GRANTS PASS, Ore. -- A new report indicates that Oregon's only coal-fired power plant is responsible for half the particulate pollution in the Columbia River Gorge when air quality conditions are at their worst.

The report found that the 28-year-old Portland General Electric plant at Boardman typically contributes an average of 14.9 percent of the fine particles gathered at a federal air quality monitoring site in the gorge.

But that spikes to 55 percent in November, when east winds push the air downstream along the Columbia River.

The analysis of 12 years of federal air quality data was done by University of Washington Professor Dan Jaffe for the Yakama Indian Nation.

It was released by conservation groups that plan to sue PGE to force the utility to take greater steps to clean up haze-producing emissions from the plant.

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PGE spokesman Steve Corson said the utility has not had a chance to analyze the report, but it's going forward with plans to reduce emissions.