Large wildfires like those that raged through Southern California last fall come with a hidden danger: spikes in ground-level ozone, a lung irritant, that can occur far from the fire itself.
Even where little or no smoke is visible, ozone levels can rise above federal health limits, according to a new study by the National Center for Atmospheric Research in Boulder, Colorado.
"In Orange County, you can have a fire all on the eastern edge of San Bernardino County, but you might get the maximum ozone impact," said Gabriele Pfister, an atmospheric scientist and the study's lead author. "You might not see smoke anymore, or the smoke might be diluted by the time it reaches you, but the ozone might be highest in your county."
Pfister and her co-authors examined ozone measurements from 55 monitoring stations throughout the state when large wildfires broke out in September and October 2007. They also ran the data through computer models to determine how much of the ozone in the air was due to the fires, and how much was already in the atmosphere.
They found that ozone levels were three times more likely to rise above federal health limits when plumes from the fires were blown into an area. The broad area where ozone increased included rural California and even parts of Nevada.
The fires themselves don't release ozone gas; instead, just as with car exhaust, they release ozone "precursors" such as nitrogen oxides and volatile organic compounds.
When cooked by sunlight, these precursors can be transformed into ozone.
Ozone has a kind of Jekyll and Hyde relationship with the human species. In the upper atmosphere it protects against harmful ultraviolet rays, but near the surface it can aggravate athsma and other lung conditions.
Pfister said if wildfires are burning in the region, it is best to check for warnings or ozone pollution forecasts and adjust your plans accordingly.
If ozone levels are high, "try and limit your activities," she said. "Ozone concentrations are generally highest in the afternoon - noon to early evening. If you do any sports, try to do it very early in the morning, when ozone levels are lowest."
The study was published Thursday in the journal, Geophysical Research Letters.
Contact the writer: 714-796-7865 or firstname.lastname@example.org.