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  The Environmental Protection Agency has issued its final rule aimed at cleaning up the largest single source of haze-causing pollutants in the country.  

  Rather than mandate that the Four Corners Power Plant take one avenue to reduce nitrogen oxide emissions, the EPA is giving the plant's operator a choice.

  Arizona Public Service can either upgrade the five units at the northwestern New Mexico plant or go with its own plan to shut down three units and install pollution controls at the two others.

  The actions would cut emissions by 80 percent and 87 percent, respectively. The pollutants cloud the air at places like the Grand Canyon.

  APS must notify the EPA of its decision by July 1. It then would have around five years to implement the rule.