Poor Nipomo Mesa air linked to off-roaders 

• PHOTO BY STEVE E. MILLER
• UP IN THE AIR: Off-road vehicles at Oceano are polluting the air around Nipomo Mesa with sand and dust particles. But what can be done?

High levels of coarse airborne particles—small enough to breathe in—are the root cause of the problem, and not necessarily vehicle exhaust emissions or operations at ConocoPhillips.

According to the study, off-highway vehicles (OHVs) break up the natural crust that forms on the surface of the Oceano sand dunes. The breakage, coupled with a lack of plants growing where OHVs travel, primes particulates to float from the dunes to the populated mesa.

The study reported that particles far exceed the current state health standard for PM10 (airborne particles with a mean aerodynamic diameter of 10 microns or less) in many places on the mesa.

Population-based studies in hundreds of U.S. cities have shown that both long- and short-term exposure to such high particle levels can cause significant spikes in hospital admissions, emergency room visits, asthma attacks, and even premature deaths.

Phase One of the study began in 2004 and concluded air quality on the Nipomo Mesa exceeded the state standard, but failed to prove vehicular activity in the dunes played a role. The field measurement portion of Phase Two ran between January 2008 and March 2009, producing data that required nearly a year to review.

Among the findings of Phase Two: The offending particles don’t come from an offshore source, and neither petroleum coke piles at the ConocoPhillips facility nor agriculture activities in the area are a significant source of particulate matter on the mesa.

The particles, the study found, are mostly sand blown to the mesa by strong winds. The open sand sheets where OHVs ride emit significantly greater airborne particulates than undisturbed areas under the same conditions.

The report doesn’t make any recommendations on how to curb the particles’ effects on air quality, and it stops short of suggesting any restrictions to recreational off-roading.

The study is available for public review at the South County, San Luis Obispo, and Paso Robles public libraries, or online at the Air Pollution Control District’s website: slocleanair.org.

The District has scheduled a public workshop from 6 to 9 p.m. on March 3, at the South County Regional Center, 800 W. Branch St. in Arroyo Grande, to discuss the study results. A panel of experts will explain study design and sampling methods, as well as take questions from the public