Berit Kjeldstad

SUSPEN intercomparison of ultraviolet spectroradiometers

Results from an intercomparison campaign of ultraviolet spectroradiometers that was organized at Nea Michaniona, Greece July, 1–13 1997, are presented. Nineteen instrument systems from 15 different countries took part and provided spectra of global solar UV irradiance for two consecutive days from sunrise to sunset every half hour. No data exchange was allowed between participants in order to achieve absolutely independent results among the instruments. The data analysis procedure included the determination of wavelength shifts and the application of suitable corrections to the measured spectra, their standardization to common spectral resolution of 1 nm full width at half maximum and the application of cosine corrections. Reference spectra were calculated for each observational time, derived for a set of instruments which were objectively selected and used as comparison norms for the assessment of the relative agreement among the various instruments. With regard to the absolute irradiance measurements, the range of the deviations from the reference for all spectra was within ±20%. About half of the instruments agreed to within ±5%, while only three fell outside the ±10% agreement limit. As for the accuracy of the wave-length registration of the recorded spectra, for most of the spectroradiometers (14) the calculated wavelength shifts were smaller than 0.2 nm. The overall outcome of the campaign was very encouraging, as it was proven that the agreement among the majority of the instruments was good and comparable to the commonly accepted uncertainties of spectral UV measurements. In addition, many of the instruments provided consistent results relative to at least the previous two intercomparison campaigns, held in 1995 in Ispra, Italy and in 1993 in Garmisch-Partenkirchen, Germany. As a result of this series of intercomparison campaigns, several of the currently operating spectroradiometers operating may be regarded as a core group of instruments, which with the employment of proper operational procedures are capable of providing quality spectral solar UV measurements.

AN ACTION SPECTRUM FOR BLUE AND NEAR ULTRAVIOLET IN ACTIVATION OF Propionibacterium acnes; WITH EMPHASIS ON A POSSIBLE PORPHYRIN PHOTOSENSITIZATION

—Propionibacterium acnes (P. acnes), grown on Eagles medium with different pH. were irradiated with monochromatic light in the range 320 to 440 nm. Different pH leads to different porphyrin concentrations in the cells. The light sensitivity of the bacteria was estimated from the reduction in their ability to form colonies after radiation. The sensitivity was highest for the lowest wavelength (320 nm). and decreased continuously with increasing wavelength up to 380 nm. In the region between 380 and 440 nm there was a second maximum (at 415 nm) which corresponds to the maximum absorption ol the fluorescing porphyrins in P. acnes. The sensitivity to 415 nm light was found to be dependent on the endogenous porphyrin concentration in the cells. while the sensitivity to 320 nm radiation was independent of the amount of porphyrin present. These results indicate that porphyrins produced by the bacteria are important for the light sensitivity of these bacteria.

Variability of UV Irradiance in Europe

The diurnal and annual variability of solar UV radiation in Europe is described for different latitudes, seasons and different biologic weighting functions. For the description of this variability under cloudless skies the widely used one‐dimensional version of the radiative transfer model UVSPEC is used. We reconfirm that the major factor influencing the diurnal and annual variability of UV irradiance is solar elevation. While ozone is a strong absorber of UV radiation its effect is relatively constant when compared with the temporal variability of clouds. We show the significant role that clouds play in modifying the UV climate by analyzing erythemal irradiance measurements from 28 stations in Europe in summer. On average, the daily erythemal dose under cloudless skies varies between 2.2 kJ m−2 at 70°N and 5.2 kJ m−2 at 35°N, whereas these values are reduced to 1.5–4.5 kJ m−2 if clouds are included. Thus clouds significantly reduce the monthly UV irradiation, with the smallest reductions, on average, at lower latitudes, which corresponds to the fact that it is often cloudless in the Mediterranean area in summer.

Fluorescence from pilosebaceous follicles

SummaryFluorescence studies were performed on the extrusions from pilosebaceous follicles. Pressure extractions produced follicle samples which showed fluorescence under Woods light. The samples were then analysed in a fluorometer giving corrected excitation spectra.The structured emission spectra achieved were interpreted as being due to porphyrins produced by Propionibacterium acnes (P. acnes). Details in the spectra showed close resemblance to spectra from cultured P. acnes cells. The emission spectra showed distinct features in all the four subjects investigated (who were different with respect to age, sex, follicle sampling area, and tendency to acne) and dominant peaks due to at least three porphyrins were found. The concentrations of these porphyrins vary from case to case. Excitation spectra were recorded and supported the assumption that the fluorescent emission was partly due to coproporphyrins and metalloporphyrins in the samples. Free protoporphyrins did not seem to be present in the extrusions. The excitation spectra, in particular, vary from person to person but seem to be constant over time in one and the same subject.

