UV Index experimental values on vertical surfaces

Transcription

1 INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 32: (2012) Published online 31 August 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: /joc.2423 UV Index experimental values on vertical surfaces M. P. Utrillas, a J. A. Martínez-Lozano, a *A.R.Esteve, a D. Serrano a and M. J. Marín b a Departament de Física de la Terra i Termodinàmica, Universitat de Valencia, Dr. Moliner 50, Burjassot, Valencia, Spain b Departament de Matemàtiques per a l Economia i l Empresa, Universitat de València, Avda. Tarongers s/n, Valencia, Spain ABSTRACT: UV erythemal irradiance (UVER) has been studied on a horizontal plane and on vertical surfaces with different orientations in Valencia, Spain. The evolution of the solar noon value and the maximum daily value over a year has been analysed from the instantaneous UVER taken every five minutes on the horizontal plane and on vertical surfaces with north, south, east and west orientations. The annual evolution of these values shows a sinusoidal form for all planes except for the vertical south plane with maxima in spring and autumn. The UV Index (UVI) on these planes was also determined. The percentage of coincidence of the UVI at solar noon and of the maximum daily UVER values, considering differences of 1 or 0 units, is 87% on the horizontal plane, 100% on the vertical north plane, 92% on the vertical south plane, 77% on the vertical east plane and 75% on the vertical west plane. We have compared the UVI of the vertical plane with the horizontal one by means of linear regressions. All planes show very good correlations except for the vertical south plane, which shows no correlation with the horizontal plane for the middle days of the year due to its particular geometry with respect to the Sun s apparent path. Finally, the annual cumulative UVER doses related to each phototype for the horizontal and vertical planes were calculated. It was noticed that the dose over a year on the horizontal plane doubles the dose on the vertical south plane, which is the one that receives the maximum dose. Copyright 2011 Royal Meteorological Society KEY WORDS vertical surface; UV erythemal radiation (UVER); UV Index (UVI) Received 27 December 2010; Revised 27 July 2011; Accepted 31 July Introduction The effects of UV radiation on human beings have received considerable attention over the past 30 years (Frederick and Lubin, 1988; Scotto et al., 1988), leading to guidelines and recommendations about UV radiation exposure in order to avoid specific or chronic damage to the skin (WMO, 1998; ICNIRP, 2004). The most common effect of UV radiation on humans is erythema or sunburn. The Comission Internationale de l Éclairage (CIE) adopted a standard erythema curve in 1987 (McKinlay and Diffey, 1987; CIE, 1999) which is currently recommended for determining the UV erythemal radiation (UVER). The erythemal action spectrum has been defined by humans to describe the dependence of skin reaction on the spectral irradiance. The UVER is calculated by weighting the spectral curve of the incident solar radiation at ground level with the spectral action curve proposed by the CIE. The study of the erythemal influence has been frequently based on the minimum dose of UVER that produces a noticeable reddening of human skin not exposed previously to solar radiation. This dose is known internationally as MED (Minimum Erythemal Dose) (Diffey, 1990; Grainger et al., 1993), and is always related to a * Correspondence to: J. A. Martínez-Lozano, Solar Radiation Group, University of Valencia, Dr. Moliner 50, Burjassot (Valencia), Spain. jmartine@uv.es specific skin type (phototype). The principal characteristics of these phototypes and the dose (expressed in J/m 2 ) needed to produce one MED are shown in Table I (Vanicek et al., 2000; DIN 5050, 1992). The CIE also defined a Standard Erythemal Dose (SED) that corresponds to 100 J/m 2 (weighted at 297 nm), which does not depend on the skin type and should be used instead of MED (CIE, 2000). The UV Index (UVI) is the parameter used to inform and increase public awareness on exposure levels to UVER and its possible health risks. The UVI is determined from the integrated UVER (expressed in W/m 2 ) multiplied by 40. It is expressed as a whole number (the nearest integer) and is always defined on a horizontal surface. Depending on the phototype, it is usual to consider high erythema risk for values greater than six and extreme risk for values above nine. The measurement of the UVER on a horizontal surface is not always the most suitable method to estimate the real dosage received by human beings. For this reason, knowing the irradiance incident on tilted surfaces can be important for dosimetric studies. Webb et al. (1999) performed a study of spectral UV measurements on vertical planes and various azimuth angles, and their data was used to validate the results of some simulations using a radiative transfer model (Mech and Koepke, 2004). Moreover, Parisi and Kimlin (1999) showed that the global UVER on a plane normal to the Sun can Copyright 2011 Royal Meteorological Society

