Environmental Engineering Reference
In-Depth Information
with H eff = BED, E O ( O ,t) = the terrestrial spectral UV irradiance at a certain time or of
an artificial UV source, S O ( O ) = the action spectrum for a critical biological effect, e.g.,
the CIE MED spectrum, X O ( O ) = the spectral response function of the sensor, and
F = the equivalent dose of monochromatic radiation producing the same response of the
detector. H eff is given in (J/m²) eff or MED.
The same requirement holds for photosensitive films with spectral sensitivities
similar to photobiological responses (e.g., polysulphone (PS) films 31 or polycarbonate
plastics 32 ). The degree of deterioration of the detector is related to the incident UV dose.
Their signal integrates over the waveband of the radiation and over the time of
irradiation. Solid state photodiodes (e.g., GaAsP, Se or Si) in combination with optical
filters have been used as biologically weighting on-line broadband detectors 33 . For all
these radiometers, corrections by a spectral “mismatch factor” similar to Eq. 4 are
required when determining the biologically effective radiation from their readings.
The advantages of biologically weighting broadband radiometers are that they
are easy to use, if properly and regularly calibrated; they require a relatively low
investment, which allows a broad distribution; and they show a response function
similar to a biological weighting function, e.g. the CIE MED spectrum.
A comprehensive data set exists from long-term measurements at several sites, e.g., in
the United States of America and in Europe, from alpine sites, in deserts and in northern
high altitudes. PS films as simple means to continuously integrate UV exposure are
rugged, economical and can be miniaturized which enables them to a wide application
in medical context, especially as personal dosimeter.
The disadvantages of broadband radiometry lies in their response function, which
is similar, but not identical with any biological weighting function for the whole
wavelength range, e.g., of solar UV radiation. Furthermore, substantial efforts are
required concerning the precision of instrument calibration (e.g., long-term stability,
sensitivity, wavelength coverage, temperature stabilization, power consumption, data
logger capacity).
Biological UV dosimetry
The situation would be ideal, if the spectral response curve X O ( O ) of the UV
detector would be identical to the photobiological effect under consideration. This is
generally the case for biological dosimeters (Table 1) that automatically weight the
incident UV components of sunlight in relation to the biological effectiveness of the
different wavelengths and to interactions between them. In this case, in Eq. 4
S O (O) = X O ( O ) and H eff is given by the following simple relation:
(5)
H eff
F
with F = the equivalent dose of monochromatic radiation producing the same response
of the biodosimeter as the radiation under consideration. H eff is given in (J/m²) eff
7
. In
most cases, O = 254 nm has been used as reference wavelength. This is based on the fact
that this wavelength lies in the absorption maximum of DNA and on its availability as a
sharp line from low pressure mercury lamps.
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