The Mohave Power Project (MPP) is a large (1590 MW) coalfired power plant located 90 miles southeast of Las Vegas in Laughlin, Nevada. Constructed in 1971, the plant was, for some time, the largest emitter of sulfur dioxide in the western United States. In 1998, a group of environmental advocacy organizations sued the plant’s owners, alleging that its emissions of sulfur dioxide and particulate matter were in violation of the Clean Air Act. Approximately one year later, the plant was identified as a major cause of visibility impairment in Grand Canyon National Park (GCNP) by the U.S. Environmental Protection Agency (EPA). Upon completion of a multi-year study referred to as Project MOHAVE (Pitchford et al., 1999), the EPA concluded that, although other sources contribute to the visibility reduction, “[because] of the quantity of SO2 emitted from the Mohave Generating Station and its proximity to the Grand Canyon, no other single emissions source is likely to have as great an impact on visibility in the Park”.

A few months after this determination, the plant’s owners settled the lawsuit and entered into a consent decree which required the plant to reduce SO2 emissions no later than 2005 (Consent Decree, 1999). Subsequently, the owners estimated that additional emissions controls would cost more than $1 billion and elected to close the plant on December 31, 2005 rather than make such an investment. Over four years have passed since the closure, and we now have the opportunity to determine whether, in the prolonged absence of plant operations, air quality in the Grand Canyon has improved.

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Effect of Coal-Fired Power Generation on Visibility in a Nearby National Park