Erythemal UV Doses Research Articles

Reconstruction and variability of high daily erythemal ultraviolet doses and relationship with total ozone, cloud cover, and albedo in Novi Sad (Serbia)

AbstractIn this paper, a method previously developed for reconstructing daily erythemal ultraviolet (UVery) doses in Novi Sad (Serbia) was improved and used for estimating daily UVery over the period 1971–2018. The proposed new method uses reanalysed total ozone column (TOC) data and snow cover as an input and is based on the empirical relationship between relative sunshine duration and relative UVery doses. Introducing reanalysed TOC data and snow cover data significantly improved the quality and accuracy of the reconstructed UVery time series, particularly in the winter season. The reconstructed time series revealed the statistically significant increase in summer and winter UVery in the 1980s and the first half of the 1990s (+8.78% and + 13.14% per decade, respectively), which was linked to the statistically significant decline in TOC (−4.13 and −7.36% per decade, respectively). The study focuses on days with high erythemal UV dose (highUVery), which is defined based on the 90th percentile of the daily UVery for each month. Moreover, the influence of low TOC, low cloud cover conditions, and high surface albedo on highUVery was analysed on a seasonal basis. The results of this study show that highUVery days increased from the 1980s, particularly strongly in the period of TOC depletion. A fraction of highUVery days in the last two decades was large (12.29%), which is higher than in the previous periods (6.97 and 8.68% in the period before and during TOC depletion, respectively). The occurrence of highUVery days was influenced mostly by low cloud cover (89.71% of days), and low TOC (82.23% of days). In the winter season, high surface albedo influenced the appearance of 19.18% of highUVery days. However, overall the interaction of low cloud cover and low TOC in all seasons most often led to the appearance of highUVery days.

Estimations of the Erythemal UV Doses and the Amount of the Sun-Synthesized Vitamin D by Adults during the Cruise to Spitsbergen–Polar Measurement Campaign (2–21 July 2017)

UV index (UVI) measurements were carried out by the hand-held instrument Solarmeter 6.5 onboard of MS Horyzont II during the cruise from Poland (Gdynia) to Spitsbergen (and back) in the period from 2 to 21 July 2017. A method is proposed to estimate the erythemal doses and sun-synthesized amount of vitamin D from a limited number of daily UVI observations. This study shows that the erythema could appear in a person with Caucasian type of skin characterized by Minimum Erythema Dose (MED) ~250 J m−2 after ~1 h exposure near the polar circle and up to few hours in the Svalbard. During this time, it was possible to get the dose of vitamin D3 equivalent to ~1000 IU of oral intake. The protection against UV overexposure should be applied even if UVI values during the cruise in the Arctic were always below the World Meteorological Organization (WMO) warning threshold of 3. To provide adequate amount of vitamin D, the exposure should be continued until getting 1 MED, after which the vitamin supplementation (or a diet rich in vitamin D) is necessary.

Exposome extrinsic factors in the tropics: The need for skin protection beyond solar UV radiation

Environmental factors such as solar ultraviolet radiation (UV), air pollution, and variations in the air temperature (T) and relative humidity (RH) affect skin health. However, it is still unclear what effects on the skin may occur as the result of these combined exposures. This study was designed to quantify environmental exposures during routine daily activities to provide quantitative metrics that inspire future studies on exposome and human health. Two bicyclists were equipped with instruments to collect specific data concerning UV (at different angles), T, RH, ground-level ozone (O3), and chemical exposures. Measurements were conducted in the summer and winter seasons of 2016–2017 in four touristic and urban Brazilian cities. Erythemal UV doses (EryD) exceeding the minimal erythemal doses (MED) for phototype V (EryD > 600 Jm−2) were registered in most tours, including cloudy weather and during the winter. Significant EryD were also observed in tilted body parts. Humidex Index (HI) higher than 30 °C revealed great thermal discomfort in most regions, mainly during the summer. O3 amounts were generally below the thresholds established by the World Health Organization (WHO), except for two instances in which the peak of O3 concentrations exceeded the 100 μg m−3. More than 10% of chemicals sampled during the tours were identified as Polycyclic Aromatic Hydrocarbons (PAH), including anthracene (peak of 207 ng per gram of air). There was a combination of EryD exceeding the MED, thermal discomfort, and PAH exposure in most studied areas. We concluded that this exposome could accelerate and amplify skin-related damages generally associated with a single environmental factor exposure, such as sunlight exposure at any time of the year, for example.

Occupational Exposure to Solar UV Radiation of a Group of Fishermen Working in the Italian North Adriatic Sea.