2 UV INDEX EXPERIMENTAL VALUES ON VERTICAL SURFACES 2067 Table I. Definition of basic phototypes (COST-713) for the European population and their Minimum Erythemal Doses values (MED). Skin types Tanning ability Typical features MED Type I Type II Type III Type IV never tans, always burns sometimes tans, sometimes burns always tans, rarely burns always tans, never burns red hair, blue eyes blond hair, blue/green eyes brown hair, gray/brown eyes black hair, brown eyes 200 J/m J/m J/m J/m 2 Figure 1. Experimental setup for measuring UV erythemal irradiance on vertical planes (partial view). This figure is available in colour online at wileyonlinelibrary.com/journal/joc reach up to 27% above that incident on a horizontal plane, while the diffuse UVB and UVER irradiances are less for a plane normal to the Sun compared with a horizontal orientation. The influence of the topography and soil reflectivity have been studied by Weihs (2002), deducing that the UVER on tilted planes increases considerably with altitude. An angle scanning radiometer for determination of the UV erythemal irradiance on tilted surfaces has been developed by Oppenrieder et al. (2004). Esteve et al. (2006), Utrillas et al. (2009), and Serrano et al. (2010) published the first results of UVI values on tilted planes. These values were measured on tilted planes with an inclination of 40 over the horizontal plane, an angle close to the latitude of the location of the study (Valencia, Spain). Recently, the Solar Radiation Group of Valencia has launched a station for measuring UVER on vertical planes at the Faculty of Physics of the University of Valencia (Derouet et al., 2011). In this work, the experimental data obtained at this station have been used to calculate the UVI on vertical planes with north, south, east, and west orientations. 2. Materials and methods A field station was designed and deployed for measuring UVER on vertical surfaces. The measurement station is located on the roof of the Faculty of Physics in Burjassot, Valencia, Spain. The roof surface is made of concrete, with an albedo of 0.10 in the UV spectral range and 0.20 in the broadband. The obstructions above the horizon are less than 4, except in a small zone in the northwest. The UVER station consists of six broadband UVB-1 radiometers by YES (Yankee Environmental Systems). One radiometer measures the total irradiance on the horizontal plane. The second instrument has a shadow band that blocks direct sunlight from falling on the detector, therefore, diffuse irradiance on a horizontal plane is measured (Utrillas et al., 2007). The other four radiometers measure total irradiance on vertical planes with north, south, east, and west orientations (Figure 1). The YES UVB-1 radiometer has a spectral range between 280 and 400 nm, and a spectral sensitivity close to the erythemal action spectrum. It is designed to be stable over long time periods and to operate continuously and autonomously in the field. The cosine response is less than 4% for solar zenith angles below 55 (Dichter et al., 1993), according to the manufacturer. The YES UVB-1 used to measure the total irradiance on the horizontal plane is calibrated in the National Institute for Aerospace Technology in Spain. This standard calibration consists of a measurement of the spectral response of the radiometer indoors and a comparison with a Brewer MKIII spectroradiometer outdoors (Vilaplana et al., 2006; Hülsen and Gröbner, 2007). It is necessary to choose a cutoff criterion in order to ensure that the data is not affected by an excessively high error. For a constant ozone value of 300 Dobson units, the error given by the calibration matrix is below 9% for zenith angles below 70, reaching 16% for zenith angles of 75. In order to use a general criterion, easy to reproduce to other similar radiometers, 70 was taken as a cutoff point, thus ensuring an error of less than 10% in the experimental values (Utrillas et al., 2007). The YES UVB-1, used to measure the total irradiance on vertical planes and the diffuse UVER with the shadow band, have