A good rule of thumb is to never believe anything you read in the Trib
Kennecott is not the reason we have severe pollution in the wintertime. According to the 2014 DAQ report, "Point Sources" -- which includes Kennecott -- only account for 13% of PM 2.5 pollution along the Wasatch Front.
In fact, Kennecott has significantly cut their emissions over the past 30 years, to the point where Salt Lake and Tooele counties are no longer in violation of federal SO2 standards.
This graph shows just how dramatic the reduction in pollution from Kennecott has been: