A Tucson power plant will replace two coal-fired generators with ten natural-gas engines.

The old engines at the H. Wilson Sundt Generating Station were installed in the 1950s, and the Pima Department of Environmental Quality said the move to natural gas will lead to less emissions overall.

However, the change will mean more nitrogen oxide pollution which leads to higher ozone levels.

Pima DEQ says the increases won’t violate the Clean Air Act, but Sandy Bahr, director of  the Sierra Club’s Grand Canyon Chapter, says any pollution increase is unacceptable.

“This plant is in a neighborhood that is predominately low income and people of color and there are significant environmental justice issues with this facility,” she said.

Tucson Electric Power, who runs the generating station, said they have recently made investments in renewable energy, but this change is needed to ensure consistent coverage.