been calibrated by intercomparison with the total irradiance instrument. The measurements of UVER presented in this study correspond to a complete year (from 1 June 2009 to 31 May 2010), and they are representative of Valencia since the atmospheric conditions (cloudiness, ozone, aerosol optical depth, etc.) for this year were completely normal. As an example, the cloudiness and the aerosol optical depth (AOD) for this year have been compared with longer time periods. Figure 2 represents the recurrence of days with specific cloud conditions for a period of 11 years ( ) and the considered year (2009/2010), grouping the days according to the cloud amounts, measured in oktas (0 2 oktas, 3 5

3 2068 M. P. UTRILLAS et al. Thus, these atmospheric effects, which have a minimal influence in the determination of the UVI, have not been taken into account. Measurements were taken continuously and instantaneous values were registered every five minutes in irradiance units (W/m 2 ). The daily values of the UVI were determined using two different criteria: (1) the solar noon value; (2) the maximum daily value, following the recommendations of WHO/WMO/ICNIRP/UNEP (ICNIRP, 1995; WMO, 1998) and COST 713 Action (Vanicek et al., 2000). Figure 2. Recurrence of days (in %) with specific cloud conditions for a period of 11 years ( ) and the considered year (2009/2010), grouping the days according to the cloud amounts, measured in oktas (0 2 oktas, 3 5 oktas, 6 7 oktas and 8 oktas). AOD 500 nm Estellés et al. (2007) Month Figure 3. Annual evolution of the aerosol optical depth (AOD) at 500 nm measured by AERONET in Burjassot for the period , as well as the monthly values of the climatology made by Estellés et al. (2007) for the same location. oktas, 6 7 oktas and 8 oktas). There is a good coincidence between the two periods, and thus the analysed year can be considered representative of a longer time period. Figure 3 shows the annual evolution of the AOD at 500 nm measured by AERONET in Burjassot for the period of , as well as the monthly values of the climatology made by Estellés et al. (2007) for the same location. Although the difference between periods is greater than in the case of cloudiness, there is fair agreement between them. Therefore, we can consider the radiation measurements presented in this study representative of the atmospheric conditions for Valencia. The aerosol optical depth and the atmospheric moisture are indeed two parameters of great importance for the UVB radiation (nearly as important as the stratospheric ozone), and the authors have analysed them in previous papers (e.g. Esteve et al., 2009, 2010; Martínez-Lozano et al., 2011). However, since the focus of this work is to present long-term measurements of the UVI on vertical planes, and it uses UVER values over vertical and horizontal planes measured simultaneously, we have considered that these effects are the same over both planes, not affecting the final relationship between the radiation for the fixed planes with different inclinations. 3. Results and discussion 3.1. Annual evolution of the UVER Figures 4 and 5 show the annual evolution of the daily values of UV erythemal irradiance (UVER) at solar noon for a horizontal plane and four vertical planes with north, south, east and west orientations, respectively. The maximum daily UVER values are also shown in Figures 4 and 5. For an easier analysis, a standard year has been created representing successively the 1 January to 31 May 2010, and the 1 June to 31 December 2009 periods. The envelope of the curves for the horizontal plane and vertical north, east and west planes has a sinusoidal form, and it represents the UVER on cloudless days. The envelope of the curve for the vertical south plane shows two different maxima in spring and autumn. Moreover, while curves representing the solar noon and maximum daily UVER values for the horizontal and the vertical north and south planes match perfectly, the curves for the vertical east and west planes show a substantial difference, especially in the middle days of the year. In these cases, the maximum daily values are reached not at solar noon, but in the morning (east plane) and in the afternoon (west plane). The minimum UVER value is 0.01 W/m 2 for all planes, and the maximum value is 0.25 W/m 2 for the horizontal plane, 0.05 W/m 2 for the vertical north plane and 0.10 W/m 2 for the vertical south, east and west planes. The maximum UVER value UVER (Wm 2 ) Day UVER-HZ-MX UVER-HZ Figure 4. Annual evolution of the UVER daily values at solar noon and the maximum daily values on a horizontal plane.

