Personal exposure distribution of solar erythemal ultraviolet radiation intree shade over summer

The personal radiant exposure distribution of solar erythemal UV in tree sh ade for an upright posture was measured, with measurements over the whole s ummer for a total of 17 trees. For each tree, the personal radiant exposure distribution was measured for both the morning and afternoon periods. The exposure ratios averaged over all the trees and over the morning and aftern oon periods ranged from 0.16 to 0.49 for the different anatomical sites. A numerical model was employed to estimate the UV radiant exposure to humans in tree shade over the entire summer. The body sites with the higher exposu re ratios in the tree shade were the vertex of the head, shoulders and fore arms with radiant exposures over the summer of 1300 MED to the vertex of th e head and 1100 MED to the shoulders and forearms. These radiant exposures in the shade are substantially higher than the ambient erythemal UV measure d in full sun on a horizontal plane over a full summer at a more temperate northern hemisphere latitude. The average radiant exposures per day to each anatomical site for a complete day in the tree shade ranged from 4.6 to 14 .6 MED. This research has provided new data that is essential to quantify h uman UV exposure during outdoor activities.