Some Bay Area neighborhoods breathe more hazardous air. Here’s where they are.

Over the years, growing evidence has revealed a stark injustice: residents of the Bay Area’s poorer cities are far more likely to be exposed to smog and soot than those in rich ones.

Now, a data-driven map of individual neighborhoods in the San Francisco Bay Area and California’s three other major metro regions shows, in great detail, just how precisely those disparities hold true.

“The poorest people have the highest exposure,” said researcher Jason Su of UC Berkeley’s School of Public Health, whose team’s work is published in this week’s issue of the journal Science Advances.

The new study gives a more fine-grained snapshot than previous research of the different experiences of varied communities, from the traffic-ridden transit corridors of the East Bay to quiet and affluent suburbs in Peninsula hills. It can help inform disease surveillance and provide state officials with the data needed to target interventions.

“Research like this highlights the fact that clean air is an equity imperative. That’s why the California Air Resources Board is prioritizing equity and justice in climate and clean air investments, to ensure no one is left behind as we work toward a clean air future in California,” said board spokesperson Amy MacPherson.

The study found, for instance, that nitrogen dioxide, or smog, is more prevalent in low-income pockets of East and West Oakland, which are boxed in by Interstates 80, 880, 580 and State Route 24. It’s also higher in the working class communities of Richmond, San Leandro and East San Jose, which also are traversed by major traffic routes.

By contrast, the air is far cleaner in greener, more windswept and prosperous neighborhoods, such as Alameda, Redwood Shores, Millbrae and the Berkeley Hills.   .

Exposure to fine particulate matter, or soot, follows a similar pattern. Levels are elevated in East San Rafael, at the base of 580’s Richmond San Rafael Bridge, for example. Soot is also more common in Redwood City, between the busy Highway 82 and 101 corridors, and Martinez, where Interstate 680 crosses the Benicia Bridge.  There is less soot in neighborhoods in Corte Madera, Burlingame, Foster City and the hills above Milpitas.

Some of the most polluted communities are victims of geography: They sit in basins, where dirty air collects. A few live alongside power plants, hazardous waste generators or other types of polluting infrastructure.

But the vast majority are affected by the Bay Area’s nonstop traffic. Throngs of passenger cars, SUVs and trucks emit nitrogen dioxide, which can cause asthma and other respiratory problems. Vehicle engines also discharge soot, which is linked to lung cancer and cardiopulmonary disease.

“Traffic is the primary source of air pollution,” said Su, whose team included experts with UCSF’s School of Medicine, UCLA’s Fielding School of Public Health, the San Diego device company ResMed Inc. and San Francisco’s Propeller Health, whose sensors and software do data analysis.

Previous research has blamed pollution in lower income neighborhoods to redlining, a practice beginning in the 1930s that denied home loans to those of some races of ethnicities in certain affluent communities. While this discriminatory practice officially ended in 1968, it influenced present-day zoning practices and the placement of highways and industries.

Air quality in California has been greatly improving since the 1970s-era passage of the Clean Air Act, its 1990 amendments and even stricter state-specific measures.

But progress has happened faster in some communities than in others. The gap is closing, said Su, but still starkly evident.

The research was conducted using cutting-edge machine learning and massive data processing to produce high-resolution daily air pollution maps for smog, soot and ozone across California between 2012 and 2019.

The maps were created using terabytes of data from 850 monitoring stations and multiple other data sources, including traffic, weather, land use and different geographic features around the state.

The datasets generated detailed pictures of air pollution in four metro areas — San Francisco Bay Area, Los Angeles, Fresno and Sacramento — at the census tract level, based on race, ethnicity and socioeconomic disadvantage.

Most previous research studied only large geographic regions at a low resolution of 3 to 10 miles. It was conducted within broad timeframes, perhaps only once a year. And monitoring sites were sparsely distributed. Su said exposure differences between advantaged and disadvantaged communities couldn’t be distinguished.

This new study compares exposures within geographic areas as small as one-tenth of a mile. It focuses on concentrations of two specific pollutants — smog and soot — because they are most closely linked to health problems. It found that disadvantaged communities had higher concentrations than advantaged communities.

But there was good news: During the course of the seven year study, exposure decreased. And the most disadvantaged communities saw the largest reductions in exposure.

The team also measured ozone, a secondary pollutant not directly emitted by traffic or industry but created by the sun’s heating of pollutants. In general, affluent or rural neighborhoods in California are experiencing rising concentrations of ozone due to what’s called “the ozone paradox.”  Ozone, which can irritate the airways, is degraded by smog, which is more common in cities.

The Bay Area had relatively low concentrations of ozone, according to the research.

Recent efforts to reduce emissions from transportation, such as plug-in electric vehicle tax credits and stricter exhaust emission standards for heavy-duty engines, are a step in the right direction, Su said.

But he worries that some non-engine pollutants will persist, such as particulate matter from tires, brakes and the road’s surface itself.

Statewide, disadvantaged neighborhoods in the Los Angeles metro area had the highest concentrations of smog and soot.

In the Los Angeles area, 79% of disadvantaged communities experienced high concentrations of smog, compared to 6.2% in the Bay Area, 4.0% in Sacramento and 0.1% in Fresno. Los Angeles also highest concentration of soot, experienced by 70.4% of disadvantaged communities, compared to 67% in Fresno, 62% in Sacramento and 6.2% in the Bay Area.

“The Bay Area is the best — the lucky one,” Su said.