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Estimation of Pedestrian Level UV Exposure Under Trees

Authors

  • Richard H. Grant,

    Corresponding author
    1. Department of Agronomy, Purdue University, W. Lafayette, IN
      *To whom correspondence should be addressed at: Department of Agronomy, 1150 Lilly Hall, Purdue University, W. Lafayette, IN 47907-1150, USA. Fax: 765-496-2926; rgrant@purdue.edu
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  • Gordon M. Heisler,

    1. USDA Forest Service, Northeastern Research Station, 5 Moon Library, c/o State University of New York College of Environmental Science and Forestry, Syracuse, NY
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  • Wei Gao

    1. USDA UVB Monitoring Program, Natural Resources and Ecology Laboratory, Colorado State University, Fort Collins, CO
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  • Posted on the web site on January 28, 2002.

*To whom correspondence should be addressed at: Department of Agronomy, 1150 Lilly Hall, Purdue University, W. Lafayette, IN 47907-1150, USA. Fax: 765-496-2926; rgrant@purdue.edu

ABSTRACT

Trees influence the amount of solar UV radiation that reaches pedestrians. A three-dimensional model was developed to predict the ultraviolet-B (UV-B) irradiance fields in open-tree canopies where the spacing between trees is equal to or greater than the width of individual tree crowns. The model predicted the relative irradiance (fraction of above-canopy irradiance) under both sunlit and shaded conditions under clear skies with a mean bias error of less than 0.01 and a root mean square error of 0.07. Both model and measurements showed that the locations people typically perceive as shady, low-irradiance locations in the environment can actually have significant UV-B exposure (40–60% of that under direct sunlight). The relationship of tree cover in residential neighborhoods to erythemal UV-B exposure for children and adults was modeled for the 4 h around noon in June and July. Results showed that human exposures (on the horizontal) in cities located at 15 and 30° latitudes are nearly identical. For latitudes between 15 and 60°, ultraviolet protection factors (UPF) were less than 2 for less than 50% tree cover. A UPF of 10 was possible at all latitudes for tree cover of 90%.

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