4 UV INDEX EXPERIMENTAL VALUES ON VERTICAL SURFACES 2069 Figure 5. Annual evolution of the UVER daily values at solar noon and the maximum daily values on a vertical plane facing (a) north, (b) south, (c) east and (d) west. on the horizontal plane agrees with the value previously obtained by Martínez-Lozano et al. (2002b) and Marín et al. (2005) Experimental maximum daily and solar noon daily UVI The UVI at solar noon has been compared with the maximum daily UVI for the horizontal plane and the vertical planes with north, south, east and west orientations. We carried out an elementary statistical analysis to establish the differences between the results. For each plane, the percentages were found for which the differences in the results given by the two criteria were 0, 1, 2 and 3 or more units of UVI. The results of this analysis are summarized in Table II. On the horizontal plane and the vertical north and south planes there is a high percentage of coincidence. We emphasize that, independently of the criterion used, differences of just W/m 2 in the UVER values can lead to differences of 1 unit in the UVI due to the rounding needed to express the UVI as a whole number. Thus, the percentage of coincidence is 87% for the horizontal plane, 100% for the vertical north plane and 92% for the vertical south plane, considering the cases for which the difference between the UVI at solar noon and the maximum daily value is 0 or 1. Therefore, on these planes it is reasonable to consider the maximum daily UVI as the value corresponding to the solar noon, which is much easier to determine. This criterion has been followed by the authors on some previous works (Martinez-Lozano et al., 2002a, 2002b; Marín et al., 2005). However, this criterion cannot be Table II. Percentages of cases in which the difference between the UVI at solar noon and the maximum daily UVI are 0, 1, 2 or 3 units for the horizontal and vertical planes. Difference Horizontal North South East West used to determine the UVI on the vertical east and west planes due to their particular geometry with respect to the Sun s apparent path, as the percentage of coincidence between the UVI at solar noon and the maximum daily values falls to 77 and 75%, respectively. The maximum daily values for every month and plane are shown in Table III. Although the UVI on the horizontal plane reaches a value of 10 in June and July, none of the vertical planes reaches a value greater than 4, finding the lowest value for June or July (UVI = 2) on the vertical north plane. These results are completely analogous to the ones obtained by Oppenrieder et al. (2004) for one clear sky day of summer, 4 July 2002, and winter, 15 December 2001, at a measuring site in München (Germany) Comparison between the vertical and horizontal UVI After analysing the UVI on vertical planes with different orientations, it would be interesting to compare these

5 2070 M. P. UTRILLAS et al. Table III. Monthly maximum values of the UVI for the horizontal and vertical planes. Month Horizontal North South East West January February March April May June July August September October November December MEDS Horizontal Phototype I Phototype II Phototype III Phototype IV Day Figure 7. Irradiation on a horizontal plane, accumulated over the year, expressed in MED, for different skin photo types. UVI 5.0 UVI-N-MX UVI-S-MX 4.5 y = 0.20x UVI-E-MX r 2 = 0.79 UVI-W-MX 4.0 Lineal (UVI-N-MX) y = 0.46x Lineal (UVI-S-MX) r 2 = Lineal (UVI-E-MX) Lineal (UVI-W-MX) y = 0.42x r 2 = y = 0.42x 2.5 r 2 = UVI-HZ Figure 6. Linear regressions of the UVI on vertical planes with north, south, east, and west orientations against the UVI on a horizontal plane. values with the UVI values obtained on a horizontal plane. In order to do this, we have represented the UVI for each vertical plane (north, south, east and west) against the UVI for the horizontal plane over the year considered in this study (Figure 6). Although the UVI is defined as a whole number, in this case we have used the value obtained by multiplying the UVER by 40 and not rounding off the result. Very good correlations are observed for all vertical planes, except for the vertical south plane, which due to its particular geometry with respect to the Sun s apparent path does not show any correlation with the horizontal plane in the middle days of the year. The linear regressions, which allow us to estimate the UVI on vertical planes with north, east and west orientations, according to the UVI experimental values on the horizontal plane are: North plane: UVI N = 0.20 UVI H (r = 0.79) (1) East plane: UVI E = 0.42 UVI H (r = 0.96) (2) West plane: UVI W = 0.42 UVI H (r = 0.94) (3) 3.4. Annual cumulative doses From the instantaneous UVER values taken every five minutes, hourly and daily UVER values were calculated. The daily UVER data was used to calculate the annual cumulative doses related to each phototype for the horizontal and vertical planes (Figures 7 and 8). It is worth pointing out that these values represent the dose accumulated in an uninterrupted exposure to the Sun in this position over all the hours of all the days of the year. The curves in these figures clearly show the increase of slope corresponding to the summer months. In these exposure conditions, it can be seen that, for example, a Type I skin would receive on a horizontal plane approximately 4000 MEDs during the year, more than half of which correspond to the summer months. Figure 9 shows the comparison of the SED for each different plane. The accumulated UVER dose in the south vertical plane is greater than the accumulated UVER dose in the north, east and west vertical planes. Moreover, the dose over a year on the horizontal plane doubles the dose of the vertical plane, namely the vertical south plane, which receives the maximum dose. 4. Conclusions UV erythemal irradiance has been studied on a horizontal plane and on vertical surfaces with different orientations in Valencia, Spain. From the instantaneous UVER values taken every five minutes over a year on the horizontal plane and vertical surfaces with north, south, east, and west orientations, the UVER value at solar noon and the UVER maximum daily value have been determined. The annual evolution of these values shows a sinusoidal form for all planes except for the vertical south plane, which presents two different maxima in spring and autumn. The minimum UVER value is 0.01 W/m 2 for all planes, and the maximum value is 0.25 W/m 2 for the horizontal plane, 0.05 W/m 2 for the vertical north plane and 0.10 W/m 2 for the vertical south, east and west planes.

