Finding the most polluted places in the San Francisco Bay area is simple, a new air quality analysis shows: Locate places where mostly Black, Latino, Asian and low-income residents live, and pay them a visit.
While the Environmental Protection Agency gauges an area’s air quality with fixed monitors, the new survey unearthed more granular data by sending low-emission vehicles equipped with sophisticated technology to traverse neighborhoods at least 20 times each. These forays revealed that poor people of all ethnicities experience a 30 percent higher exposure to nitrogen dioxide compared to wealthier residents, and concentrations can vary up to 800 percent from one end of a block to the next.
The painstaking examination, partly funded by the Bay Area Air Quality Management District through a $6 million contract, took more than a year. The company’s fleet traversed every city block in San Francisco, Oakland, San Jose and other municipalities to determine the true extent of pollution.
What they discovered was that the farther their mobile air monitors traveled away from the region’s more than two dozen stationary air quality monitors, the more they detected elevated levels of pollution that the fixed monitors missed. Their data questions the reliability of the system the EPA uses to surveil the air that millions of Americans breathe.
“The regulatory stationary network is not inherently designed to provide a detailed picture of air pollution at the street, community or block area level,” the analysis said.
It found that the entire Bay Area is exposed to higher levels of floating microscopic pollutants, fine particulate matter, than World Health Organization guidelines recommend. These particles, known as PM2.5, can penetrate the lungs and cause numerous respiratory diseases such as asthma.
Aclima compared its data to an international benchmark, which is far more restrictive than federal standards. The WHO sets its standard for nitrogen dioxide, NO2, at 10 micrograms per cubic meter of air compared with the EPA’s 100.
EPA limits the annual average exposure to fine particulate matter to 12 micrograms per cubic meter of air, compared with the WHO’s 5 micrograms. During the Trump administration, EPA staff recommended lowering the annual federal threshold to between 8 and 10 micrograms per cubic meter, but the Trump administration kept the standard set in 2012.
For decades, Black, Latino, Asian, Native Americans and low-income White residents have said deadly pollution in and around their homes has been their reality. They have questioned national air quality standards and data from fixed air quality monitors that said the concentration of pollution is acceptable.
“That’s not what the community is experiencing,” Veronica Eady, senior deputy executive officer for policy and equity at the Bay Area Air Quality Management District, said about the data. “We suspected some of these things but we didn’t have this," she said, referring to the community-scale granular data. “We’re taking this pivot to add additional tools to the toolbox to improve public health.”
During the many years before the pivot to monitoring pollution block-by-block near the source, there were “people dying that didn’t have to die,” said Margaret Gordon, a community activist and co-director of the West Oakland Environmental Indicators Project. Data provided by hyperlocal monitoring could have led to better planning and siting of pollution sources “where people work live and pray,” Gordon said.
In the area around the project’s office, bracketed by freeways and a major shipping port that serves as a destination for diesel trucks, the level of nitrogen dioxide pollution is 10.5 parts per billion, according to Aclima’s analysis. That lies well below the EPA standard but exceeds international guidelines.
The air quality is much better in one block of the mostly White Oakland Hills, which is far from freeways and the port. At 4.5 parts per billion, the nitrogen dioxide level lies below WHO’s standard, according to Aclima’s data, and the neighborhood’s PM2.5 concentration is at the global threshold.
Aclima ended its first phase of air quality mapping in 2021, when its researchers started to analyze the data. In addition to capturing the heavier pollution burden borne by Latino, Asian American and Black residents, it showed higher exposure for White and non-White residents who either rent their homes, live at two times below the federal poverty line or both.
These patterns are clear in Santa Clara County, home to racially diverse San Jose and Gilroy, a majority White exurb 33 miles south.
Both areas have elevated levels of particulate matter. In Gilroy, major highways slice through fields and farmland dotted by homes, and in San Jose, highways cut through minority and disadvantaged communities.
Dust also hangs in the air over Gilroy, kicked up by farming practices, and San Jose’s traffic pollution is exacerbated by a natural air basin that traps particulate matter from fires during wildfire season.
