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The Bay Area had 218 days of lousy air in 2018

But San Francisco itself suffered just a handful outside of the wildfire crisis

Tall buildings barely visible as silhouettes through a gray haze of smoke. Photo by Justin Sullivan/Getty Images

San Franciscans appreciates the city’s architecture, ample parks, glorious views, culture, and proximity to the ocean. But one of SF’s best assets is one that most people take for granted: our excellent air quality.

Thanks largely to the same ocean breezes that bring in the fog, most people in SF rarely have to wonder about the day’s air quality.

But that all changed for a brief period in 2018 when smoke from the deadly Camp Fire resulted in the worst air quality ever recorded in SF.

Nearly a year out from the devastating wildfire and subsequent smoke particles that blanketed the Bay Area for days on end, CPAP.com compiled air quality data taken from the Environmental Protection Agency’s air pollution sensor network for all of 2018 and compared how many days in major cities saw “good” air quality (i.e., 50 or less on the 500-point Air Quality Index scale) versus cities with “bad” (i.e., scores of more than 50, indicating “moderate” or worse) air quality.

(CPAP, which stands for continuous positive airway pressure, is a company that sells treatments for sleep apnea, hence it’s named after the ventilator design commonly used by those who suffer the condition. According to the National Institute of Health, air pollution exacerbates such illnesses.)

Per the compiled numbers, San Francisco had a total of 218 days of “moderate” or worse air quality in 2018, and only 147 days designating “good” air quality.

If that sounds surprising despite the fires, that’s a wise instinct. As is often the case, when statisticians refer to San Francisco they typically refer to the larger SF census area, which, in addition to the city, includes San Mateo County, Alameda County, Marin County, and Contra Costa County.

The latter is particularly significant, since the far East Bay routinely suffers higher average temperatures and worse heatwaves, which contributes to ozone pollution. Of the less-than-pristine 2018 air days, CPAP says 62 of them were ozone related.

In that context, the data collected here is less a reflection on San Francisco and more an indicator of how climate change and rising temperatures have affected the Bay Area as a whole.

Speaking for CPAP.com, Erin Ovadal tells Curbed SF that “an average is taken from all the active sensors within that [census] area per day, and we took those averages to see overall good and bad days in a metro area.”

The means that “if a majority are within the ‘good’ range it would be classified as so, but if a majority didn’t fall into that category it would be recorded as a ‘bad day’” for the entire region, even if certain areas were of course better or worse than others.

Case in point, when asked for figures about only San Francisco County, CPAP disclosed totals showing that SF had 278 “good” air days in 2018—even with the worst air pollution crisis in recorded history in effect.

For the curious, the South Bay (here defined by the San Jose-Sunnyvale-San Jose census area) proved much healthier overall than the rest of the region but much less so than SF itself, coming in at 149 days of “moderate” or worse air last year.