The dependence of radiation transmission on sample thickness was studied in isolated samples of human stratum corneum and full‐thickness epidermis. The investigation also included samples of skin repeatedly exposed to UV‐B. Transmission was measured in the ultraviolet and in the visible from 248–546 nm. Two methods, one microscopic and the other mechanical, were used to measure thickness. There was a good correlation between the results. The dependence of transmission on thickness in these samples could be described satisfactorily by an exponential function, implying that the Lambert‐Beer law is approximately valid. Thus, a single parameter, such as the half‐value layer (d½), is sufficient to characterize absorption in the skin samples. Water content of the isolated stratum corneum was influenced by maintenance conditions: samples floating on water containing a small amount of NaCl were more hydrated than samples floating on a more concentrated salt solution, or stored in air. Changes in water content of the samples resulted in changes of thickness and, to a lesser extent, of transmission. Approximate in vivo values of d½ were computed after estimating the in vivo water content of stratum corneum. Differences found in the shape of the transmission spectra of stratum corneum and full‐thickness epidermis may reflect differences in chemical composition. The influence of wetting of the skin on its sensitivity to sunlight is explained in a new way.
Depletion of the ozone layer has been observed on a global scale, and is probably related to halocarbon emissions. Ozone depletion increases the biologically harmful solar ultraviolet radiation reaching the surface of the Earth, which leads to a variety of adverse effects, including an increase in the incidence of skin cancer. The 1985 Vienna Convention provided the framework for international restrictions on the production of ozone-depleting substances. The consequences of such restrictions have not yet been assessed in terms of effects avoided. Here we present a new method of estimating future excess skin cancer risks which is used to compare effects of a 'no restrictions' scenario with two restrictive scenarios specified under the Vienna Convention: the Montreal Protocol, and the much stricter Copenhagen Amendments. The no-restrictions and Montreal Protocol scenarios produce a runaway increase in skin cancer incidence, up to a quadrupling and doubling, respectively, by the year 2100. The Copenhagen Amendments scenario leads to an ozone minimum around the year 2000, and a peak relative increase in incidence of skin cancer of almost 10% occurring 60 years later. These results demonstrate the importance of the international measures agreed upon under the Vienna Convention.
[1] The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA EOS Aura spacecraft is a nadir viewing spectrometer that measures solar reflected and backscattered light in a selected range of the ultraviolet and visible spectrum. The instrument has a 2600 km wide viewing swath and it is capable of daily, global contiguous mapping. The Finnish Meteorological Institute and NASA Goddard Space Flight Center have developed a surface ultraviolet irradiance algorithm for OMI that produces noontime surface spectral UV irradiance estimates at four wavelengths, noontime erythemal dose rate (UV index), and the erythemal daily dose. The overpass erythemal daily doses derived from OMI data were compared with the daily doses calculated from the ground-based spectral UV measurements from 18 reference instruments. Two alternative methods for the OMI UV algorithm cloud correction were compared: the plane-parallel cloud model method and the method based on Lambertian equivalent reflectivity. The validation results for the two methods showed some differences, but the results do not imply that one method is categorically superior to the other. For flat, snow-free regions with modest loadings of absorbing aerosols or trace gases, the OMI-derived daily erythemal doses have a median overestimation of 0-10%, and some 60 to 80% of the doses are within ±20% from the ground reference. For sites significantly affected by absorbing aerosols or trace gases one expects, and observes, bigger positive bias up to 50%. For high-latitude sites the satellite-derived doses are occasionally up to 50% too small because of unrealistically small climatological surface albedo.
Spectrally resolved UV measurements are important for the study of biologically relevant UV in relation to changes in atmospheric parameters. The inter‐comparison of spectral instruments is essential as measurement techniques and calibrations are not standardized. The differences in slit functions cause large spectral variations when comparing the spectral readings directly. The method described, which compares spectral readings using different instruments, corrects for differences of wavelength calibrations and slit functions, and does not require knowledge of additional atmospheric parameters and UV‐transfer model calculations. The wavelength alignment has an accuracy of 0.02 nm over the wavelength interval from 300–400 nm, and a reproducibility of 0.01 nm. The robustness of the methods and reproducibility of results are shown in the evaluation of a seven day intercomparison campaign with three different scanning spectroradiometers.
[1] The variability and long-term changes in the ultraviolet (UV) climate in the Netherlands have been studied in relation to ozone and clouds, by analyzing modeled and measured values for daily, monthly, and yearly integrated erythemally weighted UV doses. At Bilthoven, Netherlands (longitude 5.19°E, latitude 52.12°N), UV irradiance measurements for the 1994-2003 period yielded a mean annual dose of 447 ± 29 kJ/m 2 and a mean daily dose of 2.5 ± 0.5 kJ/m 2 for June and July. On average, the maximum UV index exceeded 6.5 (i.e., 0.1625 W/m 2 erythemally weighted) on 10 days per year (21 days in 2003). The mean value of measured-to-modeled ratios of erythemal UV irradiances was 1.00 with a standard deviation of 0.06 for days when the measured global solar radiation agrees within 5% with the cloudless sky value. Three previously introduced approaches to model cloud effects on UV doses were shown to have limitations when applied for low Sun and/or optically thick clouds, while a new approach provided the most consistent results with an average ratio of the measured-to-modeled daily doses of 1.02 and a standard deviation of 0.09, for all seasons and weather conditions for the period 1994-2002. Further analysis also revealed a wavelength dependency of the correlation between global solar radiation and UV radiation. Clouds, on average, reduced the daily dose of erythemal UV to 68% of the clear-sky value, whereas for global solar radiation this was 57%. The modeled annual erythemal UV dose was 622 kJ/m
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