Investigation of the 3-D actinic flux field in mountainous terrain.

During three field campaigns spectral actinic flux was measured from 290-500 nm under clear sky conditions in Alpine terrain and the associated O3- and NO2-photolysis frequencies were calculated and the measurement products were then compared with 1-D- and 3-D-model calculations. To do this 3-D-radiative transfer model was adapted for actinic flux calculations in mountainous terrain and the maps of the actinic flux field at the surface, calculated with the 3-D-radiative transfer model, are given. The differences between the 3-D- and 1-D-model results for selected days during the campaigns are shown, together with the ratios of the modeled actinic flux values to the measurements. In many cases the 1-D-model overestimates actinic flux by more than the measurement uncertainty of 10%. The results of using a 3-D-model generally show significantly lower values, and can underestimate the actinic flux by up to 30%. This case study attempts to quantify the impact of snow cover in combination with topography on spectral actinic flux. The impact of snow cover on the actinic flux was ~ 25% in narrow snow covered valleys, but for snow free areas there were no significant changes due snow cover in the surrounding area and it is found that the effect snow-cover at distances over 5 km from the point of interest was below 5%. Overall the 3-D-model can calculate actinic flux to the same accuracy as the 1-D-model for single points, but gives a much more realistic view of the surface actinic flux field in mountains as topography and obstruction of the horizon are taken into account.

Measuring the influence of aerosols and albedo on sky polarization.

All-sky distributions of the polarized radiance are measured using an automated fish-eye camera system with a rotating polarizer. For a large range of aerosol and surface albedo situations, the influence on the degree of polarization and sky radiance is investigated. The range of aerosol optical depth and albedo is 0.05-0.5 and 0.1-0.75, respectively. For this range of parameters, a reduction of the degree of polarization from about 0.7 to 0.4 was observed. The analysis is done for 90° scattering angle in the principal plane under clear sky conditions for a broadband channel of 450 ± 25 nm and solar zenith angles between 55° and 60°. Radiative transfer calculations considering three different aerosol mixtures are performed and and agree with the measurements within the statistical error.

Comparison of atmospheric spectral radiance measurements from five independently calibrated systems.

A variety of instruments have been developed over the past 50 years to measure spectral radiance in absolute units at UV and visible wavelengths with high spectral resolution. While there is considerable experience in the measurement of spectral irradiance, less emphasis has been given to the reliable measurement of spectral radiance from ground observations. We discuss the methodology and calibration procedures for five instruments capable of making such measurements. Four of these instruments are based on double monochromators that scan each wavelength in turn, and one is based on a single monochromator with a charged coupled device (CCD) allowing the recording of all wavelengths simultaneously. The measured spectral radiance deviates between 3% and about 35% depending on the instruments. The results are compared with radiative transfer calculations when the aerosol characteristics of the atmosphere are known.

Diurnal discrepancies in spectral solar UV radiation measurements.

Unexpected diurnal discrepancies between high-quality spectroradiometers were observed during the 2000 Nordic Ozone Group Intercomparison campaign. The spectral ratios of the irradiances showed a diurnal variation of approximately 2-9%. This cannot be explained by the nonideal angular response of the instruments' input optics in one plane (cosine effect). Instead, by using a radiative transfer model, we show that differences in the angular response in four azimuth planes have the potential to bias the measured data by up to 4.4% (azimuth effect). Other relevant factors are also discussed and quantified and are shown to be significant when diurnal changes in radiation are explained by environmental factors, or when measured data are compared with model or satellite data. Again, intercomparison campaigns have the potential to reveal errors that would otherwise remain undetected.

Spectral UV irradiance on vertical surfaces: a case study.

The UV spectral irradiance on horizontal and vertically oriented surfaces was measured throughout a cloudless day (18 July 1995) at Izana station, Tenerife, using a Bentham DTM300 spectroradiometer scanning from 290 to 500 nm in steps of 5 nm. Results show that irradiance measured on a horizontal surface is not proportional to irradiance on a vertical surface. The relation between the two depends upon orientation of the vertical surface, zenith angle and wavelength. At short UVB wavelengths surfaces directed toward the solar azimuth received their maximum irradiances much closer to solar noon than the maxima for longer wavelengths. Some vertical surfaces also received significantly more irradiance than the horizontal surface at long wavelengths during all but the central hours of the day, while at short wavelengths all vertical irradiances were less than the horizontal except for the measurements at the extreme ends of the day. Erythemally effective radiation followed the diurnal pattern of irradiations for short UVB wavelengths.

Effectiveness of eye drops protective against ultraviolet radiation.

BACKGROUND: To test the effectiveness of commercially available ultraviolet (UV)-protective eye drops (8-hydroxy-1-methylchinolinium methylsulphate) which are recommended for protection against both solar and artificial UV radiation. METHODS: The spectral transmission in the wavelength range from 250 to 500 nm was investigated in 1-nm steps using a high-resolution double monochromator with holographic gratings of 2,400 lines/mm and a 1,000-watt halogen lamp as light source. The transmission spectrum was measured for different values of the layer thickness. RESULTS: The transmission of a liquid layer of about 10 microns, which corresponds to the thickness of the human tear film, shows a cut-off at 290 nm with a transmission of about 25-50% at shorter wavelengths. For wavelengths longer than 290 nm the transmission is higher than 90%. The threshold time ratio for keratitis formation with and without eye drops is above 0.93 considering solar radiation on the earth's surface and above 0.65 considering radiation from arc-welding, respectively. DISCUSSION: The transmission spectrum of the eye drops under realistic conditions does not show a protective effect against solar UV radiation. However, there exists reduction of UVC radiation in the spectral range typical of artificial UV sources such as arc-welding. We cannot recommend the application of these eye drops as an UV-protective aid against eye damage by solar UV radiation.

