UV Index / UVA solar radiation ratio in Latin-America and antartic Peninsula. It’s relation to ozone depletion.

R D PIACENTINI, G M SALUM, C CAÑARTE, A IPIÑA, F STENGEL

Buenos Aires, Argentina

Congreso; 21st World Congress of Dermatology; 2007

Purpose of the study The UV index (UVI), a measure of skin risk to Sun exposure, is related with erythemal and non melanoma skin cancer (NMSC) solar irradiances. These irradiances have increased in the last two decades at middle and high latitudes of the Earth, due to the deterioration of the stratospheric ozone layer by contaminant gases [1]. Erythemal irradiance has been the subject of large amount of work, based on ground as well as on satellite instruments. Another important but less studied variable in relation to the skin, is the solar UVA irradiance. We analyzed the UVI / UVA ratio in Latin America and the Antarctic Peninsula and its correlation with the NMSC solar irradiance / UVA ratio. This has direct implications for dermatology in relation to suncreen protections. Method and Results The ozone layer depletion has occurred with a non-uniform distribution around the world [1]. From satellite data as well as from mathematical model calculations, we determined for highly populated Latin-America regions that the erythemal irradiance varies very little at intertropical latitudes. At middle and high latitudes, ozone depletion was more important than at intertropics, producing an increase of UVB and associated biological irradiances of several percents, but influenced very little the UVA component. However, this last solar radiation component, as well as the UVB, are influenced in a similar way by other factors, like changes in cloudiness (due to global warming for example), surface reflectivity and atmospheric microscopic particles called aerosols. Thus, the UVI / UVA ratio is essentially influenced by the ozone content of the atmosphere. Also, due to the significant ozone hole event that overpass several times per year Patagonia and the Antarctic Peninsula, a detailed analysis was made for these regions. A correlation function has been obtained between the UVI / UVA ratio and the NMSC solar irradiance / UVA ratio, in order to derive the latter from the former ratio. Conclusion The UVI / UVA ratio has been almost stable during the last two decades in the inter-tropical region of Latin-America (25ºN-25ºS) and increased with increasing latitude by several percents at middle-high latitudes (25ºS-60ºS). However, during the strong depletion event of the Antarctic ozone hole, changes of the atmospheric ozone content higher than 50% have been registered by the TOMS-NASA satellite and ground stations, producing similar changes in this ratio. So, in order to protect exposed humans correctly in these regions, the sunscreens must ensure adequate protection at these new levels. [1] WMO "Scientific Assessment of Ozone Depletion". Reports 2002 and 2006. [2] De Gruijl, F R and van der Leun J C. Estimate of the wavelength dependency of ultraviolet carcinogenesis and its relevance to the risk assessment of a stratospheric ozone depletion, Health Phys. 4, 317-323, 1994. [3] Madronich, S, www.acd.ucar.edu