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Tourists at the Griffith Observatory observation deck look out at the Los Angeles skyline as heavy smog shrouds the city.
Tourists at the Griffith Observatory observation deck look out at the Los Angeles skyline as heavy smog shrouds the city in California on May 31, 2015.
(Mark Ralston/AFP/Getty Images)
LA Explained: Smog
Take a deep breath and read about how bad LA smog really is.

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Gross black dust on your windowsill. Sickly yellow haze that obscures the mountains. Childhood memories of recess cancelled due to smog alerts.

You know the air here is dirty. Now learn why.

Once Upon A Time

The L.A. smog story goes a little like this: on July 8, 1943, a mysterious haze descended on the city.

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"People were having car accidents," Chip Jacobs, co-author of Smogtown: The Lung-Burning History of Pollution in Los Angeles, told LAist. "Mothers were wondering why their kids' eyes were watering. Police officers were spinning loopy."

What was this strange haze? Was it a gas attack? Smoke from factories? From some distant fire?

To solve the mystery, local officials formed the nation's first air quality regulator, the Los Angeles County Air Pollution Control District. They began looking into the problem and quickly learned that there were a lot of sources of air pollution in greater L.A.: people burning trash in their backyards, oil refineries, smudge pots (which are small, smoky fires used by citrus growers to keep trees warm at night), and factories.

But soon, a Caltech scientist figured out that cars and gasoline were largely to blame for the eye-watering, lung-searing haze.

Smog envelopes the LA skyline in 1968
A smog-shrouded view of downtown Los Angeles on October 7, 1968.
(Los Angeles Public Library archive)

What Do Cars Have To Do With It?

Car exhaust has two main components: hydrocarbons, from the gasoline, and nitrogen oxides, which are formed inside hot, internal combustion engines. Both are harmful in and of themselves, but when they float into the sunny, Southern California air, the sunlight bakes them into a new chemical: ozone, also known as smog.

Once scientists figured out what caused smog, the crackdown began: in 1967, a new state air quality agency, the Air Resources Board, was formed. It enacted tailpipe emissions standards for cars. It required catalytic converters on new models, cleaner gasoline and, at the gas pump, those little rubber boots that trap fumes from the nozzle. In 1984, smog checks began statewide. Other industries had to clean up, too: oil refineries, cement plants, power plants. And as California cleaned up its air, other states and the federal government followed.

Graph showing top 10 U.S. Cities with the worst smog.
L.A. has the worst ozone, or smog, in the country, according to the American Lung Association's 2021 State of the Air Report.
(American Lung Association)

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Bad Now Vs. Bad Then

The air is a lot cleaner now. In 2020 , we had 157 days of unhealthy air, compared to well over 200 in the late 1980s. However, 2020 tracked the highest number of unhealthy air days since 1997, even with pandemic restrictions seeing a drop in auto travel. So when it's smoggy, it's not as smoggy as it used to be.

But Los Angeles still has the worst smog in the country, according to the American Lung Association's 2021 State of the Air report. (Again, scientists call smog "ozone." But they're the same thing).

Graph showing 8-hour ozone exceedances from 1980 to 2020
Greater L.A. exceeded federal air quality standards for 157 days in 2020.
(South Coast Air Quality Management District)

Part of the problem is that it's been hot, incredibly hot. And heat speeds up the process of ozone-formation. Experts are trying to figure out whether the spate of bad air is a new trend, reversing years of steady progress.

"Is this weather, or has this become climate?" said Atwood. "We're grappling with that question basically."

What Makes Our Smog So Special?

Three reasons.

  • One, there are a lot of us, and we own a lot of cars. Angelenos own 0.54 vehicles per person, compared to 0.43 in New York City. Also, we have the busiest ports in the country, which means tens of thousands of heavy-duty diesel trucks are on our roads, and they are way dirtier than cars.
  • Two, the mountains that ring the L.A. Basin trap that pollution as it gets pushed eastwards by sea breezes.
  • And three, our climate. Nearly three out of four days in L.A. are sunny. And the L.A. Basin frequently experiences a weather pattern where a layer of warm air will sit on top of a layer of cooler air and prevent it from dispersing. That traps pollution closer to the ground. Think of it like putting a lid on a pot.

Where's The Dirtiest Air? Where's The Cleanest?

Because the wind blows smog east, towards the mountains, the air is worst there. So places like Redlands, San Bernardino and even the tiny, mountain community of Crestline have far worse air quality than coastal cities like Long Beach or Santa Monica.

