CENTRALIA, Wash. - It's another round in the fight for cleaner air in Washington. Conservation groups have appealed an air pollution permit issued to the only coal-fired power plant in the state, located in Centralia. They say the plant, owned by Canadian company TransAlta, produces about 10 percent of the global warming pollution in the state.

Attorney Joshua Osborn-Klein with Earthjustice, the law firm that filed the appeal on behalf of the groups, says the state has been in negotiations with TransAlta for years - but has not taken a tough enough stance on reducing the plant's emissions.

"Those mercury controls that have been proposed would be voluntary reductions; and the nitrogen oxide haze pollution controls would not require the type of technology that is recognized as being available and effective at reducing that kind of pollution."

The appeal asks for new controls on carbon dioxide and mercury emissions at the plant, as well as stronger controls for the haze it produces. TransAlta says the company is looking into new pollution control technology, but calls it a distant and expensive option.

In June, some of the same groups that filed the appeal - including the Sierra Club and the National Parks Conservation Association - asked the U.S. government to get involved, too. They said the haze from the plant hampers visibility and affects air quality in several national parks.

Osborn-Klein says the plant has to get a permit every five years; he thinks the time is right for stricter controls.

"Washington is taking important steps toward protecting public health, but it's just missed the ball on this one. TransAlta is a big facility. It's the number one source of mercury emissions in the state, a major source of nitrogen oxide emissions in the state, and the number one single source of global warming pollution in the state."

The Southwest Washington Clean Air Agency issued the permit, which must be reviewed by the Washington State Pollution Control Hearings Board. The appeal was filed with the board. The U.S. Environmental Protection Agency will also review the permit.