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January 18, 2009
During the past three winters, ozone—normally linked to hot-weather and urban pollution—has soared to health-threatening levels near a remote natural gas field in northwestern Wyoming. Now, scientists at NOAA’s Earth System Research Laboratory have solved the problem of how ozone can form in cold weather at levels threatening to human health.
Their results, published Jan. 18 in the journal Nature Geosciences, are forcing researchers to rethink the mechanics of ground-level ozone production.
The NOAA analysis, the first ever for rapid ozone production in cold temperatures, suggests the problem could be more widespread.
“Rapid production of wintertime ozone is probably occurring in other regions of the western United States, in Canada, and around the world,” said lead author Russell Schnell, with the NOAA research lab. “Wintertime ozone could be forming wherever gaseous fossil fuels are being extracted in conditions similar to those at the Wyoming site.”
Among other likely areas are Russia, Kazakhstan, Mongolia, and China, according to Schnell. Ozone measurements in most of these regions are limited or nonexistent in winter.
A main ingredient of urban smog, ozone can cause severe respiratory effects, especially in children, the elderly, and asthmatics. It also damages crops, trees and other vegetation. The Environmental Protection Agency sets air-quality standards for ground-level ozone pollution in the United States.
Ozone’s harmful contribution to smog is far different from the chemical’s effect high in the atmosphere, where the natural ozone layer blocks damaging solar radiation from reaching Earth’s surface.
The NOAA team found ozone was rapidly produced on frigid February days in 2008 when three factors converged: ozone-forming chemicals from the natural gas field, a strong temperature inversion that trapped the chemicals close to the ground, and extensive snow cover, which provided enough reflected sunlight to jump-start the needed chemical reactions.
Motor vehicle exhaust, industrial gases and other urban emissions, as well as natural sources, produce the chemicals that then form ozone. But it was previously thought direct sunlight and hot weather were also required for high ozone concentrations to occur. For that reason, ozone is routinely monitored only between April and October in the United States.
But from January to March 2008, instruments near the Jonah and Pinedale Anticline natural gas field showed that on 14 days ozone exceeded the Environmental Protection Agency’s standard of 75-parts-per-billion (ppb) averaged over eight hours. At times, single-hour averages topped 140 ppb—rivaling peak summertime levels of 150 ppb measured in highly polluted cities. The state of Wyoming issued its first ever wintertime ozone advisories during those months.
The Jonah and Pinedale Anticline site, located in Wyoming’s Upper Green River Basin, is one of the largest and most concentrated natural gas fields in the United States. In 2007 energy companies extracted more than $4 billion of natural gas—enough to provide the natural gas needs of 17 million U.S. homes for a year.NOAA understands and predicts changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and conserves and manages our coastal and marine resources.