North Bay makes gains in air quality as residents stay at home during coronavirus pandemic

Major declines in the daily commute and weekend car trips as residents stay home to slow the spread of coronavirus have resulted in cleaner air in the North Bay, a silver lining in the week-old shelter-in-place order.

Air quality gauges across the Bay Area and around the world are measuring well-below average levels of vehicle emissions, including smog-producing greenhouse gases like ozone, carbon dioxide and nitrogen. The amount of tiny particles spewed by cars into the atmosphere is also down, compared to the typical weekday.

Each of these contributors to air pollution have declined significantly at Bay Area Air Quality Management District sensors in Sebastopol, Napa, San Rafael and Vallejo. As a result, skies have appeared clearer between recent weather systems that make it difficult to accurately assess sudden changes in air quality, said Kristine Roselius, a spokeswoman for the region's air district.

“We're seeing low numbers everywhere,” Roselius said. “The No. 1 source of pollution in the Bay Area is traffic, so if you're taking a significant portion of that traffic off the roads, that's why we're seeing these reductions, we believe.”

Daily vehicle counts on the Bay Area's eight bridges have plummeted since the majority of its nine counties initiated the stay-at-home mandate March 17. One day later, Sonoma County joined the group with its own restriction to help slow the spread of the coronavirus, which causes a respiratory disease known as COVID-19.

During the last three days of the workweek, the number of crossings over the Richmond-San Rafael Bridge was cut nearly in half compared to the prior year, according to the Bay Area Toll Authority. Over the weekend, counts continued to fall, with the link to the East Bay carrying on Sunday roughly a third of its usual total traffic.

“We are in a totally unprecedented situation here in terms of this hasn't been a slow decline in activity; it's just fallen off the cliff,” said John Goodwin, spokesman for the regional toll authority. “It is a small silver lining to this gray cloud of COVID-19.”

The vehicle drop-off has been even sharper over the Golden Gate Bridge. Following the local shelter-in-place order, the iconic span between the North Bay and San Francisco saw an average of about 38,000 vehicles each day, or less than a third of the typical workday.

“This is good news in that it means people are heeding the shelter-in-place orders and staying home, only using the bridge and transit for those essential trips that are allowed,” said Paolo Cosulich-Schwartz, a Golden Gate Bridge District spokesman. “Largely, people are staying home and we're happy about that.”

Descartes Labs, a geospatial analysis firm in New Mexico, is seeing similar trends in the region, based on its review of smartphone location data to understand changes in mobility during the pandemic.

The distances that drivers traveled in Sonoma, Lake and Mendocino counties nosedived late last week and into the weekend. On the first two days of the shelter-in-place rules, travel in Sonoma County plummeted more than 75% from normal levels - the 13th largest reduction in travel in the state, according to cellphone GPS data tracked by Descartes Labs. Travel tumbled 50% in Mendocino County and 70% in Lake County during the same period, although the sample size was much smaller in both counties, decreasing the precision of the measurement.

Pollution data suggests vehicle traffic declined about 70% across the Bay Area, the region's air district estimates. A drop of that magnitude would cut carbon dioxide emissions by more than a quarter and nitrogen in the air we breathe by almost 40%, Roselius said, in addition to an estimated 20% drop in fine particulate matter produced by cars.

“Yes, it is significant,” she said, while noting the gains are likely temporary. “How to tease out long-term trends and things like that, that remains to be seen.”

Sonoma County Supervisor Shirlee Zane, a board member for the regional air district, said she was hopeful the temporary stay-at-home order would lead to permanent changes in commuters' habits. She said people should rethink the way they use cars by reducing solo trips and increasing the use of carpools and mass transit, which would help county efforts to reach state benchmarks for cutting greenhouse gas emissions.

“When the pandemic does subside and we see a tremendous reduction of cases of coronavirus or a vaccine is created, will we take a page out of this moment in history and say, ‘Hey, we learned something through all of this?' ” Zane said. “We have to find a way to retain some of what we're enjoying right now, with cleaner air and the benefits.”