QUANTIFICATION OF BIOLOGICAL EFFECTIVENESS OF UV RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 51

Time terrestrial (min)

0 50 100 150 200

10 0

10 -1

10 -2

10 -3

10 -4

0,0 0,5 1,0 1,5

Time extraterrestrial, min

Figure 2 . Survival of spores of Bacillus subtilis after exposure to extraterrestrial solar radiation
(>190 nm) during the Spacelab 1 mission (solid line) or to global UV radiation at the surface of the
Earth around noon in San Francisco area (37.5°N 122.2°W) on 10.8. 1985) (dashed line) (data
modified from ref. 12).

stratospheric ozone layer effectively absorbs UV radiation at wavelengths shorter than
290 nm 17 . However, a decrease in total column ozone would shift the edge of the solar
spectrum on Earth towards shorter wavelengths (Figure 1).
In order to determine the biological effectiveness of environmental UV radiation,
spectral data are multiplied with an action spectrum of a relevant photobiological
reaction 18 . The result is a biological effectiveness spectrum (Figure 1). It weights the
environmental UV radiation according to the biological effectiveness at the different
wavelengths. The biologically effective irradiance E eff is then determined as follows:
O

(1)

E eff ³

E O O S O d

O

with E O ( O ) = the solar spectral irradiance and S O ( O ) = the spectral sensitivity or action
spectrum for a critical biological effect. E eff is given in (W/m²) eff .
There are in general three different approaches to quantify a biologically
effective solar irradiance. These are: (i) weighted spectroradiometry where the
biologically weighted radiometric quantities are derived from physical solar spectral
data by multiplication with an action spectrum of a relevant photobiological process
according to equation (1); (ii) wavelength integrating chemical-based or physical
broadband radiometers with spectral sensitivities similar to a biological response
function; and (iii) biological dosimeters that directly weight the incident UV
components of sunlight in relation to their biological effectiveness and to interactions
between them. These different approaches of biologically weighted UV dosimetry are
discussed in the following.