Salt River Project has finished installing new clean air technology at its coal-fired power plant in St. Johns, Ariz.  The $470 million project meets EPA requirements to reduce haze over national parks in the Southwest.

SRP entered an agreement with the EPA to install the equipment in smoke stacks at the Coronado power plant in 2007. Construction was finished last week to reduce nitrogen oxide and sulfur emissions by nearly 90 percent.

SRP spokesman Scott Harelson said the goal is to limit the smoky haze over Grand Canyon and other parks.

"What impact that will have directly on the parks is relatively unclear because there are a number of different sources of haze at these parks,” Harelson said.

He said automobile exhaust and smoke from prescribed burns contribute to smoggy conditions at the parks. He said SRP has also started installing updated clean air equipment at its Navajo coal plant near Page, but the utility and the state of Arizona are challenging some federal requirements for that project.