But there's another factor to consider besides smog: the raw vehicle emissions that combine to make smog can also have localized health impacts. So if you live within 500 feet of a busy road or a freeway, you're in a pollution hot spot, because that's where vehicle emissions are the most concentrated. (Use this handy map made by our friends at the LA Times to figure out how close you live to a freeway.)

A semi-truck is visible in the distance from a residential backyard.
Trucks on the SR 60 Freeway drive by Anna Gallegos' backyard in Mira Loma Village, California.
(Andrew Cullen for LAist)

In the very worst places to live, like near a freeway in San Bernardino, you will be exposed to both smog and raw vehicle emissions, said Ed Avol, the head of the Environmental Health Division at the USC Keck School of Medicine.

"It's sort of like a double whammy, so you get both the local impact of being near a roadway, and you also get the accrued accumulation of pollution that's become a regional issue," he said in an interview with KPCC/LAist in April.

What Will Breathing Dirty Air Do To Me?

When you breathe in dirty air, it triggers an inflammatory response in your body. And once that happens, a lot of bad things can happen. In the short term, air pollution can cause:

  • Difficulty breathing and chest pain.
  • Increased rates of asthma.
  • Respiratory diseases like bronchitis and pneumonia.
  • Lost school or work days.
  • Doctor and hospital visits.

Over the long term, it's much worse. Kids who grow up breathing dirty air, whether it's from living near a freeway or in a smoggy area, or both, have weaker lungs that don't work as well.
"If they never get that maximum lung growth early in life, it looks like it's permanently lost," Avol said.

For older adults, air pollution can contribute to cognitive decline, memory loss and premature death. It can also exacerbate heart disease, diabetes, obesity and cause cancer. There's even research suggesting fetuses are harmed when their moms breathe dirty air.

"In a cynical, joking way, you could say we believe air pollution causes everything," Avol said.

Two cars next to each other on a highway. The tailpipe of one car looms large.
Smog-making cars on March 22, 2006 in L.A.
(David McNew/Getty Images)

How Can I Protect Myself And My Family From Bad Air?

One of the most common ways people are exposed to pollution is while driving. So when you're on the freeway, be sure to keep your windows rolled up and re-circulate the air, instead of drawing it in from the outside. Changing your air filter also helps. And new cars are more tightly sealed than older cars, keeping pollution out.

If you can, try to live at least 500 away from a freeway or busy road. If you can't, using HEPA air filters has been shown to significantly reduce indoor air pollution when the air outside is dirty. Clean that black dust, which is a combination of diesel soot and rubber dust from tire wear, off your window sills.

Outside of the home, try to walk or bike on less busy streets, to limit your exposure to vehicle exhaust. When waiting for the bus, stand back from the street corner, where pollution levels soar when vehicles accelerate from a stop. And don't exercise near busy roads during rush hour, especially in the morning, or when the air is especially bad.

You can also check the air quality every day. This South Coast Air Quality Management District map will give you a good overview of air in your area. You can also check the Purple Air network, which measures particulate matter (like soot, dust and wildfire smoke), or have a low-cost air monitor installed at your home or work.

What Do We Need To Do To Make The Air Actually Clean?

It all comes down to transportation. Cars and trucks make up nearly 90 percent of the smog-forming pollution in Southern California (not to mention they are also the largest emitters of greenhouse gases in the state), and it's because they run on gasoline and diesel.

Switching to fuels with zero tailpipe emissions, like electricity and hydrogen fuel-cells, will make a huge difference, says Will Barrett, the clean air advocacy director for the American Lung Association.

Several semi-trucks on a crowded highway
Trucks drive along Interstate 80 on February 18, 2014 in Berkeley, California.
(Justin Sullivan/Getty Images)

"We need to see more focus and urgency on the conversion of the heavy duty sector to zero emission technology," he said.

But heavy duty trucks have proven tricky, so far, to electrify, because they would require a massive battery to power them over long distances while carrying heavy loads. Also, truckers would need frequent, convenient charging stations, and that infrastructure doesn't exist yet.

California regulators, ever the clean-air optimists, are throwing cash at the program. The ports of L.A. and Long Beach, for example, have a goal of shifting their entire fleet of largely diesel trucks and equipment to zero emissions technology by 2035 -- at a cost of $14 billion. If they can figure it out, all of our lungs will benefit.

This story is part of Elemental: Covering Sustainability, a multimedia collaboration between Cronkite News, Arizona PBS, KJZZ, KPCC, Rocky Mountain PBS and PBS SoCal.

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