Environmentalists are asking D.C. Mayor Vince Gray to put an Alexandria-based power plant on the fast track to closure.

The group wants Gray to file a special petition with the Environmental Protection Agency to force the plant to clean up or shut down.

The Sierra Club met with residents in Southeast D.C. last week to warn about the dangers of the sulfur dioxide emitted by the Potomac River Generating Station in Alexandria.

"We quite frankly would like to see it shut down," Sierra representative Irv Sheffey said.

The Sierra Club did its own study that indicated that sulfur dioxide was being blown across the Potomac River from Alexandria to the city's Ward 8.

"We're concerned about people's health. This is a tangible indicator that there's something going on in the air we need to be concerned about," Sheffey said.

The EPA links sulfur dioxide with asthma and other respiratory diseases.

Arnitta Coley, a 65-year-old Ward 8 resident who attended the meeting, said she has problems breathing and knows many people with asthma.

"The air quality is very, very bad," she said. "I don't know how many more things we can take."

Gray last week voiced concerns about the sulfur dioxide. But the mayor's office said they were still evaluating how shutting down the plant would hurt the District's power supply, and said there are no immediate plan to petition the EPA.

Genon, which owns the Alexandria plant, said it complies with all state sulfur dioxide regulations. The plant reduced sulfur dioxide emissions by 80 percent since 2000 and would make additional investments in reducing pollution if necessary, the company said.

Power plants across the country face problems similar to those facing the Alexandria plant. Earlier this year the EPA issued new sulfur dioxide standards, due to go into effect in 2017, that plants may either have to spend hundreds of thousands of dollars to meet or shut down. The Sierra Club's effort is intended to force the Genon plant to make that decision much sooner.

Alexandria wants the power plant shut down. Genon promised the city in 2008 that it would add $34 million of pollution controls -- but those measures did not curb sulfur dioxide, officials said.