Solar ultraviolet radiation: properties, characteristics and amounts observed in Brazil and South America

Abstract

The beneficial and harmful effects of human exposure to solar ultraviolet radiation (UV-R) are topics that arouse great interest not only among physicians and scientists, but also the general public and the media. Currently, discussions on vitamin D synthesis (beneficial effect) are confronted with the high and growing number of new cases of non-melanoma skin cancer and other diseases of the skin and eyes (harmful effect) diagnosed each year in Brazil. However, the lack of scientific knowledge on the UV-R in Brazil and South America leads to adoption of protective measures based on studies conducted in Europe and USA, where the amounts of UV-R available at surface and the sun-exposure habits and characteristics of the population are significantly different from those observed in Brazil. In order to circumvent this problem, the Brazilian Society of Dermatology recently published the Brazilian Consensus of Photoprotection based on recent studies performed locally. The main goal of this article is to provide detailed educational information on the main properties and characteristics of UV-R and UV index in a simple language. It also provides: a) a summary of UV-R measurements recently performed in Brazil; b) a comparison with those performed in Europe; and, c) an evaluation to further clarify the assessment of potential harm and health effects owing to chronic exposures.

FIGURE 1

Functions – biologic UV-R response for human beings. Erythema (red line), vitamin D synthesis (blue line) and nonmelanoma skin cancer (black line)

FIGURE 2

Spectral irradiance and UV-R absorption. Upper part – Simulation of spectral solar irradiance between 100 and 400 nm incident on the top of atmosphere (black line) and at the Earth’s surface (red line) for clear sky conditions (without clouds). Lower part – UV-R absorption in each wavelength, due to oxygen (in bands of wavelengths lower than 250 nm) and ozone

FIGURE 3

Temporal series of total ozone content in the atmosphere over five locations in the Southern hemisphere. Fortaleza/CE – 3.7°S; 38.5°W; São Paulo/SP – 23.5°S; 46.6°W; Porto Alegre/RS – 30.0°S; 51.2°W; Buenos Aires/Argentina – 34.6°S; 58.4°W; and, Base Com. .Ferraz/Antarctica – 62.1°S; 58.4°W). Data supplied by sensors/ satellites: OMI/Aura (operating since July/2004); TOMS/Earth Probe (July/1996 – December/2005); TOMS/Meteor-3 (August/1991 – November/1994) and TOMS/ Nimbus-7 (January/1978 – May/1993) s lower than 250 nm) and ozone Data obtained by backscattering UV satellite sensors - National Aeronautics and Space Administration (NASA).

FIGURE 4

UVB and UVA irradiance and the relationship between them. Upper part – UVB irradiance, on the left, and UVA irradiance, on the right (in Wm-2), typical of a clear sky day in summer solstice. Lower part – Composition of the radiation beam. Percentage of beam derived from direct (gray) and diffuse (white) radiation

FIGURE 5

Variability of UVB-R in relation to total UV-R during the year. Relative quantity of UVB-R (%) in total UV-R reaching the Earth’s surface in summer (December) and winter (July) solstices, and autumn (March) and spring (September) equinoxes. Simulations were based on average total ozone contents between the years 2004 and 2012 for the city of São Paulo/SP, considering clear sky conditions (no clouds)

FIGURE 6

Numerical UVI simulation at solar noon, for clear sky conditions (no clouds)

FIGURE 7

Boxplot of UVI reading databases. Readings taken around solar noon (one hour before and one hour after) in the cities of Paris (2011-2013)27 and São Paulo (2006- 2009),25. The circle indicates the average, the boxplots show the 5° and 95° percentile and the asterisk the maximum value found in the period