was really that heat wave — conditions we typically see in July or August, we saw them in March,” said Sarah Rees, deputy executive officer of the air district. “That put us ahead of the curve in terms of how much ozone we got.”

Air district officials urged residents to monitor pollution levels on the agency’s website and mobile app, and spend only limited time outdoors when smog levels are high.

“People generally know when there’s a wildfire, because you see the smoke and smell it,” said Scott Epstein, the air district’s manager of planning and rules. “Then, it’s like, I’ve got to take precautions. Ozone, you can’t really tell.”

Southern California has been particularly susceptible to smog formation because of its millions of gas-powered cars releasing tons of tailpipe emissions each day. The region’s sunshine acts as a catalyst for smog formation. Then the mountains trap this pollution over densely populated communities.

For nearly half a century, state and local air regulators have made rules designed to alleviate this pollution, enacting the nation’s first tailpipe emission standards in 1966 and requiring catalytic converters in 1975.

Smog-forming pollution has been dramatically reduced over the last two decades, but the region still does not meet federal air quality standards for ozone.

At an air district meeting Friday in Diamond Bar, the governing board held a moment of silence for William Burke, a former longtime chair. During his tenure, the agency enacted nearly 270 rules that are credited with reducing smog-forming pollution by hundreds of tons per day. Burke, who also founded the Los Angeles Marathon, died in May at 87.

“Those are just emission reductions,” air district Chair Michael Cacciotti said at the Friday meeting. “But what it doesn’t tell you is how many kids, families, seniors were prevented from going to the hospital from an asthma attack, didn’t get cancer or other respiratory problems.”

Several residents from the Inland Empire, which suffers some of the worst smog pollution, expressed their appreciation for the air district’s efforts. But they also stressed the need for more progress.

“I’m old enough to remember growing up in the ‘70s and ‘80s ... and not being able to see the mountains for weeks and months at a time,” said Erik Morden, one of several residents who spoke at the meeting.” I know things have improved, and I want to thank all of you for all the hard work that you’re doing. But there’s a lot of invisible stuff that you don’t see, that’s still out there — a lot of particulates in the ozone and chemicals that are causing a lot of problems.”

Martinez, the Earthjustice attorney, said the abnormally early outbreak of smog should be a wake-up call to government regulators that there’s work to be done, including offering more incentives to help residents and businesses transition to zero-emission appliances.

“We shouldn’t over-complicate it. We’ve got a lot of heat, we’ve got a lot of pollution,” Martinez said. “Our contention is, this agency can’t control the weather. But the one thing it can control is the pollution.”

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