Availability of vitamin D photoconversion weighted UV radiation in southern South America.

Ultraviolet radiation (UVR) plays a key role in several biological functions, including human health. Skin exposure to UVR is the main factor in vitamin D photoconversion. There is also evidence relating low levels of vitamin D with certain internal cancers, mainly colon, breast and prostate, as well as other diseases. Several epidemiological studies have shown an inverse relationship between the above-mentioned diseases and latitude, in accordance with the ultraviolet radiation latitudinal gradient. The aim of this study is to determine whether UV irradiance levels in the southern South America are sufficient to produce suitable levels of vitamin D year around. For this purpose, vitamin D photoconversion weighted-irradiance was analyzed between S.S. de Jujuy (24.17°S, 65.02°W) and Ushuaia (54° 50'S, 68° 18'W). In addition to irradiance, skin type and area of body exposed to sunlight are critical factors in vitamin D epidemiology. Due to a broad ethnic variability, it was assumed that the skin type in this region varies between II and V (from the most to the less sensitive). All sites except South Patagonia indicate that skin II under any condition of body area exposure and skin V when exposing head, hands, arms and legs, would produce suitable levels of vitamin D year round (except for some days in winter at North Patagonian sites). At South Patagonian sites, minimum healthy levels of vitamin D year round can be reached only by the more sensitive skin II type, if exposing head, hands, arms and legs, which is not a realistic scenario during winter. At these southern latitudes, healthy vitamin D levels would not be obtained between mid May and beginning of August if exposing only the head. Skin V with head exposure is the most critical situation; with the exception of the tropics, sun exposure would not produce suitable levels of vitamin D around winter, during a time period that varies with latitude. Analyzing the best exposure time during the day in order to obtain a suitable level of vitamin D without risk of sunburn, it was concluded that noon is best during winter, as determined previously. For skin type II when exposing head, exposure period in winter varies between 30 and 130 min, according to latitude, except for South Patagonian sites. During summer, noon seems to be a good time of day for short periods of exposure, while during leisure times, longer periods of exposure without risk of sunburn are possible at mid-morning and mid-afternoon. At 3 h from noon, solar zenith angles are almost the same for sites between the tropics and North Patagonia, and at 4 h from noon, for all sites. Then, in these cases, the necessary exposure periods varied slightly between sites, only due to meteorological differences.

Quality of UVR exposure for different biological systems along a latitudinal gradient.

The exposure of organisms to ultraviolet radiation (UVR) is characterized by the climatology (annual cycle) and the variance (anomalies) of biologically-weighted irradiances at eight geographical locations in austral South America, from 1995-2002. The net effect of UVR on biological systems is a result of the balance of damage and repair which depends on intensity and duration of irradiance and is modulated by its variability. The emphasis in this study is on day-to-day variability, a time scale of importance to adaptive strategies that counteract UVR damage. The irradiances were weighted with DNA- and phytoplankton photosynthesis-action spectra. Low latitude sites show high average UVR. For all sites, the frequency of days with above average irradiances is higher than below average irradiances. Persistence in anomalies is generally low (

Multichannel radiometer calibration: a new approach.

The error in irradiance measured with Sun-calibrated multichannel radiometers may be large when the solar zenith angle (SZA) increases. This could be particularly detrimental in radiometers installed at mid and high latitudes, where SZAs at noon are larger than 50 degrees during part of the year. When a multiregressive methodology, including the total ozone column and SZA, was applied in the calculation of the calibration constant, an important improvement was observed. By combining two different equations, an improvement was obtained at almost all the SZAs in the calibration. An independent test that compared the irradiance of a multichannel instrument and a spectroradiometer installed in Ushuaia, Argentina, was used to confirm the results.

[Ultraviolet radiation producing erythema in Valdivia. A comparison among satellite data, a radiative transfer model and ground-based observations]. / Radiación ultravioleta productora de eritema en Valdivia. Comparación entre inferencias satelitales, modelo de transferencia radiativa y mediciones desde Tierra.

To evaluate dose rates and daily doses (DDE) at Valdivia in Southern Chile, ultraviolet irradiances recorded every 15 min from 1998 to 2000 with a high resolution spectroradiometer were weighted with an erythemal action spectrum. Exposure times to get one MED (210 J/m2) in Summer are 10, 12, 18 and 24 min for skin types I trough IV respectively. DDE estimations included in NASA Web products overestimate measurements by 16% on average in Summer, with an absolute uncertainty of 980 J/m2 at the 95% level. Observed dose rates for clear days are in fair agreement with the numerical output from a numerical model, suggesting that acute episodes can be predicted if total ozone can be forecasted and the population is instructed on corrections for cloud effects.

Radiación ultravioleta en Chile: variaciones con la altura y la latitud / Ultraviolet radiation in Chile: variations with altitude and latitude

Chile tiene un territorio continental ubicado entre los 18º-56º de latitud sur y abarcan zonas entre el nivel del mar y los 5.000 metros de altura. Sus habitantes deben viajar a lo largo y ancho del territorio, ya sea por razones de negocios, oportunidades de trabajo, deportes o turismo, por lo cual están constantemente sometidos a variaciones del régimen de radiación ultravioleta. El objetivo de esta presentación es ofrecer una visión preliminar de las dosis diarias de eritema (DDE) a lo largo y ancho del país. Con un radiómetro portátil de cuatro canales en el UV se realizaron mediciones desde la salida hasta la puesta del sol en diferentes lugares entre los 18º y 53º S) en invierno y verano. A través del método de inversión se recuperó el espectro UV completo, minuto a minuto en pocos días de cada lugar de medición. Usando el espectro de acción (CIE) para eritema fueron estimadas las dosis diarias. Se comparan los valores de DDE de los lugares analizados para obtener un primer vistazo de los cambios debidos a latitud y altura. En general, los cambios por diferencias de altura o latitud son mayores en invierno que en verano. por otra parte, las personas que se desplazan 1.000 km de sur a norte en invierno se someten a un mayor estrés que si suben 1.000 metros en la cordillera