Spatial and Temporal Patterns in Particle Data Measured During the MOHAVE Study

Project MOHAVE (Measurement of Haze and Visual Effects) was conducted during 1992 to assess the contribution of the Mohave Power Project, other point sources, and regional emissions to visibility impairment in Grand Canyon National Park. One objective of Project MOHAVE was to determine the spatial and temporal patterns of aerosol concentrations during summer and winter in the region. Patterns in the fine particle data were examined by time plots, spatial contour maps, and empirical orthogonal function (EOF) analysis, which reduces all observed spatial patterns to a few that explain most of the variance. Results obtained during the summer differed from those obtained in the winter. However, differences were not uniform across species. During the summer there was evidence of transport of sulfur, organic and light-absorbing carbon, and several trace elements from southern California into the study area. Winter concentrations of several species, including sulfur, selenium, and organic and light-absorbing carbon, were higher within the canyon than on the rim, probably because emissions from local sources stagnate within the canyon during the winter. Sources in and near Las Vegas, NV, influenced the concentrations of several species, especially at sites to the north and east.