Ozone Levels: Now a Wintertime Concern

Jan. 20, 2009 -- Researchers have detected a dangerous product of urban air pollution, surface-level ozone, lingering in the strangest of places: a rural Wyoming basin.

Commonly associated with sunny summer afternoons and city sprawl, ozone is toxic when inhaled, and it claims tens of thousands of lives globally each year. The threat to public health is well-known, and the U.S. Environmental Protection Agency already monitors the gas closely around the country.

And yet, it wasn't until last February that scientists first noticed that the poison was concentrating in the Upper Green River Basin in Wyoming, at levels almost twice what the EPA considers safe.

In a paper published Sunday in the journal Nature Geoscience, researchers suggest the basin regularly clogs with ozone each winter, and that ozone hazards may be going unnoticed in cold areas around the world.

"Ozone in winter has never been observed like this before," Russell Schnell of the National Oceanic and Atmospheric Association said. "We realized something really quite strange is going on here."

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Schnell and a team of researchers believe the ozone spike occurred when a high-pressure system moved into the area bringing calm, stagnant air with it. Without winds to mix the atmosphere, the cold, snow-covered ground kept air in the first two meters of atmosphere chilly, while upper air got warm.

"It forms an invisible glass ceiling that holds all this pollution in," Schnell said. "As soon as the sun comes up, boom, it ignites the chemistry."

Ozone needs a mixture of sunlight and pollutants to form. In the Upper Green River Basin, a sunny day plus a cover of fresh snow reflecting the sun's rays back through the atmosphere makes a perfect recipe for ozone.

The pollutants come from the basin's booming natural gas mining industry. Home to the 400 square-kilometer Jonah-Pinedale Anticline natural gas field, the area is teeming with vehicles, chemicals, and a transient labor force. Last year, the field produced about 20 million cubic meters of gas, worth $4 billion.

Strange pollutants cropping up near natural gas fields are probably par for the course. But Schnell points out that EPA ozone monitoring is only required in warm months. He thinks major cities that get lots of snow and have plenty of pollutants to go around, like Salt Lake City, Utah and Denver, Colorado, might have significant ozone hazards that are going undetected.

"You'd be hard-pressed to find someone who would've predicted the high levels the researchers see here," David Parrish of NOAA, who wasn't involved in the study, said. "But I'm reluctant to extend it to cities. There is monitoring in Denver, and we don't see high ozone there."

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