Characteristics of Winter and Summer Aerosol Mass and Light Extinction on the Colorado Plateau

Abstract

This paper focuses on the spatial variability of fine mass and extinction budgets taking data from the winter and summer months of 1992. The study area included southern California, southern Nevada, southern Utah, Arizona, and parts of New Mexico. Two types of monitoring sites were operated: intensive and secondary or satellite. At the intensive sites, all major aerosol species were measured as well as extinction or scattering. At the satellite sites, trace elements including sulfur and hydrogen, absorption, and gravimetric fine mass were measured.

Where all aerosol species are measured, the spatial variability of extinction budgets is examined assuming an externally mixed aerosol. At the satellite sites, an approximated fine mass budget is derived and the variability of these budgets in space and time are examined. This effort was part of a study called Project MOHAVE (Measurement of Haze and Visual Effects) carried out with the principal objective of understanding the relative contribution of regional and local sources to visibility impairment on the Colorado Plateau and specifically, the Grand Canyon. Generally, the contribution of sulfates, organics, and absorption to extinction are about equal at 20-30% with the coarse mass fraction being about 10-20%. The one exception is in southern California where the nitrate contribution is significant. Furthermore, the nitrate contribution tends to be higher in the winter than summer. During the summer, concentration gradients tend to be spread out across the study area, while during the winter months, variability in concentration and budgets tends to occur on a smaller scale.