,+rmosphmic zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Emr ir onmellt VOI. 15. NO. 10/l I. pp. XX-20%1981 00066981j81/ 102@ 43--12 SK?.WJiO Pnnt cd m Great Britain. $ 1981 Pergamon Press Ltd. zyxwvutsrqpon REGIONAL ANALYSIS OF FACTORS AFFECTING VISUAL AIR QUALITY* ANN PITCHFORD, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA MARC PITCHFORD+ and WILLIAM MALM Enviro~me~taI Mon~t~~ng Systems Laboratory, U.S. Env~ro~men~l Prot~tjo~ Agency, Las Vegas, Nevada, U.S.A. ROBERT FLOCCHINI and THOMAS CAHILL University of California, Davis, California, U.S.A. and ERIC WALTHER Visibility Research Center, John Muir Institute, Las Vegas, Nevada, U.S.A. (First received 16 September 1980 and i~~nul~orm 2 February 1981) Abstract-The U.S. Environmen~l Protection Agency, National Park Service, Visibility Research Center, and University of California at Davis are currentty operating a monitoring program in national parks and monuments throughout much of the weatern United States. Project VIEW, the Visibility Investigative Experiment in the West, includes measurement of visibility parameters using manual telephotometers, and m~urement of particle concentrations averaged over 72 h. Variation of these parameters occurs in both space and time. To better understand these variations, several techniques including principal component analysis and data comparisons among sites are applied to Fall, 1979 data for much of the network. Then the Grand Canyon is chosen for additional analysis. Best and worst case visibility days are determined and compared with particle concentrations. Finally, hypothetical causes for visibility reduction are further verified by computing wind trajectories back in time for these special case days. Highlights of this preliminary inv~ti~tjon include evidence that fine sulfur and fine particles are responsible for visibility variation at the VIEW sites; that fine particle copper may be suitable as a tracer for copper smelter impact and that at the Grand Canyon, the majority of trajectories for days of visibility greater than 310 km come from the north and west, over Utah and Nevada. In recent years an awareness has developed of the potential conflict in the western United States between accelerated resource development and increased population, and maintenance of the high degree of visua1 air quality traditionally associated with the West. This has resulted in increasing interest in dete~ining the role of various air pollution sources in visibility degradation. As more has been learned about the causes of visibility degradation, questions about regional scale visibility phenomena have developed. To answer them, it is necessary to establish the spatial and temporal characteristics of regional phenomena and to evaluate the relative impact of both nearby and distant sources on visibility. In an effort to answer these questions the U.S. EPAs Environmental Moni- toring Systems Laboratory-Las Vegas (EMSL-LV) in cooperation with the National Park Service, estab- lished project VIEW, Visibility Investigative Experi- ment in the West. This regional scale visibility moni- toring and particle sampling network is located in national parks and monuments throughout the Southwest. * Paper presented at the Symposium on Plumes and Visibility: Measurements and Model Components. Grand Canyon, Arizona, U.S.A. 10-14 November 1980. t On assignment from National Oceanic and Atmospheric Administration. The following presentation is a preliminary analysis of some of the visibility and fine particulate data gathered during the initial phases of VIEW. The investigation starts by applying statistical techniques including principal component analysis to the Fall, 1979 visibility and particle data set. Next, temporal variations of visual range at eight of the monitoring sites are compared. Then, the Grand Canyon is chosen for more detailed analysis, and best and worst visibility days are identified for comparison with particle ~on~ntrations. Possible causes for visibility reduction are further verified by computing wind trajectories for the several days preceding these best and worst days. The telephotometer network is operated by the Visibility Research Center, John Muir Institute, af- filiated with the university of Nevada, Las Vegas. A description of the network locations, operating procedures, and data handling techniques is given by Malm et af. (1980) and Maim (1980). Briefly, instan- taneous measurements of contrast between targets and the sky at a wavelength of 550 nm (green) are made three times daily, 9 a.m., noon and 3 p.m. local time, using a manual MRI Vista RangerTM telephotometer. These data are available from the summer of 1978 to the fall of 1979, in the form of standard visual ranges calculated for each tree-covered ;arget sight path at each monitoring site. Standard visual range is visual 2043