Support for LAist comes from
Audience-funded nonprofit news
Stay Connected
Audience-funded nonprofit news
Listen

Share This

Health

LA heat waves make the air worse to breathe. Here’s why

The downtown L.A. skyline is obscured by smoggy air
Hotter temperatures also mean more smog.
(
Patrick T. Fallon
/
AFP via Getty Images
)

With our free press under threat and federal funding for public media gone, your support matters more than ever. Help keep the LAist newsroom strong, become a monthly member or increase your support today . 

No, it’s not just in your mind. The heat waves really do make the air extra gross to breathe.

That’s because high heat helps accelerate a molecular reaction in the air, resulting in the production of one of the main ingredients in smog: ozone. This reaction is why the South Coast Air Quality Management District issued an ozone advisory for much of Southern California through 8 p.m. Thursday.

How sunlight creates ozone

Southern California has constant pollution from things like cars and factories — and now wildfires — so air pollution is never a single-cause issue. But if you browse air quality maps long enough, you may notice the outside gets extra unhealthy during a heat wave.

Support for LAist comes from

You’re not seeing things. The South Coast Air Quality Management District is the air pollution agency responsible for regulating and monitoring air quality in our region, and its map measures the presence of contributors to poor air quality. Particulate matter (shown as PM 2.5 or PM10) and ground-level ozone (O3) — common pollutants — have been shown to rise when it’s hotter.

Ed Avol is a professor emeritus of USC’s Keck School of Medicine and was chief of its environmental health division. He said the pollution problem can be a photochemical one. Ultraviolet radiation from sunlight provides the energy needed to break the chemical bonds between certain gases in the air and re-connect as ozone.

“It’s sort of a double whammy because the sun is there, the solar radiation happens. But because the heat is there, it happens at a faster rate,” Avol said. “You get both those things to sort of help push it along.”

How to check your air quality
    • This South Coast Air Quality Management District map will show you the level of pollutants in your area.
    • You can also check AirNow’s fire and smoke map, which measures fine particulate matter and fire-related detections.

This compounds in the L.A. area because it has more of a chance to react with our high levels of pollution. And when we have multiple days of extreme heat, we get a “washing machine effect.” The air moves forward and back across the basin, essentially baking the L.A. area in bad air.

“The general soup sort of stays here and it just gets a little bit more congealed, a little bit thicker day by day,” Avol said.

Support for LAist comes from

What ozone does to your health

“There is a lot of evidence now on how heat and poor air quality together could have a worse impact on health than each one of them alone,” said Rima Habre, a USC associate professor of environmental health and spatial sciences.

You likely won’t notice breathing it in the short term because each person reacts differently, according to Habre.

“When you’re talking about individual people, it depends a lot on who that person is and their baseline vulnerability for things,” she said.

Ways to protect yourself
    • Stay inside: Outdoor ozone mostly doesn’t get inside buildings.
    • Run your air conditioning or air filter, but be careful you don’t use a machine that generates ozone.
    • Limit use of gas-powered lawn and garden equipment until the evening.
    • Conserve electricity by setting your A/C at a higher temperature.
    • Put off going to the gas station and using household chemical until the evening.

Ozone is a highly irritating compound to your airways and lungs. It can quickly lead to inflammation. So for example, Habre said people with cardiovascular conditions or any kind of underlying respiratory issue shouldn’t be outside when ground-level ozone is high.

Support for LAist comes from

Another factor is what happens alongside this reaction. When ozone is high, the mixture of particulate matter becomes more unhealthy, according to Habre. That could be more reactive and induce more harmful effects.

Bad air can trigger short-term issues, like an asthma attack, but it also negatively affects your health in the long term. Exposure is associated with lower lung function and lung development over time, and there’s a greater risk of other diseases.

“Like metabolic disease and cardiorespiratory disease,” Habre said. “So, it doesn’t just act immediately. People who are chronically exposed to it over long, long periods of time… we think it also affects poor lung health and development and growth of various systems.”

Updated July 8, 2025 at 2:19 PM PDT
This story was updated to reflect the heat wave for the week of June 6, 2025.
Corrected September 10, 2024 at 11:22 AM PDT
This story was updated to correct Ed Avol's title, how the ozone formation process happens and an infobox that stated wearing a mask can help protect against ozone. According to the South Coast Air Quality Management District, masks are not effective against ozone because it is a gas. LAist regrets the errors.

At LAist, we believe in journalism without censorship and the right of a free press to speak truth to those in power. Our hard-hitting watchdog reporting on local government, climate, and the ongoing housing and homelessness crisis is trustworthy, independent and freely accessible to everyone thanks to the support of readers like you.

But the game has changed: Congress voted to eliminate funding for public media across the country. Here at LAist that means a loss of $1.7 million in our budget every year. We want to assure you that despite growing threats to free press and free speech, LAist will remain a voice you know and trust. Speaking frankly, the amount of reader support we receive will help determine how strong of a newsroom we are going forward to cover the important news in our community.

We’re asking you to stand up for independent reporting that will not be silenced. With more individuals like you supporting this public service, we can continue to provide essential coverage for Southern Californians that you can’t find anywhere else. Become a monthly member today to help sustain this mission.

Thank you for your generous support and belief in the value of independent news.

Chip in now to fund your local journalism
A row of graphics payment types: Visa, MasterCard, Apple Pay and PayPal, and  below a lock with Secure Payment text to the right
(
LAist
)

Trending on LAist