Background Ozone is a Major Issue on US West Coast

Levels of "background ozone" -- ozone pollution present in a region but not originating from local, human-produced sources -- are high enough in Northern California and Nevada that they leave little room for local ozone production under proposed stricter U.S. ground-level ozone standards, finds a new NASA-led study.
The researchers, led by Min Huang of George Mason University, Fairfax, Virginia, used a novel technique that combined data acquired from two instruments on NASA's Aura spacecraft in the summer of 2008. The technique more accurately determines levels of background ozone and their relative contribution to total surface ozone levels. Integrating Aura satellite data into the study increased the estimates of background ozone by an average of 2.4 parts per billion (ppb) over previous estimates, an amount that varied by 4 to 11 ppb over the two states. Huang conducted the study while a postdoctoral scholar at NASA's Jet Propulsion Laboratory, Pasadena, California.
The new method of integrating satellite data may help provide states with a scientific basis to request exemptions to the federal air quality standards for ground-level ozone proposed by the U.S. Environmental Protection Agency. EPA proposed lowering the standard from the current 75 ppb set in 2008 to between 65 and 70 ppb, following a review of public data on the negative health effects of ozone pollution. EPA is required to announce a final decision by Oct. 1.

Background ozone can be produced from natural local sources such as wildfires, and transported via winds from distant sources, such as the stratosphere or another region or country.
The NASA study found that, on average, background ozone sources generated about 48.3 ppb, or 77 percent, of the total ozone in the study region of California and Nevada. The findings are particularly important in Northern California and Nevada, where wildfires and ozone transported to the region from abroad can cause background ozone to exceed 60 ppb. The lowest background ozone levels were seen in Southern California, where topography helps trap local emissions.
"Our study shows background ozone plays a significant role in Western U.S. ozone levels under high-ozone conditions, and varies considerably by region, with higher values in many rural regions," said Kevin Bowman, study co-author and principal investigator of Aura's Tropospheric Emission Spectrometer (TES) instrument at JPL. "Some regions in the West have high background ozone levels that leave less than 10 parts per billion for local ozone production under the EPA's most aggressive proposed ground-level ozone standards."