Is Pollution From Asia Making the Central Valley's Bad Air Even Worse?

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(David McNew/Getty Images)
Advocates say the San Joaquin Valley Air District should focus on sources it can control, like farming machinery. (David McNew/Getty Images)

By Alice Daniel

California’s Central Valley grapples with some of the dirtiest air in the nation. The culprits range from its vast agriculture industry to trucks on Highway 99. But one local air district is tagging a source far away: Asia.

“The world in so many ways is getting smaller in respect to what we always thought was our own backyard issue: ozone,” says David Lighthall, the health science advisor for the San Joaquin Valley Air Pollution Control District.

Lighthall is one of the organizers of an ozone pollution conference starting Tuesday where scientists from California, China, Colorado and other places will discuss trends in global ozone.

Scientists say pollutants from fast-growing Asian countries like China are blowing across the Pacific Ocean and increasing ozone levels in vulnerable areas that include parts of California. But how much of a difference that foreign -- or "transboundary" -- ozone makes in the Central Valley is debatable.


Lighthall says that on some days this additional pollution is enough to prevent the district from meeting federal clean air health standards. The Valley's bowl-shaped geography traps pollutants, sometimes for days at a time -- and that includes pollutants from other places, Lighthall says.

He says there's an "upward trend" in transboundary ozone and the ozone is now "mixing down and really making a difference on certain days as to whether we actually meet the standard ... or whether we don’t meet it,” Lighthall says.

But the EPA disagrees. It says that on the Valley’s worst air days, most ozone pollution comes from local sources. In fact, last year the air district unsuccessfully petitioned the EPA to exempt it from penalties for violating a health standard blaming it on smog from Asia.

Some local health advocates say the air district is straying too far from home.

“The air district is famous for looking for loopholes,” says Delores Weller, director of the Central Valley Air Quality Coalition, an advocacy group.

She says the district is focusing on sources it can’t control and should do everything it can first to tackle homegrown pollution.

“It would be great to see an agriculture, farming operations and air pollution conference based here in the Valley as opposed to a trans-boundary ozone conference,” Weller says.

But the air district says it must research all sources of air pollution to know exactly what it’s dealing with and how best to mitigate. It’s even funding research at U.C. Davis to assess the effects of ozone from Asia.