6 UV INDEX EXPERIMENTAL VALUES ON VERTICAL SURFACES 2071 Figure 8. Irradiation on a vertical plane facing (a) north, (b) south, (c) east and (d) west, accumulated over the year, expressed in MED, for different skin photo types. SED Hz 90 N 90 S 90 E 90 W Day Figure 9. Irradiation accumulated over the year, expressed in SED for different planes. The UVI at solar noon has been compared with the maximum daily UVI for the horizontal plane and the vertical planes with north, south, east and west orientations. Considering the cases for which the difference between the two UVI values is 0 or 1, the percentage of coincidence is 87% for the horizontal plane, 100% for the vertical north plane and 92% for the vertical south plane. Therefore, it is reasonable to consider the maximum daily UVI value for these planes as the value corresponding to the solar noon. However, this criterion cannot be used to determine the UVI on the vertical east and west planes, as their geometry with respect to the Sun s apparent path leads to a lower percentage of coincidence (77 and 75%, respectively). The UVI for the north, south, east, and west vertical planes has been compared with the UVI of the horizontal plane by means of linear regressions. All planes show very good correlations (r >0.78), except the vertical south plane, which due to its geometry with respect to the Sun s apparent path shows no correlation with the horizontal plane for the middle days of the year. Finally, the annual cumulative UVER doses related to each phototype for the horizontal and vertical planes were calculated, obtaining that the dose within a year on the horizontal plane doubles the one on the vertical plane that receives the maximum dose, the vertical south plane in this case. Acknowledgements This work was funded by the Ministry of Science and Innovation (MICINN) of the Spanish Government through the Projects CGL , CGL and CGL , and by the Valencia Autonomous Government through the Project PROMETEO/2010/064. References CIE (Commission Internationale de l Éclairage) Standardization of the terms UV-A1, UV-A2 and UV-B. Vienna, CIE; Report CIE- 134/1. CIE (Commission Internationale de l Éclairage) ISO CIE S 007/E. Erythema Reference Action Spectrum and Standard Erythema Dose, CIE Standard, 4 pp. CIE, Publications, Vienna. Derouet G, Utrillas MP, Estellés V, Esteve AR, Marín MJ, Gómez- Amo JL, Martínez-Lozano JA Estimación de la irradiancia UV eritematica integrada incidente en planos verticales, mediante el modelo SMARTS2. TETHYS 8:

7 2072 M. P. UTRILLAS et al. Dichter BK, Beaubien AF, Beaubien DJ Development and characterization of a new solar ultraviolet-b irradiance detector. Journal of Atmospheric and Oceanic Technology 10: Diffey BL Human Exposure to Ultraviolet Radiation. Seminars in Dermatology 9: DIN Solarien und Heimsonnen: Meßverfahren, Typeneinteilung und Kennzeichnung (Solariums and domestic sun lamps: Measuring, marking and classification), Part I. Beuth, 8. Estelles V, Martinez-Lozano JA, Utrillas MP, Campanelli M Columnar aerosol properties in Valencia (Spain) by groundbased Sun photometry. Journal Geophysical Research 112: DOI: /2006JD Esteve A, Martínez-Lozano JA, Marin MJ, Estellés V, Tena F, Utrillas MP Influence of the ozone and the aerosols over experimental values of UVER a ground level, at Valencia. International Journal of Climatology 29: DOI: / joc Esteve A, Marín MJ, Tena F, Utrillas MP, Martínez-Lozano JA The influence of cloudiness over the values of UVER in Valencia, Spain. International Journal of Climatology 30: DOI: /joc Esteve AR, Marín MJ, Martínez-Lozano JA, Tena F, Utrillas MP, Cañada J UV Index on tilted surfaces. Photochemistry and Photobiology 82: DOI: / RA-743. Frederick JE, Lubin D The budget of biologically active radiation in the earth atmosphere system. Journal