title: Comparison between seasons of the ultraviolet environment in the shade of trees in Australia.
abstract: OBJECTIVE
  This paper has considered the erythemal UV (UVery), UVA and visible irradiances in the shade of Australian trees for each season at a sub-tropical southern hemisphere site.
  
  
  METHODS
  The irradiances in tree shade have been measured with radiometers as a percentage of the irradiances in the sun for each season of the year.
  
  
  RESULTS
  Although the solar irradiances are lower in winter, the percentages of the UV in tree shade compared to the UV in full sun are marginally higher (by up to 7%) in the winter compared to summer. The range of percentages for UVery was up to double that of the percentages of the visible waveband. The percentages for UVery were also higher than for the UVA waveband. The percentages of the irradiances in the tree shade compared to full sun are 8-14% lower at noon compared to the morning and afternoon for the UVery waveband. The ratio of UVA to UVery is lower in the tree shade compared to the full sun.
  
  
  CONCLUSIONS
  The UVA to UVery ratio is expected to be even lower in the tree shade as a result of ozone depletion. This, combined with the visible irradiances in the tree shade not being a reliable indication of the biologically damaging UV irradiances, has consequences for public health and skin cancer prevention.
authors.affiliation: Centre for Astronomy and Atmospheric Research, Faculty of Sciences, University of Southern Queensland, Toowoomba, Australia.
authors.forename: A V
authors.initials: AV
authors.lastname: Parisi
authors.forename: J C
authors.initials: JC
authors.lastname: Wong
authors.forename: M G
authors.initials: MG
authors.lastname: Kimlin
authors.forename: D
authors.initials: D
authors.lastname: Turnbull
authors.forename: R
authors.initials: R
authors.lastname: Lester
mesh_terms: D001315:Australia; D004890:Erythema / Q000209:etiology; D006801:Humans; D011874:Radiometry; D012621:Seasons; D013472:Sunlight; D014197:Trees; D014466:Ultraviolet Rays