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By MIKE LEE 

In the daylight, the storage tank looks innocuous. It’s the same sort of tank that can be found next to any oil or gas well in the West, and there are hundreds like it in Fort Worth.

But in infrared light, a plume of vapor can be seen escaping from the tank’s vent.

The video, taken by the Environmental Protection Agency at a site in Colorado, is a vivid illustration of a problem that’s beginning to draw attention: the amount of air pollution produced by natural gas extraction in the Barnett Shale field.

Researchers are only beginning to wrap their hands around the issue, but the early findings indicate that natural gas production is a significant part of North Texas’ air pollution problem. And it could be growing. At the least, it’s worth studying to determine the scope of the problem, the researchers said.

There has been extensive research on emissions from cars and trucks, which account for much of the air pollution in North Texas. There’s also been research into pollution from electric and cement plants.

"All those other sources have seen a lot of regulation," said Al Armendariz, an engineering professor at 91��Ƭ�S�ϼ� who has studied air quality issues for several years. "The oil and gas sector kind of snuck by." . . .

Another source of pollution is the compressors used to move natural gas through pipelines. The compressors are usually powered by large engines — often running on natural gas from the same pipeline — and some of them have no emission controls.

Armendariz said he’s still finalizing the study, but he estimates that the compressors in the Barnett Shale field have a combined 2 million horsepower. That’s the equivalent of about 10,000 full-size pickup engines — in a region with 4.5 million people.

But unlike cars and trucks, "these engines are out there running 24-7," Armendariz said. "The newer ones are pretty clean, but they’re still not as clean as the newest automobiles."

The environmental quality commission began phasing in pollution control rules for compressor engines last year. Commission officials said in a statement that those controls "will have benefit toward reducing" the ozone problem by 2009.

But Armendariz said the commission is focusing only on some of the counties and on some of the engines that are producing oil and gas. And, he said, the state may have underestimated the number of compressors in the Barnett Shale. He is preparing a study that calculates the amount of pollution from compressors and other sources.

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