Solar ultraviolet exposures at ground level in tree shade during summer insouth east Queensland

Data are presented on the effect of the tree canopy transmittance in the vi sible waveband (V-T), canopy width, height and height of the start of the t ree canopy (C-H) on the solar UV in tree shade on a horizontal plane at gro und level during a Southern Hemisphere summer. Of these factors, the V-T an d C-H have an influence on the UV irradiances in the tree shade. The shade ratios (UV in tree shade to that in full sun) for erythemal UV ranged from 0.71 to 0.42, 0.54 to 0.29 and 0.63 to 0.41 for morning, noon and afternoon , respectively, for the V-T range of 0.4-1.0. Over the same V-T range, the shade ratios for UVA ranged from 0.61 to 0.28, 0.50 to 0.22 and 0.49 to 0.2 9 for morning, noon and afternoon, respectively. The UV exposures in the tr ee shade decreased with the V-T with a marginally higher decrease in the ir radiances for the UVA compared to the erythemal UV. Despite the protection by the tree shade, significant UV in the tree shade of approximately 4 MED (minimum erythemal dose) were received for the latitude in this research on a cloud free summer day on a horizontal plane over a 2-h period centred ab out solar noon.