The Washington state Department of Ecology has approved a change to the state's plan for reducing haze in wilderness areas and national parks — a change which zeroed in on further reducing emissions at TransAlta's Centralia power facility.

If the power plant emits pollutants that contribute to haze, TransAlta will be required to install controls to reduce emissions of nitrogen-oxide emissions from its coal-fired facility by 12.5 percent, according to Ecology.

TransAlta will then be required to study how best to optimize newly installed controls to reduce emissions, and the studies could help bring emissions levels even lower.

TransAlta hopes to have the new emission controls installed and operational by January 2013, said TransAlta spokesman Michael Wagar.

TransAlta achieved a 95 percent reduction in sulfur-dioxide emissions from installation of scrubbers in smokestacks at the facility in 2001, according to Wagar.

Nitrogen-oxide emissions were already reduced by 20 percent when the company switched to a cleaner-burning type of coal, both Wagar and the Department of Ecology said.

TransAlta is still on schedule to close one coal-fired boiler by 2020 and the second by 2025 as part of an agreement with the state of Washington signed earlier this year as part of Senate Bill 5769.

Company officials have said they may replace the coal facility with a natural-gas plant at some point, but they don't yet know the cost and whether there is market demand for the facility.