ABSTRACT

Sheets of polysulphone film have been extensively used as detectors to monitor solar UVB radiation. The advantages of polysulphone detectors are that they are small in size, they have good thermal stability and they are sensitive to UVB radiation. The principal disadvantage of polysulphone detectors is that their spectral sensitivity includes part of the short-wavelength UVA. In this study, we investigate the spectral sensitivity of the polysulphone detector with a series of monochromatic (+ or -2 nm) excitations. We then compare the polysulphone-effective solar radiation with the erythemally effective solar radiation by comparing solar UVB data obtained with polysulphone films with those obtained with a spectroradiometer. From polysulphone data on the seasonal variation of solar UVB radiation, we estimate the corresponding fluctuations of the absorption of the ozone layer. We show that the spectral sensitivity of the polysulphone film is closer to the erythema action spectrum than that indicated by earlier data and that polysulphone detectors can be used to predict the erythema risk of solar UVB. Measurements on solar UVB with polysulphone films and with a spectroradiometer were found to be strongly correlated (R^sup 2^ > 0.95). Finally, polysulphone-based measurements provide a good measure of the fluctuations of the stratospheric ozone layer.

INTRODUCTION

Solar UVB refers to the wavelength range of 290-320 nm of solar UV radiation. This range of wavelengths can induce sunburn in human skin. The relative contributions of different wavelengths to the sunburn reaction may be determined from the erythema action spectrum. Because the erythema action spectrum drops rapidly from 290 to 320 nm and the solar spectrum increases almost exponentially from 290 to 320 nm, it is difficult to evaluate the erythemally effective solar radiation without carrying out an integration of the product of these two functions. UVB detectors with spectral sensitivity that mimics the erythema action spectrum would provide us an accurate measure of the risk for producing a sunburn reaction with exposure to solar radiation. Polysulphone films (40 [mu]m) have been proposed as such a detector (1,2).

The structure of polysulphone contains many aromatic rings (Fig. 1), which are responsible for the strong absorption in the UV region. It has been found that the absorbance of a polysulphone film, particularly near 330 nm, increases with exposure to UV radiation because of the formation of conjugated [pi]-electron systems. The change in absorbance of the polysulphone film at 330 nm ([Delta]A^sub 330^) has been used to estimate UVB fluence because there exists a monotonie relation between UV doses and [Delta]A^sub 330^ (1-10). Polysulphone film as a personal environmental UV monitor has the advantage of good stability to thermal radiation, humidity and high-energy radiation (7-8).

The sensitivity for the change in 330 nm absorbance of polysulphone films is higher in the UVB than in the UVA (1-2). The previously published polysulphone sensitivity spectrum resembles the erythema action spectrum with a significant redshift. The sensitivity of polysulphone to UVA constitutes a negative factor because the longer wavelengths have a proportionally larger contribution in the solar spectrum; therefore, the polysulphone film response would tend to exaggerate the risk of solar UVB in the environment. Spectroradiometric measurements with a double monochromator provide the most accurate information about contributions from different wavelengths of the solar spectrum; it is important to correlate measurements with polysulphone film detector response to those with a spectroradiometer in order to validate polysulphone film as a solar UVB dosimeter.

Polysulphone film detectors have been used as personal monitors to measure diurnal and seasonal variations of solar UVB (8). In a previous study, we determined the diurnal and seasonal variations of the solar UVB at the latitude of 29.5[degrees]N with polysulphone films (8). Solar UVB showed a sinusoidal relation with the time of year. The seasonal variation of solar UVB is also influenced by stratospheric ozone absorption. The sharp increase in the short-wavelength part of the solar UV spectrum coincides with the cutoff part of the stratospheric ozone absorption band. So, the question arises whether we can measure with polysulphone-based detectors the effects of fluctuations of the ozone layer on the terrestrial environment.

In this study, we reexamined the polysulphone sensitivity spectrum by exposing films to narrowband monochromatic sources. The calibration was performed based on the dose-response curve for each wavelength. We investigated the possibility of using polysulphone film as a solar UVB dosimeter by convoluting the sensitivity spectrum to the solar UV spectra. We found that 305-310 nm is the maximum for both the solar erythema effectiveness and polysulphone sensitivity to solar UV radiation. Polysulphone measurements made during a 7 year peroid were collected and fitted to model solar UVB. A shift was found between measured data and the calculated results. We propose that this shift may be attributed to the seasonal variation at the stratospheric ozone layer.