Maps are prepared which illustrate median, mid-day visibility levels in suburban/nonurban locations of the continental United States. Median visibilities at 94 locations are determined from cumulative frequency distributions of quality-checked airport observations. Seven locations in the Southwest with photographic photometry or nephelometry data (which agree quite well with the airport data) are also included. The spatial pattern of visibility is demonstrated with isopleth maps for both the annual medians and summertime medians during the years 1974-1976.

EPA project officer: John Bachmann, William E. Wilson, and Thomas G. Ellestad. Prepared by Technology Service Corporation. "September 1979." Interim report. Includes bibliographical references (page 26). "EPA-450/5-79-010."

Maps are prepared which illustrate median, mid-day visibility levels in suburban/nonurban locations of the continental United States. Median visibilities at 94 locations are determined from cumulative frequency distributions of quality-checked airport observations. Seven locations in the Southwest with photographic photometry or nephelometry data (which agree quite well with the airport data) are also included. The spatial pattern of visibility is demonstrated with isopleth maps for both the annual medians and summertime medians during the years 1974-1976. The consistency of the spatial gradients in visibility and the agreement between neighboring locations attest to the quality of the visibility data. The isopleth maps reveal that the best visibility (70+ miles) occurs in the mountainous Southwest. Visibility is also quite good (45 - 70 miles) north and south of that region, but sharp gradients occur to the east and west of that region. Most of the area east of the Mississippi and south of the Great Lakes exhibits median visibilities of less than 15 miles annually and less than 10 miles during the summertime.