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Are Zero-Emission Vehicles Making a Dent in California's Air Pollution?

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A public charging station for electric vehicles in the Potrero neighborhood of San Francisco. (Anne Wernikoff/KQED)

Read a transcript of this episode.

Last October, Bay Curious listener Scott Mitchell got his first electric vehicle.

It was exciting for him — not just because he got a shiny new car, but because he now felt part of the bigger social project of creating a fleet of zero-emission vehicles on the roads.

“I equate it to when we switched from horse-drawn carriages to internal combustion engine cars. It’s that big of a revolution and it’s happening,” said Mitchell, a chemist living in San Carlos.

But simultaneously, Mitchell, an outdoorsy kind of guy, says he regularly gets grossed out looking at the air quality on hot summer days. He runs a trail in the Rancho San Antonio hills near Los Altos, and says the view from the top can be brown and smoggy.


“You get to the very top of the ridge, and you’re thinking you’ll see the skyline of San José. Instead, you see this smudgy view of the city that’s kind of blurry, and just looks gross,” said Mitchell.

Mitchell wants to know just how quickly California has absorbed zero-emission cars, and whether it’s significant enough to make a tangible difference in air quality.

“We should take some pride in that and celebrate it if we’re doing good,” said Mitchell.

As far as the fossil fuel-free car trend, there’s no question there’s been exponential growth in California.

In 2010, there were fewer than 800 zero-emission consumer vehicles on California roads, according to this dashboard put out by the California Energy Commission.

By the end of last year, the number of zero-emission vehicles Californians used in their everyday lives shot up to more than 1.1 million. And that’s not even counting gasoline hybrid cars.

Not surprisingly, the counties with the highest number of zero-emission cars are the more urban ones; Los Angeles County has the most, then Orange County, then San Diego and the Bay Area counties of Santa Clara and Alameda.

Now time for a little math. There are about 29 million cars on California roads right now, and only 1.1 million of them are zero-emission vehicles. Is that enough to clean up the air?

“From a big-picture perspective, yes,” said Michael Benjamin, chief of air quality planning and science at the California Air Resources Board, or CARB, the state agency that tracks these things. “The sale of electric vehicles in California, which is increasing, is contributing to improvements in air quality that we’re seeing.”

Over the past 20 years, the air quality in the Bay Area and statewide has improved. CARB data shows a clear downward trend in the number of days where air quality has exceeded limits set by the federal Clean Air Act.

“If you ask people in Southern California who have lived there for 20 or 30 years or longer, ‘Could you see the mountains 20 years ago?,’ the answer would be no. Now it’s very common to see the mountains. And that’s a really good indicator of air pollution,” said Benjamin.

According to CARB, the improvements are in the two main kinds of pollution: ozone and particulate matter. Ozone is a main component in smog, and it can cause respiratory problems in people who live where pollution is high. Small-particle pollution comes from dust, soot and smoke.

For example, in the year 2000 in the Bay Area, there were 29 days where particle pollution exceeded standards. In 2021, there were just two days.

On average, the improvements in the Bay Area have been more significant than in the state as a whole.

When it comes to how much zero-emission cars have contributed to those air improvements, CARB says it’s hard to quantify, but in the Bay Area, it could be about 3% to 4%. Those numbers may sound low, but Benjamin says they’re sure to grow as more people phase out combustion engines.

Vehicle emissions are just one piece of a larger air-quality puzzle. There are hundreds of sources of air pollution, such as lawnmowers, factories and trucks — and they’re also much cleaner than they used to be, according to the state air resources agency.

But as usual with science, air quality is complex, and there’s a lot of variability year to year, so that downward trend in bad air days is not a straight line. With recent large wildfires in California, the number of bad air days has crept back up in certain years.

For example, in 2020 in the Bay Area, there were 25 days where particle pollution exceeded standards, and that year, according to CARB, was the worst wildfire year in California history. Those levels put us right back to the pollution we were seeing 20 years ago.

The deep, dark orange glow of thick smoke surrounds an urban skyline.
A view of the San Francisco skyline from Dolores Park in San Francisco on Sept. 9, 2020. (Beth LaBerge/KQED)

Air quality is also very much related to where we are in space on a particular day, and to meteorological conditions. The air we breathe is different if we are standing near a highway or in a park. And weather conditions such as wind, rain and sunlight affect air quality, not just sources of pollution like car exhaust.

Michael Benjamin said there is reason to celebrate ways clean air efforts have been successful, but there’s still a lot more work to do to address the inequalities people experience with pollution on a neighborhood level.

And he says wildfires, which have been getting bigger and more frequent, really put us in danger of reversing the air quality improvements we’ve made in recent decades.

“We are very happy with the improvements that we’ve seen over time in regional air pollution. But our job is only half done,” he said. “We need to transition again away from fossil fuel combustion as quickly as we can.”

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