Regional and local determinations of particulate matter and visibility in the southwestern United States during June and July, 1979

Data on ambient particulate concentrations by size and elemental composition taken in Arizona and Utah are compared to simultaneous telephotometer measurements of standard visual range. Particulate samples were collected during the VISTTA program from 26 June to 11 July 1979, at Zilnez Mesa, Arizona, and compared to similar 24 h measurements made as part of a long term research program at Zion and Canyonlands National Parks in Utah. Samples were collected with rotating drum Multtday impactors which provide three aerodynamic size ranges; 15μm-3.5μm; 3.5μm-0.5μm, and less than 0.5/jm. Elemental composition of samples was measured using the particle induced X-ray emission (PIXE) system at the Crocker Nuclear Laboratory. Measurements of visibility were made at Canyonlands National Park and Zilnez Mesa using both multiwavelength telephotometers and nephelometers. Results indicate that the particulate matter in each size range behaves to a large degree independently of the other size ranges, but that correlations are often observed between sites. On 29 June, an episode of elevated sulfur concentrations, > 1 μm m −3 of S, was observed at all three sites. Decreased visibilities were recorded for the episode period at both Canyonlands and Zilnez Mesa. Sulfur episodes on 22-24 June and 20-21 July measured at Zion and Canyonlands also correlated well with reduced visibility at Canyonlands. Episodes of reduced visibilities also occurred during periods of stable sulfur values. The strongest of these, on 1718 June, as well as a weaker one, 4-7 June, correlated well with fine soils in the 0.5-3.5 μm size range. The conclusion is that reduced visibility is associated with regional episodes of both increased sulfur and increased fine soils, with best correlations occurring in both cases for sizes somewhat greater than 0.5μm dia.