All-Weather Comparison between Spectral and Broadband (Robertson-Berger) UV Measurements

Long-term ultraviolet flux, other potential risk factors, and skin cancer risk: a cohort study

BACKGROUND

Few prospective studies have examined the relationship between sun exposure, other potential risk factors, and risk of different skin cancers [including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma] simultaneously.

METHODS

We evaluated the association between a number of potential risk factors and skin cancer risk in a cohort of 108,916 US women, the Nurses' Health Study II (1989-2009).

RESULTS

During 2.05 million years of follow-up, we identified 6,955, 880, and 779 diagnoses of BCC, SCC, and melanoma, respectively. Compared with participants in the lowest quintile of cumulative ultraviolet flux in adulthood, participants in the highest quintile had multivariable-adjusted relative risks (RR) of 2.35 (Ptrend < 0.0001) for BCC, 2.53 (Ptrend = 0.009) for SCC, and 0.68 (Ptrend = 0.38) for melanoma. In contrast, the RRs were 1.68 (95% CI, 1.55-1.82) for BCC, 1.68 (95% CI, 1.34-2.11) for SCC, and 1.80 (95% CI, 1.42-2.28) for melanoma for participants with ≥5 blistering sunburns when compared with participants without sunburn between ages 15 and 20 years. We found significant interactions between family history of melanoma, number of blistering sunburns between ages 15 and 20 years and BCC risk, and between sunburn reaction as a child/adolescent and SCC risk (all Pinteraction < 0.05).

CONCLUSION

In a cohort of U.S. women, we found that sun exposures in both early life and adulthood were predictive of BCC and SCC risks, whereas melanoma risk was predominantly associated with sun exposure in early life.

IMPACT

Our results may have potential implications for the prevention of skin cancers. Cancer Epidemiol Biomarkers Prev; 23(6); 1080-9. ©2014 AACR.

UV index experimental values during the years 2000 and 2001 from the Spanish broadband UV-B radiometric network

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.

Influence of spectral and angular sensitivity on the readout of biological dosimeters

Biological systems used as biological dosimeters can possess different angular sensitivities from the detectors usually used in physical devices. A simple experimental setup has been developed and used to measure the angular sensitivity of uracil thin-layer biological dosimeters. Results of angular sensitivity measurements for uracil thin-layer dosimeters are presented using a Xe arc lamp as the UV source. According to the experiments described here, uracil thin-layer dosimeters show a cosine-type angular dependence. In several indoor experiments broadband UV meters are used to control the applied dose rate from a given artificial UV source. The experimental setup has been designed and used to verify experimentally the importance of spectral and angular sensitivity differences of biological and physical UV meters applied in biological experiments. Model calculations for two different irradiation systems, using different geometrical arrangements of artificial UV sources, are also presented. For these arrangements relative dose rates that could be measured with dosimeters of arbitrary spectral, but different angular sensitivity have been calculated.

Changes in biologically active ultraviolet radiation reaching the Earth's surface

Stratospheric ozone levels are near their lowest point since measurements began, so current ultraviolet-B (UV-B) radiation levels are thought to be close to their maximum. Total stratospheric content of ozone-depleting substances is expected to reach a maximum before the year 2000. All other things being equal, the current ozone losses and related UV-B increases should be close to their maximum. Increases in surface erythemal (sunburning) UV radiation relative to the values in the 1970s are estimated to be: about 7% at Northern Hemisphere mid-latitudes in winter/spring; about 4% at Northern Hemisphere mid-latitudes in summer/fall; about 6% at Southern Hemisphere mid-latitudes on a year-round basis; about 130% in the Antarctic in spring; and about 22% in the Arctic in spring. Reductions in atmospheric ozone are expected to result in higher amounts of UV-B radiation reaching the Earth's surface. The expected correlation between increases in surface UV-B radiation and decreases in overhead ozone has been further demonstrated and quantified by ground-based instruments under a wide range of conditions. Improved measurements of UV-B radiation are now providing better geographical and temporal coverage. Surface UV-B radiation levels are highly variable because of cloud cover, and also because of local effects including pollutants and surface reflections. These factors usually decrease atmospheric transmission and therefore the surface irradiances at UV-B as well as other wavelengths. Occasional cloud-induced increases have also been reported. With a few exceptions, the direct detection of UV-B trends at low- and mid-latitudes remains problematic due to this high natural variability, the relatively small ozone changes, and the practical difficulties of maintaining long-term stability in networks of UV-measuring instruments. Few reliable UV-B radiation measurements are available from pre-ozone-depletion days. Satellite-based observations of atmospheric ozone and clouds are being used, together with models of atmospheric transmission, to provide global coverage and long-term estimates of surface UV-B radiation. Estimates of long-term (1979-1992) trends in zonally averaged UV irradiances that include cloud effects are nearly identical to those for clear-sky estimates, providing evidence that clouds have not influenced the UV-B trends. However, the limitations of satellite-derived UV estimates should be recognized. To assess uncertainties inherent in this approach, additional validations involving comparisons with ground-based observations are required. Direct comparisons of ground-based UV-B radiation measurements between a few mid-latitude sites in the Northern and Southern Hemispheres have shown larger differences than those estimated using satellite data. Ground-based measurements show that summertime erythemal UV irradiances in the Southern Hemisphere exceed those at comparable latitudes of the Northern Hemisphere by up to 40%, whereas corresponding satellite-based estimates yield only 10-15% differences. Atmospheric pollution may be a factor in this discrepancy between ground-based measurements and satellite-derived estimates. UV-B measurements at more sites are required to determine whether the larger observed differences are globally representative. High levels of UV-B radiation continue to be observed in Antarctica during the recurrent spring-time ozone hole. For example, during ozone-hole episodes, measured biologically damaging radiation at Palmer Station, Antarctica (64 degrees S) has been found to approach and occasionally even exceed maximum summer values at San Diego, CA, USA (32 degrees N). Long-term predictions of future UV-B levels are difficult and uncertain. Nevertheless, current best estimates suggest that a slow recovery to pre-ozone depletion levels may be expected during the next half-century. (ABSTRACT TRUNCATED)

Erythemal UV irradiances at Lauder, New Zealand: relationship between horizontal and normal incidence

Measurements from sensors designed to measure erythemal UV irradiance were used to relate the UV incident on a horizontal surface to that incident on a surface maintained normal to the sun throughout the day at Lauder, New Zealand. These UV measurements were also related to variations in global radiation, total column ozone and atmospheric pressure at the surface. Strong correlations were found between these variables over the 37 day observation period in the summer of 1995/1996. Results from these cross-calibrated UV sensors show that the irradiance incident on a surface normal to the sun can be significantly different from that on a horizontal surface. On clear days, the normal-incidence signal can be 30-40% greater for solar zenith angles in the range 60-70 degrees. Consequently, the risk of UV damage can be greater than reported by measurements or models that assume horizontal incidence (e.g., UV index). On cloudy days the normal-incidence UV can be less than 50% of the horizontal-incidence UV. Averaged over a day, any enhancements in normal-incidence UV over horizontal-incidence UV are smaller. The effects were strongly dependent on cloud conditions. Under clear skies the enhancements are generally less than 10%, and the integrated excess over horizontal-incidence UV is usually less than 5%. However, under cloudy skies the reductions can still be large.