The view of the Richmond-San Rafael bridge is partially obscured by hazy smoke-filled air in June 2008, when Northern California suffered from numerous wildfires. (Justin Sullivan/Getty Images)
Jenny Wread is one of several KQED listeners who wanted to know more about air quality in the Bay Area.
Last summer, she was commuting regularly between Marin and the East Bay and noticed a lot of smog.
So she contacted Bay Curious, and we met up for a stroll in Berkeley recently.
"Look at the trees," she said. "They don’t look green. It’s like looking through a dirty window. Everything's gray!"
Wread's hypothesis: "My guess is that there’s just a lot more cars on the road and the air quality has gotten worse."
How do we measure air quality?
We took Wread's concern to the experts. The Bay Area Air Quality Management District is the agency that monitors our air. Eric Stevenson oversees the agency's monitoring network of 35 stations. He says there's at least one station in each Bay Area county.
The measuring posts are in city centers and rural spots, to get a range of data. Stevenson says there are also monitoring stations near industrial pollution sources like refineries, power plants and ports.
The stations can look like mini trailers by the side of the road or probes on the tops of buildings. They're made to be pretty unobtrusive.
They're continually taking measurements of various pollutants. The Environmental Protection Agency requires monitoring of six so-called criteria pollutants: carbon monoxide, lead, ozone, particulate matter, nitrogen dioxide and sulfur dioxide.
The two most harmful to human health are ozone and particulate matter called PM2.5 (which includes all particulate matter 2.5 micrometers or smaller).
Ozone comes from cars, power plants and refineries, when emissions react with sunlight. It's a bigger problem in the summer.
Particulate matter comes from emissions and from burning things. It could originate from industrial sources like a power plant or even a cozy fire in your fireplace. Particulate matter is more of a wintertime concern.
When we talk about air quality, we’re talking about concentrations of these pollutants.
How dirty is it?
It turns out that the air in the Bay Area is among the cleanest in the nation for a metropolitan area of its size.
Stevenson at BAAQMD says air pollution in the Bay Area has been decreasing over time, and is way down since the 1960s.
Stevenson said the biggest reason for the improvement is stricter regulations on emissions from cars and industrial sources.
"The California Air Resources Board has authority over cars and they set very strict limits," he said. "Cars now are significantly cleaner than the '70s and '80s. That has really helped improve air quality."
The Clean Air Act allows California to set stricter standards than the federal government on emissions from cars. Good to note: The state needs a waiver from the EPA to set the stricter threshold, and different administrations have differed on whether to allow it. Some are worried that it may be halted under a Trump administration.
What about Spare the Air alerts?
Wread was convinced the air was dirtier in the Bay Area because she was hearing more Spare the Air alerts. The air district issues alerts when it appears that pollution levels will exceed national standards for safety. The idea is to get people to drive less and not put more pollution into the air by, say, burning stuff. KQED and other stations broadcast these alerts as a public service.
Does that necessarily mean that air quality is worse? It turns out, no. And here's why.
The Air Quality Management District says the actual reason there are more Spare the Air alerts now is because in 2015 the Environmental Protection Agency tightened the standards for ozone levels from 75 parts per billion to 70 parts per billion. The air district had to call more alerts to meet the new standard.
So while Wread’s logic was sound, the data she was using had shifted.
While air quality has improved overall in the Bay Area, not everyone is breathing the same air.
West Oakland and Bayview-Hunters Point in San Francisco are two hot spots that are more polluted because they're near major sources of pollution like ports and freeways.
John Balmes of UC San Francisco and UC Berkeley says neighborhoods that are more polluted often have some things in common.
"They tend to be in communities of color with lower socioeconomic status where there’s lots of stuff going on, typically more freeways, power plants, refineries and other kinds of transportation corridors," he says.
Balmes says these communities are at greater risk for health problems like asthma and heart conditions.
Despite this inequity, there is a silver lining. All over the Bay Area, air quality is getting better. Balmes says that partly we can thank stricter rules on heavy-duty diesel trucks that often operate near industrial sources.
“There’s still a disparity," he says, "But everywhere has gotten better."
What about L.A.?
Whether it's a baseball game or good food or average ozone levels, Bay Area locals love to beat L.A.
So, how does our air compare? Well, L.A. is, literally, the worst.
But, bragging rights might not really be earned here, because Stevenson says a lot of it has to do with factors beyond our control.
"The L.A. basin is kind of a bowl," he says. "And it’s hot and so that forms ozone. We can’t blame it all on them. They would have these problems even if people didn’t live there.”
The Bay Area, on the other hand, is pretty fortunate when it comes to how topography affects air quality. Strong winds called prevailing westerlies push dirty air east all the way to the Sierra. Many argue that pollution from the Bay Area (and maybe Asia) contributes to poor air quality in the inland San Joaquin Valley.
So, for now Bay Area residents, you can breathe a sigh of relief and know it was a relatively clean one.
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