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AVERAGE ANNUAL SOLAR UV DOSE OF THE CONTINENTAL US CITIZEN
Citation:
Godar, D. E., S. P. Wengraitis, J H. Shreffler, AND D. Sliney. AVERAGE ANNUAL SOLAR UV DOSE OF THE CONTINENTAL US CITIZEN. Presented at 13th International Congress on Photobiology, San Francisco, CA, July 2-6, 2000.
Impact/Purpose:
To understand and characterize the factors, including optical transmission properties of aerosols, which affect the intensity of UV-B radiation measured at the earth's surface in order to improve our estimates of ecosystem and human exposures to UV-B radiation; to understand the relationship between UV radiation and total column ozone; to model UV-B exposures at different locations, conditions, and times in order to estimate UV-B exposures throughout the US. This objective is achieved by maintaining a strict quality assurance program for both the Brewer Spectrophotometers in the network and the UV data obtained from the Brewers.
Description:
The average annual solar UV dose of US citizens is not known, but is required for relative risk assessments of skin cancer from UV-emitting devices. We solved this problem using a novel approach. The EPA's "National Human Activity Pattern Survey" recorded the daily outdoor-activity profiles over the course of two years for about 10,000 continental US citizens to assess exposure to environmental pollutants, one of which is UV radiation. From that survey, we extracted only the daylight-hour data of the northern and southern indoor workers subdividing by seasons, sex, and age (0-21, 22-59, and 60+) to find the average time Americans spend outdoors in each group. Using the ambient percentage for indoor workers found by the Dutch (2.5%; H. Slaper thesis, 1987) to standardize our northeastern data, we found their actual UV-exposure time was about one-third their total daylight-time outdoors. Of the total available solar UV, the average US citizen's ambient percentages are as follows: northern females 2.67% and males 3.54%, southern females 2.56% and males 3.79%. We then calculated their average annual solar UV dose, excluding vacation, using seasonal averages from measurements made over two years by EPA Brewer spectrophotometers located in the four quadrants of the US: Atlanta, GA, Boston, MA, Bozeman, MT and Riverside, CA. Including a conservative three-week vacation in the continental US, i.e., 30% country, 30 % beach, 30% sight-seeing and 10% home, the estimated average annual solar UV doses are as follows: northern females 28,361 J/m2 and males 32,479 J/m2, southern females 33,215 J/m2 and males 39,834 J/m2. The average annual solar UV dose for the continental US citizen is 25,169 + vacation (9,178), or 34,347 J/m2 (343 SED or 137 MED, MED=250 J/m2). Thus, we can now assess the relative increased risk of skin cancer from UV-emitting devices for the continental US citizen.
This work has been funded in part by the United States Environmental Protection Agency. It has been subjected to Agency Review and approved for publication.