Air pollution has improved in the San Francisco Bay Area since 2012

Air quality in the San Francisco Bay Area, as measured by fine particle pollution, has slightly improved since 2012.

Why it matters: Fine particles, generated from fossil fuel burning and other sources, can enter our bodies when we breathe, making their way to the lungs or bloodstream and causing myriad health problems.

Details: They are linked to nearly 11,000 excess deaths across the U.S. annually, by one estimate.

• Non-white and low-income Americans are at a higher risk of death from exposure to fine particle pollution compared to other groups, per a 2022 study published in Nature.
• Fine particles — also known as PM2.5 due to their tiny size of 2.5 micrometers — are the most hazardous form of particulate matter.

By the numbers: The three-year rolling annual average concentration of fine particle pollution across the Bay Area was 8.4 micrograms per cubic meter as of 2021 (the latest year for which data is available), compared to 8.5 in 2012 — a 1% decrease.

• Concentrations below 12 micrograms per cubic meter are considered healthy, the EPA says — though it is seeking to tighten that standard.

The big picture: Air quality generally improved nationwide during the height of the COVID-19 pandemic, in part because fewer people were driving.

• But as the pandemic ebbs and people's behaviors and activities return to normal, air quality nationally is worsening accordingly.

Yes, but: Air quality decreased notably between 2015 and 2021 in California, as well as other parts of Western states, where extended periods of extreme drought have created prime conditions for wildfires, and thus increased pollution from smoke:

Flashback: Remember "orange day," when it looked like we were living in an apocalyptic hellscape? Turns out, we kind of were.

• On that day in September 2020, air quality in most parts of the Bay was either good or moderate. But just two days later, San Francisco had a "very unhealthy" air quality index reading of 238 after the smoke from "orange day" settled to the ground, SF GATE reported.

What's next: The EPA in January proposed reducing its fine particle pollution standard from 12 micrograms per cubic meter to "a level between 9 and 10."

• The EPA is also taking other steps to improve air quality, including via newly proposed vehicle emissions standards.

Of note: Public health advocacy groups say the fine particulate standard should be even lower than the EPA's proposed range.

• The agency's proposal "misses the mark and is inadequate to protect public health from this deadly pollutant," the American Lung Association said in a statement.

The other side: Industry groups, meanwhile, argue that lowering the standard would be overly burdensome.

The bottom line: As the fight over lowering the fine particle standard heats up, the EPA once again finds itself at the heart of the climate change and public health debate.