Correcting global solar ultraviolet spectra recorded by a brewer spectroradiometer for its angular response error.

We present a methodology for correcting the global UV spectral measurements of a Brewer MKIII spectroradiometer for the error introduced by the deviation of the angular response of the instrument from the ideal response. This methodology is applicable also to other Brewer spectroradiometers that are currently in operation. The various stages of the methodology are described in detail, together with the uncertainties involved in each stage. Finally global spectral UV measurements with and without the application of the correction are compared with collocated measurements of another spectroradiometer and with model calculations, demonstrating the efficiency of the method. Depending on wavelength and on the aerosol loading, the cosine correction factors range from 2% to 7%. The uncertainties involved in the calculation of these correction factors were found to be relatively small, ranging from ~0.2% to ~2%.

Keratitis solaris and sunbeds.

Keratitis solaris is caused by ultraviolet radiation in the range 200-320 nm. The threshold dose for keratitis solaris is 40 J/m2 for short-term exposure. We measured the emission spectra of 22 sunbeds in the range 250-500 nm with a high-resolution double monochromator and calculated the exposure times for the threshold dose of keratitis solaris. Depending on the type of lamp used, the exposure times ranged from 90 s to 3.5 h. Lamps with short exposure times for keratitis solaris can induce keratitis solaris if protective goggles are not used (e.g., to achieve a uniform tan of the eye area) and if the eyes are opened briefly several times, perhaps, to look at a watch. Generally, sunbed users have no way of ascertaining the lamp type or its emission spectrum and of determining the exposure time for the threshold dose of keratitis solaris.

Spectral transmission of the optical media of the human eye with respect to keratitis and cataract formation.

The spectral transmissions of cornea, aqueous humour, lens and vitreous humour of human eyes were measured in the range from 250 nm to 800 nm in 1 nm steps using a high resolution double monochromator. Cornea and lens are good cut off filters; 1% transmission was measured in various cornea samples between 291 and 298 nm, and in different lenses between 389 and 414 nm. Aqueous humour and vitreous humour showed high transparency (80%) at lambda > 320 nm. The wavelength range of keratitis effective irradiance was found to be completely within the wavelength range of absorption of the cornea, that of cataract effective irradiance was found to be at the short wavelength end partly outside the wavelength range of absorption of the lens. It may therefore be supposed that the action spectrum of cataract obtained by animal experiments is applicable to the human eye only with certain reservations.

Intercomparison of spectral-UV-radiation measurement systems.

The results of what is to our knowledge the first intercomparison of seven independent spectroradiometers measuring solar UV irradiances are presented. The intercomparison was carried out in the GSF-Forschungszentrum für Umwelt und Gesundheit, Neuherberg (near Munich, Germany), on 13 July 1990. The spectroradiometric measurements were supplemented by other meteorological, optical, and chemical measurements at the same time. As this day was cloudless, the data can be compared with the measurements taken by Bener in Switzerland in the 1960's and with the results of radiative transfer models. The measured irradiances at noon differed by factors of up to 100. These large differences demonstrate the great difficulties with this type of measurement. Some instrument systems, however, ranged within tolerances of ±10%, thus allowing us to make recommendations for the spectroradiometry of solar UV irradiances.

Biological effectiveness of solar UV radiation in humans.

Solar UVB radiation is prejudicial to the health of humans in a number of ways. Erythema and photodermatoses are acute reactions of the skin; keratitis and conjunctivitis are acute reactions of the eye. Various types of skin cancer, accelerated aging of the skin, and cataract formation in the crystalline lens are reactions that appear with great latency. UV radiation can also cause damage to the immune system and DNA. For the period 1981-1991, an increase in erythemal effective UVB radiation of +(7 +/- 4)% per decade was measured in a non-polluted high mountain area (Jungfraujoch, 3576 m a.s.l., Switzerland). This increase is related to a decrease in stratospheric ozone. The effects on human health are discussed. A 10% ozone reduction increases non-melanoma skin cancer by 26% and cataract by 6 to 8%.

[Apparently supernatural healing forces from a prepared shoe]. / Vermeintlich übernatürliche Heilkräfte aus präpariertem Schuh.

Authors report on results of the examination of a specially prepared shoe, therapeutically used by a faith-healer. The patients felt unexpected sensations caused by an electrical circuit built in the shoe and released by the doctors big toe. The faith-healer justified his method to be a special kind of "electrophysiological therapy". The public prosecutor withdrew the impeachment on trickery.

[Effects of changes in total ozone on solar UV-B radiation and the biosphere]. / Auswirkungen von Anderungen des Gesamtozons auf die solare UV-B-Strahlung und die Biosphäre.

As a consequence of anthropogenic air pollution the total ozone content in the atmosphere on the northern hemisphere has slightly defined over about 20 years. This is accompanied by an increase in the biologically very effective solar UV-B-radiation. The damage of microorganisms and plants by an increase to UV-B-radiation is generally well known, but at the moment it cannot be expressed quantitatively. A consequence of increased UV-B-radiation for human beings would be an increased number of skin and eye damages. An ozone reduction by 1% would produce an increase in the 2 to 3% incidence of skin melanoma.

Indication of increasing solar ultraviolet-B radiation flux in alpine regions.

Measurements at the Jungfraujoch High Mountain Station (Swiss Alps, 47 degrees N, 3576 meters above sea level) indicate that there has been a slight increase of about 1 percent per year in the flux of solar ultraviolet-B radiation (290 to 330 nanometers) since 1981. A Robertson-Berger detector was used to measure solar erythemal radiation. The increase can be related to a long-term ozone depletion.