Pollution Sources Over the Grand Canyon and Canyonlands National Parks

To investigate pollution sources that are degrading the visibility of two national parks, Grand Canyon National Park, AZ, and Canyonlands National Park, UT, daily samples of total suspended particulates (TSP), PM2.5, trace gases, and organic compounds were collected in the two parks in the summer (July) of 2001 and winter (December-January) of 2001-2002. Factor analysis results show a number of anthropogenic signals (e.g., smelters) in the summer air over the Grand Canyon. In winter, the Grand Canyon samples revealed an aged pollution signal, which was probably transported from long distance, and a local source. In contrast, Canyonlands has less distinctive pollution signals in summer compared with winter. Summer air there shows an aged pollution source, evidence for smelter impacts on the concentrations of rare-earth elements and other metals, and a titanium source. More individual pollution signals were identified from the winter samples at Canyonlands (e.g., coal combustion and smelters). Our chemical and meteorological data clearly indicate that the main long-range transport pathway for pollution in summer is via southwesterly winds at both national parks; this implicates western Arizona as a likely source region. In winter pollution comes from the Salt Lake area via northerlies or northwesterlies.