Coronavirus Pandemic: Bay Area air pollution sees dramatic 24-hour drop on 10th day of shelter-in-place

SAN FRANCISCO (KGO) -- If you're leaving the house on one of those state-sanctioned walks around the block, you can breathe a little easier.

Air quality around the Bay Area was exceptionally good Thursday, as streets and highways around the region were practically empty amid the novel coronavirus pandemic.

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The Air Quality Index, or AQI, dropped into the single digits in parts of the North Bay and South Bay. (Any AQI score between 0 and 50 is considered "good" by the Bay Area Air Quality Management District.)

AQI scores were recorded at nine in Napa, eight in Vallejo, and nine in San Martin (a drop from 39, 37 and 34, respectively, on Wednesday). Those were the lowest scores recorded in the Bay Area Thursday.

In San Francisco, the AQI was 19 Thursday (a drop from 37 just one day earlier). In West Oakland, the AQI dropped 24 points in 24 hours, from 37 to 13.

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The major drop in traffic has a lot to do with the cleaner air we've been breathing since Bay Area counties (and eventually the entire state) were put under a shelter-in-place order. Six Bay Area counties enacted shelter in place restrictions starting March 17, followed by the remaining three counties a few days later.

But the sharp decline in commuters is not the only factor at play - and not the reason we saw such a steep drop in AQI over the past 24 hours.

"We've had really unsettled weather. That includes rain and wind, and that helps really clean out the pollution," said Kristine Roselius, a spokesperson for the BAAQMD. "The other thing is a dramatic drop in traffic. It's taken our No. 1 contributor of air pollution in the Bay Area out of the mix."

While it's too soon to evaluate just how much our air quality has improved since shelter in place orders took effect, Roselius said the BAAQMD did a "back of the envelope" estimate on what the impact of a 70% reduction in traffic would be on three types of pollutants. They estimate such a dramatic decline in cars on the road would reduce fine particulates in the air by 20%, ozone smog by 38% and carbon dioxide emissions by 26%.

At a time when almost everyone is concerned with respiratory health, Roselius said the good air quality is helpful for those who have respiratory conditions.

"There's not much bright sides these days, but this is one of them."

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