Bay Area Pollution Way Down, Air District Estimates

Midday on Highway 101 in San Francisco on March 20 saw extremely light traffic. (Justin Sullivan/Getty Images)

The Bay Area’s grueling commute has all but disappeared as millions of people stay home at the order of public health officials seeking to slow the spread of this coronavirus.

As millions of cars sit parked on the street or collect dust in garages, and public transit agencies drastically reduce service, researchers with the Bay Area Air Quality Management District say there's some indication that regional air pollution is way down.

“Traffic is the top contributor to air pollution in the Bay Area,” Kristine Roselius, a spokeswoman for the agency, said in an email. “Reducing the number of cars and trucks on our roads can have a significant, positive effect on our air quality.”

Researchers at the agency took early reports estimating bridge traffic was down by 70% and used them to calculate a corresponding reduction in pollution.

The district's numbers show a potential 20% reduction in fine particulates and a 38% drop in nitrogen oxides. Carbon dioxide emissions, the leading driver of climate change, would be down 26%.

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But Roselius said the estimate is likely "conservative" and traffic could have dipped by even more, though she cautions that researchers need to see more data before they can detect an actual trend.

The Port of Oakland says shipping traffic was down 11% in March. That could also contribute to a reduction.

Of course, weather plays a major role in local air quality. A persistent low-pressure system  hovering over Southern California has kept the air crisp and clear, according to Rick Canepa, a meteorologist with the National Weather Service in Monterey.

The pressure system brought blustery, rainy conditions to the region in late March and early April, one reason for the puffy cloud formations the last few weeks.

Aclima, a San Francisco-based air quality mapping startup, says that Bay Area pollution levels have continuously  declined since March 17, when many counties initiated stay-at-home orders, according to Meg Thurlow, the company's vice president of Sensing Systems and Applied Science.

“We continue to see the same large-scale changes that we have been seeing in air pollution across a variety of pollutants, especially those associated with traffic and fossil fuel combustion,” said Thurlow. (Aclima is publishing the results in posts like this.)

This is especially true in West Oakland, a neighborhood bounded by freeways and the port.

The West Oakland Environmental Indicators Project and other advocacy groups have long noted punishing air pollution and high local asthma rates, which they say are caused by toxic diesel fumes from trucks driving in and out of the port.

Aclima is tracking a reduction in the region's carbon footprint using aggregated data from air regulators, as well as sensors, including some attached to low-emission cars.

Since 2015, Aclima has mapped air quality in West Oakland and noted higher pollution levels compared to the broader Bay Area.  Thurlow said that West Oakland's carbon dioxide levels have dropped below the Bay Area regional average during the coronavirus crisis.

She said the reduction in pollution provides "a really positive indicator to people that our actions are important with respect to air quality."

"But this is a brief reprieve when there's a lifetime of pollution disparities that have existed throughout a lot of our communities."