About an hour north in Alameda County, which includes Oakland, around 70 percent of the 180,000 Black residents “live in areas with nitrogen dioxide higher than the latest World Health Organization guideline,” the analysis said. That compares to about 40 percent of its White residents.
A growing body of scientific evidence suggests a link between breathing pollution, developing a severe illness and becoming infected or dying from covid-19. A study of 425 young adults, published last month in Sweden, found that brief exposures were “associated with increased risk of SARS-CoV-2 infection despite relatively low levels of air pollution exposure.”
Sacoby Wilson, a professor of environmental health at the University of Maryland’s School of Public Health who serves on Aclima’s environmental justice advisory board, called stationary air quality monitoring “a problem.”
“It’s really a poor approach,” he said. “We call it ‘exposure misclassification.’ ” When you compare the levels of pollution Aclima found to WHO guidelines, Wilson said, “It’s like, ‘Oh my God.’ It’s not just a race issue. You have to look at both race and income.”
The company’s hyperlocal monitoring is well ahead of the EPA, he added. “What they’re doing is new because it’s mobile based.”
The EPA, he said, is “30 to 40 years behind where they need to be.”
Bay Area officials defended the monitors they have in place, saying they accurately reflect the region’s pollution. Aclima’s scientists agreed, saying that when their mobile monitors drove near stationary monitors they collected similar data.
But as their cars drove farther away into communities, the discrepancies were undeniable.
Aclima has deployed its fleet of more than 150 air monitoring vehicles in other regions in the state, such as greater Los Angeles and San Diego. In the near future, company officials said, it will share results from large-scale hyperlocal pollution studies in the Midwest, the Mid-Atlantic between Virginia and New York, and in the South.
State and local government agencies, utilities, community groups and private companies like Google are interested in its data collection, said Davida Herzl, Aclima’s co-founder and chief executive, whose firm started operations in 2010.
The Bay Area Air Quality Management District turned to Aclima when a 2017 state law gave local agencies hundreds of millions of dollars to identify areas overburdened with pollution.
Nitrogen dioxide is mostly generated by heavy traffic such as cars, industrial trucks and other pollution sources. They are a constant presence on Interstate 880, which cuts through West Oakland’s high concentration of Black neighborhoods.
Under the rules of the California Department of Transportation, known as CalTrans, White people in Oakland are essentially guaranteed to breathe cleaner air. Heavy trucks have never been allowed on Interstate 580, which snakes around a higher concentration of White communities.
Racial disparities were also evident in San Francisco, where pollution in both the freeway-adjacent Tenderloin and Mission districts is significantly higher compared with areas such as the mostly White and higher-income Castro and Noe Valley, which sit far from major roads.
The history of the Tenderloin and Mission are a major part of that story, said Melissa Lunden, Aclima’s chief scientist. They were identified as undesirable areas by the federal Home Owners Loan Corporation in the 1940s for having too many Mexican, Asian and Russian immigrants, as well as Black people.
After they were redlined as areas where lending should be avoided, freeways, heavy industry and higher pollution soon followed. “West Oakland didn’t have freeways before the redlining maps, but it does now,” Lunden said.
Environmental justice activists have suspected a tie between redlining and pollution for decades: Researchers from five universities confirmed those suspicions in a major study last year.
The analysis found that 45 million Americans who live in areas that were formerly redlined are breathing dirtier air. Compared with White people, Black and Latino Americans live with more smog and fine particulate matter from cars, trucks, buses, coal plants and other nearby industrial sources in areas that were redlined.
Like Margaret Gordon in Oakland, the researchers noted that stationary air quality monitors failed to record the extent of the pollution in those overburdened areas. That, Herzl said, is about to change because of technology like Aclima’s.
“This represents a breakthrough in how we can manage the health of our environment in a data-driven and human-centered way,” Herzl said, noting that the nation’s air enforcement system was established a half-century ago. “The world has changed a lot in that time.”