of Geophysical Research 93: Grainger RG, Basher RE, McKenzie RL UV-B Robertson- Berger meter characterization and field calibration. Applied Optics 32: Hülsen G, Gröbner J Characterization and calibration of ultraviolet broadband radiometers measuring erythemally weighted irradiance. Applied Optics 46(23): ICNIRP (International Commission on Non-Ionizing Radiation Protection) Global Solar UV Index, WHO/WMO/INCIRP recommendation, INCIRP publication no 1/95, Oberschleissheim. ICNIRP (International Commission on Non-Ionizing Radiation Protection) Guidelines on limits of exposure of UV radiation. Health Physics 87: Marín MJ, Sola Y, Tena F, Utrillas MP, Campmany E, de Cabo X, Lorente J, Martínez-Lozano JA The UV Index on the Spanish Mediterranean coast. Photochemistry and Photobiology 81: Martínez-Lozano JA, Marín MJ, Tena F, Utrillas MP, Sánchez- Muniosguren L, González C, Cuevas E, Redondas A, Lorente J, de Cabo X, Cachorro V, Vergaz R, de Frutos A, Díaz JP, Expósito FJ, de la Morena B, Vilaplana JM. 2002a. UV Index experimental values during the years 2000 and 2001 from the Spanish broadband UVB radiometric network. Photochemistry and Photobiology 76: Martínez-Lozano JA, Tena F, Marín MJ, Utrillas MP, Lorente J, de Cabo X, González C. 2002b. Experimental values of the UV Index during 2000 at two locations in Mediterranean Spain. International Journal of Climatology 22: Martínez-Lozano JA, Utrillas MP, Núñez JA, Tamayo J, Cañada J, Moreno JC, Marín MJ, Esteve AR Ozone mini-holes over Valencia, Spain. Its influence on the erythematic UVB radiation (UVER). International Journal of Climatology 31: McKinlay AF, Diffey BL A reference spectrum for ultraviolet induced erythema in human skin. CIE Journal 6: Mech M, Koepke P Model for UV irradiance on arbitrarily oriented surfaces. Theoretical and Applied Climatology 77: Oppenrieder A, Hoeppe P, Koepke P Routine measurement of erythemally effective UV irradiance on inclined surfaces. Journal of Photochemistry and Photobiology B: Biology 74: Parisi AV, Kimlin MG Horizontal and sun-normal spectral biologically effective ultraviolet irradiances. Journal of Photochemistry and Photobiology B: Biology 53: Scotto J, Cotton G, Urbach F, Berger D, Fears T Biologically effective ultraviolet radiation: surface measurements in the United States, 1974 to Science 239: Serrano D, Marín MJ, Utrillas MP, Tena F, Martínez-Lozano JA Medida y modelización de la irradiancia solar eritemática global sobre planos inclinados. TETHYS 7: Utrillas MP, Marín MJ, Esteve AR, Tena F, Cañada J, Martínez-Lozano JA Diffuse UVER radiation experimental values. Journal of Geophysical Research 112: D DOI: /2007JD Utrillas MP, Marín MJ, Esteve AR, Estelles V, Tena F, Cañada J, Martínez-Lozano JA Diffuse ultraviolet erythematic irradiance (UVER) on inclined planes: a comparison of experimental and modelled data. Photochemistry and Photobiology 85: DOI: /j x. Vanicek K, Frei T, Litynska Z, Schnalwieser A lamma.rete.toscana.it/uvweb/index.html UV-Index for the public, COST-713 Action (UV-B Forecasting), Brussels, 27. Vilaplana JM, Cachorro VE, Sorribas M, Luccini E, de Frutos AM, Berjón A, de la Morena B Modified calibration procedures for a yankee environmental system UVB-1 biometer based on spectral measurements with a brewer spectrophotometer. Photochemistry and Photobiology 82: Webb A, Weihs P, Blumthaler M Spectral UV Irradiance on Vertical Surfaces: A Case Study. Photochemistry and Photobiology 69: Weihs P Influence of ground reflectivity and topography on erythemal UV radiation on inclined planes. International Journal of Biometeorology 46: WMO (World Meteorological Organization) Report of the WMO WHO Meeting of Experts on Standardization of UV Indices and Their Dissemination to the Public. WMO Global Atmosphere Watch No. 127, WMO/TD No. 921, Geneva.