Atmospheric Chemistry and Physics Discussions
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10.5194/acpd-8-781-2008
http://www.atmos-chem-phys-discuss.net/8/781/2008/
http://www.atmos-chem-phys-discuss.net/8/781/2008/acpd-8-781-2008.html
http://www.atmos-chem-phys-discuss.net/8/781/2008/acpd-8-781-2008.pdf
781
796
2008-01-16
Utilising shade to optimize UV exposure for vitamin D
D. J. Turnbull
turnbull@usq.edu.au
A. V. Parisi
Centre for Rural and Remote Area Health, University of Southern Queensland, Toowoomba, Queensland 4350, Australia
Numerous studies have stated that humans need to utilise full sun radiation,
at certain times of the day, to assist the body in synthesising the required
levels of vitamin D<sub>3</sub>. The time needed to be spent in the full sun
depends on a number of factors, for example, age, skin type, latitude, solar
zenith angle. Current Australian guidelines suggest exposure to
approximately 1/6 to 1/3 of a minimum erythemal dose (MED), depending on
age, would be appropriate to provide adequate vitamin D<sub>3</sub> levels. The
aim of the study was to determine the exposure times to diffuse solar UV to
receive exposures of 1/6 and 1/3 MED for a changing solar zenith angle in
order to assess the possible role that diffuse UV (scattered radiation) may
play in vitamin D<sub>3</sub> effective UV exposures (UV<sub>D3</sub>). Diffuse and
global erythemal UV measurements were conducted at five minute intervals
over a twelve month period for a solar zenith angle range of 4° to
80° at a latitude of 27.6° S. For diffuse UV exposures of 1/6 and
1/3 MED, solar zenith angles smaller than 60° and 50° respectively
can be utilised for exposure times of less than 10 min. Spectral
measurements showed that, for a solar zenith angle of 40°, the UVA
(315–400 nm) in the diffuse component of the solar UV is reduced by
approximately 62% compared to the UVA in the global UV, whereas UV<sub>D3</sub>
wavelengths are only reduced by approximately 43%. At certain latitudes,
diffuse UV under shade may play an important role in providing the human
body with adequate levels of UV<sub>D3</sub> (290–330 nm) radiation without
experiencing the high levels of damaging UVA observed in full sun.
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