Erythemal UVB Research Articles

Changes in surface UV solar irradiance and ozone over the balkans during the eclipse of August 11, 1999

Intensive measurements of UV solar irradiance, total ozone and surface ozone were carried out during the solar eclipse of 11 August 1999 at Thessaloniki, Greece and Stara Zagora, Bulgaria, located very close to the footprint of the moon's shadow during the solar eclipse with the maximum coverage of the solar disk reaching about 90% and 96% respectively. It is shown that during the eclipse the diffuse component is reduced less compared to the decline of the direct solar irradiance at the shorter wavelengths. A 20-minute oscillation of erythemal UV-B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20-minute fluctuation in total ozone presumably caused by the eclipse induced gravity waves. The surface ozone measurements at Thessaloniki display a decrease of around 10–15 ppbv during the solar eclipse. Similarly, ozone profile measurements with a lidar system indicate a decrease of ozone up to 2 km during the solar eclipse. The eclipse offered the opportunity to test our understanding of tropospheric ozone chemistry. The use of a chemical box model suggested that photochemistry can account for a significant portion of the observed surface ozone decrease.

A variação sazonal da radiação ultravioleta solar biologicamente ativa

Series temporais de radiacao UV-B, biologicamente ativa, obtidas em varios locais no Brasil, em Punta Arenas no Chile e em La Paz na Bolivia sao apresentadas. O quadro atual de mudanca atmosferica, principalmente a tendencia global de reducao no ozonio total, fez surgir na comunidade cientifica preocupacoes quanto a um possivel aumento na intensidade da radiacao ultravioleta (UV) solar na superficie terrestre. Nesse contexto, o Instituto Nacional de Pesquisas Espaciais-INPE opera uma rede de medidores do tipo Biometro, radiometros especialmente projetados para medir a radiacao UV causadora de efeitos danosos a saude humana, a radiacao UV-B Eritema, desde o inicio dos anos 1990. Analisam-se neste trabalho as series temporais de maxima dose diaria de radiacao UV-B Eritema obtidas com o Biometro, estudando-se a variacao sazonal e calculando-se o Indice UV. Os maiores valores do Indice UV sao encontrados nas regioes de La Paz, Campo Grande e Natal. A radiacao UV-B apresentou uma forte dependencia da latitude geografica e da altitude, conforme esperado. Os Indices UV atingiram valores proximos a 15 em La Paz, e acima de 12 em Natal e Campo Grande no periodo de verao. Tambem e apresentado o resultado de um experimento para medir a radiacao UV-B difusa realizado em Cachoeira Paulista em 24 e 25 de novembro de 1998. A radiacao difusa representa pelo menos 45% da radiacao global para o UV-B Eritema.

Biological effectiveness of solar UV radiation in humans.

Solar UVB radiation is prejudicial to the health of humans in a number of ways. Erythema and photodermatoses are acute reactions of the skin; keratitis and conjunctivitis are acute reactions of the eye. Various types of skin cancer, accelerated aging of the skin, and cataract formation in the crystalline lens are reactions that appear with great latency. UV radiation can also cause damage to the immune system and DNA. For the period 1981-1991, an increase in erythemal effective UVB radiation of +(7 +/- 4)% per decade was measured in a non-polluted high mountain area (Jungfraujoch, 3576 m a.s.l., Switzerland). This increase is related to a decrease in stratospheric ozone. The effects on human health are discussed. A 10% ozone reduction increases non-melanoma skin cancer by 26% and cataract by 6 to 8%.

ATMOSPHERIC SUN PROTECTION FACTOR ON CLEAR DAYS: ITS OBSERVED DEPENDENCE ON SOLAR ZENITH ANGLE AND ITS RELEVANCE TO THE SHADOW RULE FOR SUN PROTECTION

Global irradiances measured in seven 5-nm bands of UV-B at Rockville, MD (39.1 degrees N, 77.1 degrees W) on 28 clear days near the summer solstice are convoluted with the erythemal action spectrum of human skin to determine dose rates at various hours of the day. These rates are averaged with respect to solar zenith angle to obtain the diurnal variation of mean dose rate and of the Sun Protection Factor (SPF) of the atmosphere (reciprocal of the normalized atmospheric transmissivity) on a typical clear summer day in Rockville. At a 45 degrees zenith angle the atmospheric SPF is computed to be 2.7 and increases rapidly to greater than 7 at 60 degrees. Dose rates are integrated with respect to time to obtain estimates of mean doses for various periods during clear days at Rockville in mid summer and near the autumnal equinox. In mid summer the effective erythemal UV-B exposure during the period when the solar zenith angle is less than 45 degrees is about five times greater than that during the remainder of the day. These observations provide scientific basis for a shadow rule for solar UV-B protection: when shadows are shorter than objects casting them, sunburn is much more likely than at other times.

Transforming Growth Factor α: In vivo Release by Normal Human Skin following UV Irradiation and Abrasion

Transforming growth factor alpha (TGF alpha) is a keratinocyte-growth-stimulating factor which may have a role in epidermal hyperproliferation, psoriasis, and wound healing. Since increased epidermal proliferation occurs in response to UV radiation, we have measured the amount of TGF alpha in exudates from normal and UVB-irradiated human skin. Cutaneous exudates were obtained using the skin chamber abrasion technique from one side of the back of volunteers (n = 10) with normal skin (collected following skin contact times of 2 and 30 min). Exudates were similarly obtained from the contralateral side of the back at sites irradiated 2 h previously with 3 x the minimum erythemal dose UVB. Levels of TGF alpha were measured by radioimmunoassay. Normal human skin released TGF alpha immediately after abrasion: unirradiated, 63 +/- 18 ng/ml; irradiated, 89 +/- 15 ng/ml. Levels of TGF alpha increased within 30 min to 110 +/- 14 ng/ml in unirradiated skin and to 190 +/- 17 ng/ml in irradiated skin. Irradiated sites at 30-min time points were significantly higher (p less than 0.05) than all other samples. The presence of releasable TGF alpha in normal skin suggests a role for TGF alpha in wound repair mechanisms.