Comment on “Effect of coal-fired power generation on visibility in a nearby National Park (Terhorst and Berkman, 2010)”

Few electricity generating stations received more environmental scrutiny during the last quarter of the twentieth century than did the Mohave Power Project (MPP), a coal-fired facility near Grand Canyon National Park. Terhorst and Berkman (2010) examine regional aerosol monitoring data collected before and after the plant’s 2006 retirement for retrospective evidence of MPP’s impact on visibility in the Park. The authors’ technical analysis is thoughtfully conceived and executed, but is misleadingly presented as discrediting previous studies and their interpretation by regulators. In reality the Terhorst–Berkman analysis validates a consensus on MPP’s visibility impact that was established years before its closure, in a collaborative assessment undertaken jointly by Federal regulators and MPP’s owners.