RESPONSE TO UV-B RADIATION: WEIGHTING FUNCTIONS AND ACTION SPECTRA - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 88

reciprocal photons per square meter and per second) are the spectral biological
weighting function for UV and the average biological weighting factor for PAR,
respectively. As previously determined biological weighting functions showed a marked
difference in slope in the UV - B as compared to UV - A, the analytical continuous
function representing H UV (O) was chosen formed by two different exponential
functions: the first one from 285 nm to a wavelength O 0 and the second from O 0 to 400
nm, the wavelength O 0 (285 nm < O 0 < 400 nm) being a free parameter of the fitting
procedure. To avoid discontinuity in the UV, the constraint that the two functions had
the same value at O 0 was used. The best fit, obtained by means of an iterative process
based on the least-squares method, returned the value of 331 nm for O 0 and yielded the
following components for the biological weighting function (see Fig. 4):
H UV (O) = 6.1164u10 15 ue -0.12uO 285 nm < O < 331 nm

H UV (O) = 3.235u10 3 ue -0.0346uO

331 nm < O < 400 nm

H PAR = 3.17u10 -4 400 nm < O < 700 nm

1E+01

1E+00

1E-01

1E-02

1E-03

280 300 320 340 360 380 400

Wavelength [nm]

Figure 4. Biological weighting functions for the inhibition of the chlorophyll fluorescence parameter
'F/Fm' in D. salina (redrawn from reference 12).

This biological weighting function for the UV inhibition of photosynthesis in
D. salina shows quite a good agreement, both in shape and absolute magnitude, with
that determined for the microalga Phaeodactylum . 27