Photochemical & Photobiological Sciences PAPER Received 21st May 2016, Accepted 2nd April 2017 DOI: 10.1039/c6pp00161k rsc.li/pps Ultraviolet solar radiation in the tropical central Andes (12.0°S)† Luis F. Suárez Salas, a Jose L. Flores Rojas, * b Augusto J. Pereira Filho c and Hugo A. Karam d Ultraviolet (UV) solar irradiance measurements performed in the central Andes, Huancayo, Peru (12.0°S, 75.3°W, 3313 m asl) at 1 min intervals between January 2003 and December 2006 were used to analyse daily, monthly, and annual cycles of UV solar irradiance. The measurements were performed using a GUV-511 multi-channel filter radiometer at four wavelengths: 305, 320, 340, and 380 nm. UV irradiance data under clear sky and all sky conditions were separated using a procedure based on calculation of nor- malized irradiance. In February, the highest hourly mean value at noon for the UV Index reached 18.8 for clear sky conditions and 15.5 for all sky conditions, with outlier peaks close to UVI = 28. In addition, the highest mean value for the daily erythemal dose was found also in February, reaching 7.5 kJ m -2 d -1 with a maximum outlier value close to 10.1 kJ m -2 d -1 . Comparisons between the clear sky GUV measure- ments and TUV model estimations were evaluated with statistical quantities showing values of R 2 close to 0.98. The total ozone column and trace gases were obtained from OMI. The aerosol parameters were obtained from MODIS. The enhancements due to clouds of spectral irradiance at 340 nm as compared to a cloudless sky reach maxima of 20%. These results indicate that tropical central Andes has among the highest incident ultraviolet solar radiation in the world. 1. Introduction Solar radiation is fundamental to maintain life over the Earth’s surface. The main solar energy radiation spectra include visible, infrared, gamma, X-rays, and ultraviolet (UV) wavelengths. The latter is a small fraction but an important one, with wavelengths ranging from 100 to 400 nm. 1 For better understanding and research, UV radiation was divided into three regions: UV-A (315 to 400 nm), UV-B (280 to 315 nm), and UV-C (100 to 280 nm). UV-B, although it has a narrow band, could produce important biological effects 2 and is strongly absorbed by the ozone layer. UV-C (100 to 280 nm) represents the most harmful radiation, but it is mostly removed by the atmosphere’s components, mainly by atmos- pheric oxygen (O 2 ) and ozone (O 3 ). 3 The ultraviolet radiation index (UV Index) has been implemented for public information of UV radiation intensity at Earth’s surface as related to skin damage. The UV Index is 40 times the solar irradiance weighted by the erythema action spectrum (W m -2 ). 4 In addition, the UV Index is a good in- dicator of the possible consequences of sun exposure in terms of producing different types of skin damage and is an impor- tant awareness tool among the public to protect them against excessive exposure to UV radiation. 5 In Peru, there is an acceptable level of awareness about the risks of sun exposure. However, a large proportion of the popu- lation fails to incorporate regular solar protection as a practice in their daily life. 6 Of all the types of skin cancer in Peru, 64.9% were basal cell carcinoma, 26.7% were cutaneous mela- noma, and 8.4% were squamous cell carcinoma. 7 Descriptors and health messages associated with the UV Index scale are targeted towards European or Asian skin types, and UV exposure categories that were developed in Canada and endorsed by WHO, WMO, UNEP, and ICNRP 5 classify an “extreme” UV Index as values higher than 11. However, this categorization is not directly applicable to the population living closer to the equator, in particular for those in the high- altitude Andes region of South America. In this context, discussions at the Latin American Society of Photobiology and Photomedicine’s Congress, which was held in Arequipa, Peru, in November 2013, recommended contin- † Electronic supplementary information (ESI) available: Annual cycle of UV radi- ation in the central Andes (12°S). See DOI: 10.1039/C6PP00161K a Observatorio de Huancayo del Instituto Geofísico del Perú, Calle Badajoz 169, Ate, Lima, Perú. E-mail: lsuarez@igp.gob.pe b Universidade de São Paulo – USP/IAG/DCA – Rua do Matão, 1226, São Paulo, SP, Brasil. E-mail: joseflores@model.iag.usp.br c Universidade de São Paulo – USP/IAG/DCA – Rua do Matão, 1226, São Paulo, SP, Brasil. E-mail: apererira@model.iag.usp.br d Universidade Federal de Rio de Janeiro, Rio de Janeiro - UFRJ/IGEO/CCMN. Rua Athos da Silveira Ramos, 274, Cidade Universitária - Ilha do Fundão, Rio de Janeiro, RJ, Brasil. E-mail: hugo@igeo.ufrj.br 954 | Photochem. Photobiol. Sci. , 2017, 16, 954–971 This journal is © The Royal Society of Chemistry and Owner Societies 2017