DIFFERENT PHOTOINACTIVATION MECHANISMS IN Propionibacterium acnes FOR NEAR‐ULTRAVIOLET and VISIBLE LIGHT

The light sensitivity of Propionibacterium acnes was investigated when the cells were exposed to anoxia, sodium azide, D2O or superoxide dismutase in combination with visible light (broad band red light and 415 nm) and near‐ultraviolet irradiation (360 and 320 nm). During anoxia the cells became less sensitive when the irradiation wavelength increased. Oxygen increased the photodamage to a greater extent in the case of visible light than of near‐UV light. The photosensitization effects were, however, more or less oxygen dependent at all wavelengths used. An effect of azide and D2O on the light sensitivity was observed for visible light, while superoxide dismutase was effective only at 320 nm.

Europe's darker atmosphere in the UV-B

Irradiation in the ultraviolet wavelength range is found to be up to 50% lower in the European summer compared to sites with comparable latitudes in New Zealand. We have developed a method to quantitatively attribute the causes for such differences between sites by analysis of spectra. We conclude that these large differences are caused mainly by differences in total ozone, cloudiness, aerosol loading and Sun-Earth separation. The relative contribution of clouds varies from year to year and it is site dependent. Averaged over several years we find a strong latitudinal gradient of the cloud impact within Europe, with much less cloud attenuation in southern Europe. Due to the differences in total ozone and aerosol loading, the UV-B levels are generally lower in Europe compared to New Zealand. It is likely that inter-hemispheric differences will change in coming decades due to a combination of changes in ozone concentrations, air pollution and cloudiness as a result of climate change. However, since the future evolution of these major parameters is highly uncertain, the magnitude and even the sign of such changes are not known yet.

Porphyrin Photosensitization of Bacteria

In the present study we focus our attention on the gram positive bacterium P. acnes. It is located on the human skin and normally produces large amounts of porphyrins, both copro- and protoporphyrin (Fanta et al. 1981, Kjeldstad et al. 1984, Lee et al. 1978). The bacteria can be visualized on the skin by their strong, red porphyrin fluorescence, in near UV-light (Mc Ginley et al. 1980). It is of interest to study possible photosensitivity of P.acnes due to these internally produced porphyrins. Investigations of the possible effects of externally added porphyrins, e.g. Hpd, could also be useful in a broader context since Hpd is used as a sensitizer in photodynamic therapy of certain cancer forms (Dougherty et al. 1978). Therefore it is desirable to study the detailed light reactions involved in Hpd photosensitization in a variety of cellular systems. Studies of bacterial photosensitization may also adress the question on whether phototherapy of infections is feasible.

All-weather ultraviolet solar spectra retrieved at a 0.5-Hz sampling rate

A measurement scheme and an algorithm have been developed to retrieve global irradiance ultraviolet solar spectra (290-400 nm) at a sampling rate of 0.5 Hz. The algorithm combines spectral irradiance measurements performed with a slow (a few minutes) scanning spectroradiometer (Optronic Model OL752) and a moderate bandwidth multichannel radiometer (Biospherical ground-based ultraviolet radiometer Model 541). The filter radiometer instrument allows for continuous observations of global UV radiation at five channels (approximately 10-nm bandwidth), performed simultaneously with spectral measurements. Information about changing cloud conditions during a spectral scan was retrieved from filter measurements and applied to spectral data, hence estimated spectra without cloud variations could be constructed. The quality of the estimated spectra depends on data quality from both instruments. The method works well in all kinds of weather conditions, as long as the Sun is above the horizon and none of the instruments are hampered by measurement errors.

Near-UV-induced radicals in Propionibacterium acnes, studied by electron spin resonance spectrometry at 77 K.

Suspensions of Propionibacterium acnes were UV irradiated and the induced radicals were measured at 77 K by electron spin resonance (ESR) spectrometry. Two types of radical were formed during irradiation and stabilized in the frozen suspensions. The relative yield of each radical was studied as a function of irradiation wavelength. The first radical, which was a singlet with a peak-to-peak width of 20 G, was insensitive to the deoxygenation of the samples and to the exchange of solvent water by heavy water. The action spectrum was similar to the absorption spectrum of NADPH. The second type of radical was not formed in deoxygenated samples and the shape of the ESR spectrum was characteristic of the superoxide radical. This radical was only formed at wavelengths below 340 nm.

Comparison of solar UV measurements performed with spectroradiometer and moderate bandwidth multichannel radiometer for different cloud conditions

A method to control spectral global irradiance data using moderate bandwidth multichannel radiometer data was analyzed. The multichannel instrument sampled at both 1 min averages and a high frequency of approximately 0.5 Hz simultaneously with the spectral data. Deviations between multichannel radiometer and spectroradiometer, caused by different angular response (cosine and azimuth), were investigated. Uncertainties due to separate sampling systems and nonideal timing were quantified and removed before data intercomparison. It is shown that high-frequency multichannel measurements, ideal synchronized to spectral measurements can be used to identify short-term unexpected errors in spectral measurements down to a level of 5%, limited by the relative angular response error between the instrument during variable cloud conditions.