This isn't just about the NPS and NPCA not wanting to be impacted by coal burning power plants -- it's the law. The 1977 Clean Air Act requires that all national parks larger than 6000 acres that existed when the law was passed have the highest degree of protection from air pollution impacts of any lands in the US. It's called "Prevention of Significant Deterioration" and the Federal Land Manager (the Secretary of the Interior, and through him/her, the Director of the NPS) has an "affirmative responsibility" to protect the air quality related values of these parks. Unfortunately, it's always been a political football and a hollow protection since regulation and enforcement depends upon EPA and the states to act.

J Longstreet
a national park superintendent