Ten years of measured UV Index from the Spanish UVB Radiometric Network

https://doi.org/10.1016/j.jphotobiol.2013.04.005Get rights and content

Highlights

  • Ten years of UV Index in 16 stations from the Spanish UVB Radiometric Network have been analyzed.

  • Difference between UVI at noon and maximum daily UVI was not significant.

  • Four different types of stations have been identified depending on the UVI: Coastal, Continental, Southern and Canarian.

  • Monthly average UVI at noon is recorded in July except for two stations; variability is lower in summer.

  • Cumulative doses over an average year range from 2760 to 3988 MEDs (7114 MEDs considering Canary Islands stations).

Abstract

An analysis is made of the UV Index (UVI) obtained from the ultraviolet erythemal solar radiation (UVER) data measured by the Spanish UVB Radiometric Network between the years 2000 and 2009. Previously, the daily UVI has been evaluated using two different criteria: (a) the value corresponding to solar noon; and (b) the daily maximum value. The mean percentage of agreement is 92% if we consider the cases for which the difference is zero or one UVI unit. These results are similar to those obtained in a previous work where only 2 years were analyzed.

In all the stations the UVI reaches very high values (8–10) in spring–summer, and the very high and extreme (⩾11) UVI values are more dependent on the continental effect than on the latitude effect. From the UVI values it is possible to classify the stations into four groups: Coastal stations, Continental stations (more than 200 km from the coast), Southern stations (Coastal stations but with similar values of UVI as the Continental ones due to their low latitude) and Canary Islands stations (1400 km southwest from the Iberian Peninsula thus lower latitude).

The monthly mean maximum of UVI is reached in July due to the annual evolution of the total ozone column. This value corresponds, for a skin phototype II, to three times the minimal erythemal dose (MED) in an hour in a Coastal station, 3.5 MEDs in an hour measured in a Continental or Southern station and up five MEDs in an hour in the Izaña station (Canary Islands).

The cumulative dose on a horizontal plane over an average year has been calculated for each station. More than 40% of the annual dose is received in summer, about 35% in spring, more than 11% in autumn and less than 10% in winter except for the stations in the Canary Islands where the difference between seasons is less significant.

Introduction

UV radiation causes many damaging effects [1], [2] on human beings, mainly in the skin [3], [4], [5], [6], [7], eyes [5], [8], [9], [10] and immune system [11], [12], [13]. The most common effect of overexposure to solar radiation is sunburn or erythema, which appears 10–16 h after exposure to natural sunlight [14], [15], [16]. At the same time, chronic skin overexposure to UV radiation provokes photo aging, which is characterized by wrinkles, loss of skin colour and elasticity [11], [17], [18], [19], [20].

Chronic skin overexposure to UV radiation also produces a number of premalignant cutaneous conditions [21], [22], [23]. In this sense, there is clear evidence that each of the three types of skin cancer (squamous cell carcinoma (SCC) [24], basal cell carcinoma (BCC) [25], and malignant melanoma) are caused by sun exposure. Thus, skin cancer cannot be only attributed to the increase of UV radiation due to the ozone layer depletion, but to the harmful effects of UVB radiation increased by other causes such as the extension of life, and popularization of sunbathing on the beaches. On the other hand, the beneficial effects of human exposure to ultraviolet radiation are rather scarce. The main benefit is the skin synthesis of vitamin D obtained as pro-vitamin D through diet [26], [27]. UV radiation is also utilized in the treatment of a number of skin diseases [28].

The CIE (Commission Internationale de l’Éclairage) adopted in 1987 a standard erythema action spectrum [29], marginally modified in 1998 [30], which is currently recommended for determining the UV erythemal radiation (UVER). The UVER is the spectrally integrated weighted solar irradiance at ground level with the spectral erythemal action curve proposed by the CIE.

The MED (Minimum Erythemal Dose) [31], [32] is the minimum dose of UVER that produces a noticeable reddening of a specific skin type (phototype) not exposed previously to solar radiation. Following the COST Action 713 [33], the European countries have adopted four skin types, shown in Table 1. The CIE also defined a Standard Erythemal Dose (SED) that corresponds to 100 J/m2 and does not depend on the skin type [34].

The global solar UV Index [35] is a recommendation of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) in collaboration with the WHO (World Health Organization), the WMO (World Meteorological Organization) and the UNEP (United Nations Environment Program) to forecast and to inform general public in a simple way about the UV doses that reach the ground. Specifically, the WMO [36] recommends that the UV Index should be quantitatively obtained by multiplying the UVER value (expressed in W/m2) by 40.

In this context, the UVB Radiometric Networks allow to study the UV radiation climatology, establish geographical and seasonal distributions of UV exposures and compare them with UVI forecast to minimize the impact of UV radiation on population and to adopt the necessary photo protection measures [37].

This article, which should be considered a continuation of a previous study published by the authors in 2002 [38], presents 10 year results (2000–2009) of measured values of the UV Index determined from the values of integrated UVER measured by the national UVB Radiation Network in Spain.

Section snippets

Materials and methods

The Spanish UVB Radiometric Network was created in 1998 by the State Agency of Meteorology (AEMET; formerly known as the National Institute of Meteorology [INM]), and nowadays it is composed by 26 stations which measure UVER and seven stations that also measure the total ozone in the atmospheric column. For this study, only the 16 original stations have been used [38], as only these have coincident databases spanning the 10 year period 2000–2009. Measurements are made every second, then averaged

Results and discussion

Two different criteria are used to determinate the UV Index for each day: (a) the value at solar noon, employed by the international community up to 1998; (b) the daily maximum 30 min averaged value, currently recommended by all the international organizations [35], [36].

An elementary statistical analysis has been used to compare the results given by the two criteria. For each station we have estimated the percentage of cases whose differences were zero, one, two, and three or more units of UVI (

Conclusions

We have analyzed 10 years of UV Index data in 16 stations of the Spanish UVB Radiometric Network. From the measurements of UV erythemal radiation we have obtained the daily UV Index. The difference between the UVI at noon and the maximum daily UVI is not significant as the authors showed in a previous work where 2 years were analyzed. Thus if we consider the cases for which the difference is zero or one UVI unit, the coincidence ranges from 89% (A Coruña) to 95% (El Arenosillo, Huelva), with an

Acknowledgements

This work was financed jointly by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund through projects CGL2011-24290 and CGL2012-33294, and by the Valencia Autonomous Government through the Project PROMETEO/2010/064. The collaboration of A.R. Esteve and V. Estellés was possible thanks to a postdoctoral fellowship of the VALi+d program by the Valencia Autonomous Government (APOSTD/2012/078), and a contract from the Juan de la Cierva program

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