Photochemistry and Photobiology, 2005, 81: 659–665 The UV Index on the Spanish Mediterranean Coast { M. J. Marı ´n 1 , Y. Sola 2 , F. Tena 1 , M. P. Utrillas 1 , E. Campmany 2 , X. de Cabo 2 , J. Lorente 2 and J. A. Martı ´nez-Lozano* 1 1 Solar Radiation Group, University of Valencia, Valencia, Spain 2 Department of Astronomy and Meteorology, University of Barcelona, Barcelona, Spain Received 25 November 2004; accepted 10 February 2005 ABSTRACT An analysis is made of measured ultraviolet erythemal solar radiation (UVER) data recorded during the year 2003 by the networks of the Catalan Weather Service and the Environ- ment Department of Valencia (both on the Spanish Mediter- ranean coast). Results show a latitudinal variation at sea level, of 3–4% per degree and an increase with altitude of 10% per km. Based on these data the UV Index has been evaluated for the measuring stations. The maximum experimental value of the UV Index was around 9 during the summer, although higher values were recorded at two stations, one at the highest elevation and the other at the lowest latitude. The annual accumulated doses of irradiation on a horizontal plane have been presented as well as the evolution through the year in units of energy, Standard Erythemal Doses and Minimum Erythemal Doses according to different phototypes. Lastly, the UV Index forecast, determined with a multiple scattering radiative transfer model, has been analyzed. Total agreement or only one unit of difference between measured and modelled values was found in 94% of cloud-free cases. INTRODUCTION In the middle of the 1980s, spurred by public concern following the discovery of the ozone hole in the Southern Hemisphere (1), many atmospheric researchers and medical professionals recognized the need to introduce indices for predicting the doses of ultraviolet radiation incident at ground level. Such indices are aimed at raising public awareness, through the media, of the levels of UV radiation incident at ground level and the possible harmful effects of this radiation. They constitute a simple means of expressing the intensity of UV radiation in relation to its capacity to trigger certain biological processes. In 1995 the International Commission on Non-Ionizing Radia- tion Protection (ICNIRP) in collaboration with the World Health Organization (WHO), the World Meteorological Organization (WMO) and the United Nations Environmental Program (UNEP) produced recommendations redefining the UV Index (2). Sub- sequently the WMO (3) defined the amount of effective erythemal radiation as the spectral solar irradiance biologically weighted by the action spectrum recommended by the Commission Internationale de l’Eclairage (4,5) on a horizontal surface at ground level. Quan- titatively, the UV Index is determined from the integrated erythemally weighted radiation (UVER) over all wavelengths up to 400 nm (expressed in W  m 2 ) multiplied by 40. It is rounded to the nearest whole number. For sloping surfaces directed toward the sun, this value could be higher than it is on a horizontal surface (6). Forecasting of the UV Index can be done by using many different radiative transfer models, although the European Cooperation in the field of Scientific and Technical Research (COST)-713 Action of the European Commission recommends the use of multiple scattering models because these models show better agreement between simulations (7). To validate the accuracy of UV Index forecasts, it is necessary to have accurate and precise UVER measurements. Moreover, such experimental UVER values are also useful for de- veloping a UV radiation climatology and establishing geographical and seasonal distributions of UV exposure information that is useful in many areas including human health (8,9). At the beginning of 1999 the Spanish National Institute of Meteorology installed a measurement network based on broad-band radiometers. At present it consists of 16 UVB pyranometers and six Brewer spectrophotometers that are used to determine the total ozone column (10,11). At the same time, many autonomous regions, which in Spain currently have responsibility for many issues in- cluding the environment and tourism, have developed their own erythemal-radiation measurement networks. These regional net- works complement the state network with a higher spatial resolution. Two such networks are found in the regions of Catalonia and Valencia, which together occupy a large stretch of the Spanish Mediterranean coast (see Fig. 1) and receive many of the 42 million tourists that every year visit Spain, making the Catalonia–Valencia region one of the most touristic areas of Europe. This paper presents an analysis of the UV Index and correspond- ing measurements for both regions for 2003. A comparative study has been carried out between experimental and modelled values using multiple scattering radiative transfer models. This analysis {Posted on the website on 21 February 2005 *To whom correspondence should be addressed: Solar Radiation Group, University of Valencia, Dr. Moliner, 50. 46100 Burjassot (Valencia), Spain. Fax: 34-96-3543385; e-mail: jmartine@uv.es Abbreviations: DISORT, DIScreet Ordinate Radiative Transfer; ICNIRP, International Commission on Non-Ionizing Radiation Protection; MED, Minimum Erythemal Dose; RB, Robertson–Berger; SBDART, Santa Barbara DISORT Atmospheric Radiative Transfer; SED, Standard Erythemal Dose; TOMS, Total Ozone Mapping Spectrometer; UNEP, United Nations Environmental Program; UVER, ultraviolet erythemal solar radiation; WHO, World Health Organization; WMO, World Meteorological Organization. Ó 2005 American Society for Photobiology 0031-8655/05 659