This article originally appeared in the San Francisco Chronicle’s health section on December 5, 2012 under the headline “Bay Area breathes easier, ozone data shows.”
Compared with Southern California, living in the Bay Area is a breath of fresh air. That’s according to air pollution data from the Centers for Disease Control and Prevention. Based on the number of days per year in which smog, soot and other ozone emissions surpass U.S. regulatory standards, the Bay Area’s nine counties fall well below the state average. This is good news, as breathing pollution puts people at risk for asthma and other medical conditions.
Los Angeles and surrounding counties in Southern California top the list of high-pollution days, in part because they have more people and more cars. But according to a Stanford environmental expert, geography may be as much to blame for the poor air quality as the people who live there.
Here are the numbers:
The average number of days in which California counties had ozone concentration levels above U.S. regulatory standards in 2010, the most recent year data is available.
The number of days San Francisco, Marin and Solano counties were above ozone standards in 2010. Santa Clara, San Mateo, Contra Costa, Alameda and Napa counties each had less than a week of above-standard days. Sonoma County had 11 days.
The number of days San Bernardino County spent above ozone concentration standards in 2010 – the highest in the state. Four of the top five counties were in Southern California.
The percentage of California’s population that lives in those four Southern California counties: Los Angeles, San Bernardino, Kern and Riverside. But according to Mark Z. Jacobson, professor of civil and environmental engineering at Stanford, SoCal’s geography plays a bigger role in air quality than do its many cars and industries. These counties are prone to high barometric pressure that traps the pollution close to the ground.
The Bay Area has its fair share of emissions, Jacobson said, but lower barometric pressure means that the pollutants can rise three times as high – up to 3 kilometers above the Earth – where people don’t breathe them in.