Please note this was not your regular Clean Air regs that were being enforced. This strictly has to do with "visibility". As the this site explains:
The Clean Air Act requires BART (Best Available Retrofit Technology) review when any source that “emits any air pollutant which may reasonably be anticipated to cause or contribute to any impairment of visibility” in any 156 Federal Class I area. The Regional Haze Rule (RHR) and Section 169A of the Clean Air Act have as their goal the restoration of visibility in mandatory Federal Class I areas, including national parks and monuments, to pristine conditions by 2064.
Federal Class 1 areas are National Parks, National Monuments and Wilderness Areas. All such areas in existence as of August, 1977 are now in "Mandatory Class 1 Areas" including those in NM (see this map). New Class I areas can be added by the state at any time.
Once the enviros get the number of Monuments and Wilderness areas they want, I expect them to start petitioning the state to designate additional Class I areas in NM.
Think of our clean air problems here in Dona Ana County, with all the pollution floating in from Juarez and El Paso. We have a huge new National Monument. Now think of what stringent requirements would be imposed to reach "pristine conditions" of visibility. The National Monument designation wasn't just about land. It was about land and air and development in general.