Will Oceano Dunes vehicle closure prove what’s causing dust pollution?
With the Oceano Dunes State Vehicular Recreation Area closed for COVID-19 precautions, off-road vehicle riders see an opportunity for final proof of how much dust in downwind communities is caused by vehicle activity and how much is natural.
An April 6, two-page letter from the Scientific Advisory Group researching the issue indicates it’s not going to be that simple.
In short, the scientists say that while the dunes are naturally dusty, vehicle activity has had a long-term effect that won’t go away overnight. Restoring the landscape to pre-vehicle conditions could take years.
In the letter, the group suggests decades of riding may have exposed sand surfaces that emit more dust, or perhaps “the availability of of dust-sized grains for emissions is greater today than decades ago.”
The San Luis Obispo County Air Pollution Control District distributed the letter on its website and in an emailed press release, saying it was in response to questions as to whether the abrupt closure will show particulate matter (PM) emissions eliminated or substantially reduced to “natural” levels during this closure period.
The statements in the letter are similar to what the group has said before, but with more detail.
Last year, the Scientific Advisory Group said the dust plume isn’t necessarily caused by vehicles kicking up dust that drifts downwind and it’s not vehicle emissions. Rather, “the sand is more emissive than it would be in the absence of OHV activities.”
Here’s what the Scientific Advisory Group said in its recent letter:
“The (Scientific Advisory Group) acknowledges that the Oceano Dunes are a naturally dusty surface that would experience PM emissions even in the absence of human activity, especially during this spring windy season,” the letter says.
“But the SAG is also clearly aware that decades of OHV activity have fundamentally altered the natural beach-dune landscape, making the dunes significantly more susceptible to PM emissions than they would be in a natural state.
“The SAG does not expect a few weeks or months of temporary OHV restrictions to substantially alter the balance of human versus natural contributions to PM emissions at ODSVRA.”
High dust levels still being measured
In the last few weeks, air pollution on the Nipomo Mesa has reached high levels a few times even without vehicles on the beach, according to monitors operated by the San Luis Obispo County Air Pollution Control District. Still, long-term heavy vehicle use could contribute to unhealthy levels of particulate matter.
The SAG letter points to some examples of evidence that vehicle activity increases dust emissions, including:
- Multiple measurement projects revealed that areas of the dunes with the most intensive OHV activity tend to produce the highest dust emissions.
- Undisturbed areas like Oso Flaco tend to emit less PM dust.
- The most noticeable reduction in PM measurements was a result of closing parts of the park to OHVs and installing wind fences, straw bales, vegetation plantings and other measures to reduce wind erosion.
How long restoration takes is unknown.
“The time required for the dust emissions from the dune sand to reach levels similar to those prior to large-scale OHV activity remains unknown. The dunes, sediments, and vegetation will each require time to reestablish to a new lower regime of disturbance,” the letter says.
“This could be on the order of years to decades, left to nature’s devices,” and “a few weeks or months of temporary OHV restrictions may not be sufficient to result in substantial declines in PM emissions.”
Nimomo Mesa has history of unhealthy air
For years, air quality monitors on the Nipomo Mesa have shown unhealthy levels of particulate matter on days when strong winds blow from the direction of the Oceano Dunes.
On May 4, 2018, the Department of Parks and Recreation and the Air Pollution Control District agreed on a goal to reduce emissions from the park by at least 50% in four years.
The Department of Parks and Recreation has been studying aspects of this issue for years with the assistance of the Desert Research Institute and, more recently, with Scripps Institution of Oceanography at UC San Diego.
In these endeavors, “it is important to note,” the Scientific Advisory Group says, “that such restoration measures will never achieve complete elimination of natural PM emissions at ODSVRA.”
Instead, the letter says, “the goal is to achieve significant and sustained PM emissions reductions toward attainment of state and federal air quality standards.”
“Only through sustained restoration projects does the SAG expect to see a significant reduction in PM emissions.”
The letter is signed by Scientific Advisory Group Chair Dr. William Nickling, along with Dr. Raleigh Martin; Dr. Ian Walker; Dr. Jack Gillies; Carla Scheidlinger; Earl Withycombe and Mike Bush.
To read the complete letter, visit: www.slocleanair.org/air-quality/oceano-dunes-efforts.php
This story was originally published April 14, 2020 at 2:43 PM.
