Sheltering in Place Has Vastly Improved Region’s Air Quality—But How Long Will It Last?

Amidst the dreariness of life under quarantine, San Jose State professor Eugene Cordero has found a silver lining in the Bay Area’s clear blue skies.

Cordero, a professor in San Jose State’s department of meteorology and climate science, has been measuring Bay Area air quality from the roof of the university’s Duncan Hall.  His recent findings on the concentrations of black carbon aerosol, a type of emission that comes from cars and factories, offer an encouraging picture of how shelter-in-place has benefited the local environment.

“It’s more than a 50 percent reduction, so that’s pretty significant,” Cordero said.

Granted, Bay Area air quality is often in flux, he added, so such a drastic reduction in particulate matter can also happen when a poor-air-quality day precedes rain. However, in this case, Cordero said he sees a connection between the clearing of the roads and the clearing of the skies. “This is not unprecedented,” he said in a recent interview, “but certainly the reduction in traffic is unprecedented.”

As sheltering in place has forced many regular commuters to work from home, roads and freeways have opened up, drastically reducing traffic even during the Bay Area’s typically congested morning and evening rush hours.

Dr. Thomas Dailey, chief of pulmonary medicine at Kaiser Permanente in Santa Clara, said the dramatically improved air quality has had many positive ramifications for cardiovascular health among his patient population.

“What we’re seeing is far less particulate matter, far less ozone, less nitrogen dioxide, less carbon monoxide, less sulphur dioxide and it appears to have potentially very positive health benefits,” he said.

Dailey also served for nine years as chair of the hearing board for the Bay Area Air Quality Management District.

The most immediate benefits can be seen in people who normally experience pulmonary and cardiovascular symptoms due to preexisting conditions such as asthma and emphysema. Dailey also stated that children—who are normally at higher risk for pulmonary complications when air quality is bad—will also fare better now that the air quality has improved. “We know when there are air quality problems, when there are fires, when we have ‘Spare-the-Air’ days, there’s increased admissions in hospitals for asthma, there’s increased heart attacks and strokes, increased exacerbations with patients with emphysema and COPD,” Dailey said.

As long as people can maintain social distancing, Dailey said, the cleaner air presents an opportunity for all people, but especially for those with lung conditions. He encourages people to get outside and take advantage of the fresh air, stressing the importance of exercise to pulmonary health. “Exercise is a key component of the management of asthma emphysema, COPD,” he said.

Masks—now required in most Bay Area counties—can also help mitigate the effects of pollen for allergy sufferers who wish to take advantage of the clean air, he added.

Though the newly clear air is a positive side effect of quarantine, when the slowdown is over and traffic gridlock returns, so too will the smog.

“I think a lot of what we’re seeing locally with air quality would have to be due to transportation, to reducing just the miles driven,” said Patrick Brown, a professor in SJSU’s department of meteorology and climate science.

While many would like to think this change in the air quality will also affect our total carbon footprint and our impact on global warming, Brown said that this is a drop in the bucket compared to global carbon emissions.

The improved air quality will not have any lasting impact on global warming or the well-mixed greenhouse gasses that accumulate in the atmosphere, Brown said. But this moment does present an opportunity for the Bay Area to confront the main cause of local pollution and change the way the region commutes.

“That kind of shows us what it would look like if we had a transportation system that was more electric vehicles,” he said. “That would be one takeaway, that if we could change our transportation fleet from internal combustion engine cars that burn gasoline towards electric vehicles then we could have this type of air quality all the time essentially.”

Since the Bay Area’s energy grid uses wind and solar to generate energy, most of the region’s emissions come from transportation. This creates a unique opportunity for the nine-county vicinity. Unlike areas of the Central Valley where most emissions are due to agricultural practices, the Bay Area has the potential to change transportation, either by improving mass transit or by moving towards electric vehicles, either of which could be fueled by renewable energy.

“This is actually good evidence, showing how we reduce or minimize things that we do daily that make an impact,” said SJSU professor Sen Chiao, who chairs the Department of Meteorology and Climate Science at San Jose State University.

“Everyone understands weather,” he said. “Today’s weather is tomorrow’s climate.”

Chiao’s maxim that “today’s weather is tomorrow’s climate” explains his strategy for analyzing, interpreting and educating about global warming and climate change.

“‘Global warming’ and ‘climate change’ do not necessarily have a one-to-one relationship,” he explained.

Global warming, while understood to be a scientific descriptor, is something that citizens in general do not often see on a daily basis. Climate change, however, can be seen and measured even on a local scale.

During the first several weeks of shelter-in-place, while Cordero was seeing a drastic reduction in emissions from cars, Chiao saw evidence of a spike in a certain pollutant that is specifically generated by burning wood.

While quarantined at home, though Bay Area citizens were not driving emissions into the atmosphere by commuting, they were using wood-burning fireplaces or fire pits. Wood-burning fires are illegal in several cities and counties in the Bay.

“People just need to buy in,” Chiao said.

Cordero said he has been “exploring education as a mitigation strategy” in terms of carbon emissions. A study Cordero performed years ago involving San Jose State students showed that education can lead to a long-term reduction in carbon emissions.

“When there are big changes in our society, those are times when we are more open to changes,” said Cordero.

He also said he would like to see more funding devoted to transportation and education, as well as increased investment in finding solutions to the livability of Bay Area cities and housing and homelessness.

“I think that mostly, though, we’re going to be focused on trying to grow our economy again,” he said. “But maybe we can grow it with some awareness that just growing the economy is not the only piece we should be focused on.”


  1. The author forgot to report the part about how this cleaner air is negatively and disproportionately impacting people of color and the underserved communities.

  2. Hopefully, companies will see the value of employees working from home and have them continue that practice.

  3. Without all that particulate mater floating around in the air, rain will stop forming and we will go into an extreme drought and everything will die.

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