Vitamin D production in human skin occurs only when UV radiation exceeds a threshold. From simulations of UV irradiances, the VitD-ez www page computes the daily duration of dermal vitamin D production at midday when UV radiation exceeds the required threshold. The VitD-ez www page is a simplified version of the more complex VitD web page ( https://fastrt.nilu.no/VitD.html). The simplified VitD-ez www page is convenient for users unfamiliar to radiative transfer modelling, because the model input is limited and more intuitive.
The sky conditions in the simple VitD-ez www page are somewhat different than the complex VitD web page. "Cloudless" is a very clear, pristine atmosphere with an aerosol turbidity coefficient (Ångström β) of 0.02. "Scattered clouds" in VitD-ez correspond indeed to scattered clouds in the VitD complex version, but with a cloud fraction of 30%. "Broken clouds" in the VitD-ez version are not "broken clouds with radiation enhancement" as in the VitD version, but are scattered clouds like the previous with a cloud fraction of 70%. "Overcast" in Vit D-ez is the same as in the complex VitD version. For all cloudy scenarios in VitD-ez, the cloud liquid water column is set to 240 g m-2.
Ozone layer thicknesses of "Thin", "Medium" and "Thick" refer to ozone columns of 200, 350 and 500 DU, respectively. DU = Dobson unit (1 DU = 1matm-cm, equivalent to the thickness of 0.01 mm of pure ozone at standard conditions of temperature [273.15K] and pressure [1013.25 Pa]).
All other values should be self-explanatory, and agree with the more complex VitD page.
Author: Ola Engelsen
Norwegian Institute for Air Research
Copyright © 2005 Ola Engelsen
Last modified September 20th 2006.
The current model has undergone internal checking and validation. If you have any questions or comments on this service and how it could be improved for your needs, please contact the author.
If you use this program and publish the results, I would appreciate a lot if you cite it:
Ola Engelsen, Magritt Brustad, Lage Aksnes and Eiliv Lund (2005) Daily Duration of Vitamin D Synthesis in Human Skin with Relation to Latitude, Total Ozone, Altitude, Ground Cover, Aerosols and Cloud Thickness, Photochemistry and Photobiology, 81(6), 1287-1290.
A reprint is freely available at http://www.nilu.no/index.cfm?ac=publications&folder_id=4309&publication_id=9024&view=rep.
The underlying simulations are done using the following model:
Engelsen O. and Kylling A., Fast simulation tool for ultraviolet radiation at the Earth's surface. Optical Engineering, 44 (4), 041012 (2005).
This model interface has mostly the same input options as the VitD web tool.
Brustad, M., E. Alsaker, O. Engelsen, L. Aksnes, and E. Lund (2004) Vitamin D status in middle-aged women at 65-71 °N in relation to dietary intake and exposure to ultraviolet radiation. Publ. Health Nutr. 7, 327-335.