Occupational solar radiation exposure is a relevant heath risk in the fishing sector. Our aim was to provide a detailed evaluation of individual UV exposure in three different fishing activities in Italy, with personal UV dosimeters and a simple formula to calculate the fraction of ambient erythemal UV dose received by the workers. The potential individual UV exposure of the fishermen was between 65 and 542 Joules/m2. The percentages of the ambient exposure were estimated between 2.5% and 65.3%. Workers’ UV exposure was mainly influenced by the characteristics of the work activity, the postures adopted, and the type of boats. Overall, our data showed that 43% of the daily measurements could result largely above the occupational limits of 1–1.3 standard erythemal dose (i.e., 100 Joules/m2) per day, in case of exposure of uncovered skin areas. Measurements of individual UV exposure are important not only to assess the risk but also to increase workers’ perception and stimulate the adoption of preventive measures to reduce solar UV risk. Furthermore, the simple method proposed, linking ambient erythemal UV dose to the workers’ exposure, can be a promising tool for a reliable assessment of the UV risk, as time series of environmental UV dose are widely available.

Reconstruction of the erythemal UV radiation data in Novi Sad (Serbia) using the NEOPLANTA parametric model

This paper focuses on the development and application of a technique for filling the daily erythemal UV dose data gaps and the reconstruction of the past daily erythemal UV doses in Novi Sad, Serbia. The technique implies developing the empirical equation for estimation of daily erythemal UV doses by means of relative daily sunshine duration under all sky conditions. A good agreement was found between modeled and measured values of erythemal UV doses. This technique was used for filling the short gaps in the erythemal UV dose measurement series (2003–2009) as well as for the reconstruction of the past time-series values (1981–2002). Statistically significant positive erythemal UV dose trend of 6.9 J m−2 per year was found during the period 1981–2009. In relation to the reference period 1981–1989, an increase in the erythemal UV dose of 6.92 % is visible in the period 1990–1999 and the increase of 9.67 % can be seen in the period 2000–2009. The strongest increase in erythemal UV doses has been found for winter and spring seasons.

Occupational UV Exposure of Environmental Agents in Valencia, Spain

Excessive exposure to ultraviolet radiation (UVR) is considered the most important environmental risk factor in the development of melanoma and skin cancer. Outdoor workers are among those with the highest risk from exposure to solar UVR, as their daily activities constantly expose them to this radiation source. A study was carried out in Valencia, Spain, in summer 2012 and involved a group of 11 workers for a period of six 2-day recordings. Sensitive spore-film filter-type personal dosimeters (VioSpor) were used to measure erythemal UVR received by environmental agents in the course of their daily work. Median 2-day UV exposure was 6.2 standard erythema dose (SED), with 1 SED defined as effective 100 J m(-2) when weighted with the Commission Internationale de L'Eclairage's (CIE) erythemal response function. These workers were found to receive a median of 8.3% total daily ambient ultraviolet erythemal radiation. Comparison with the occupational UV exposure limit showed that the subjects had received an erythemal UV dose in excess of occupational guidelines, indicating that protective measures against this risk are highly advisable.

Aerosol Modulation of Ultraviolet Radiation Dose over Four Metro Cities in India

This paper discusses the influence of aerosols on UV erythemal dose over four metro cities in India. Tropospheric Emission Monitoring Internet Service (TEMIS), archived UV-index (UV-I), and UV daily erythemal dose obtained from SCIAMACHY satellite were used in this study during June 2004 and May 2005 periods covering four important Indian seasons. UV-Index (UV-I), an important parameter representing UV risk, was found to be in the high to extreme range in Chennai (8.1 to 15.33), moderate to extreme range in Mumbai and Kolkata (5 to 16.5), and low to extreme over Delhi (3 to 15). Average UV erythemal dose showed seasonal variation from 5.9 to 6.3 KJm−2during summer, 2.9 to 4.4 KJm−2during postmonsoon, 3 to 4.5 KJm−2during winter, and 5.1 to 6.19 KJm−2during premonsoon seasons over the four cities. To estimate the influence of aerosols on reducing UV dose, UV aerosol radiative forcing and forcing efficiency were estimated over the sites. The average aerosol forcing efficiency was found to be from-1.38±0.33to-3.01±0.28 KJm−2AOD−1on different seasons. The study suggests that aerosols can reduce the incoming UV radiation dose by 30–60% during different seasons.

Doses of erythemal ultraviolet radiation observed in Brazil

Non-melanoma skin cancer represents a quarter of the new cancer cases detected in Brazil. Despite the importance of this issue to public health, there are deficits in knowledge on the local UV radiation levels among physicians. In this work, we evaluate a set of daily erythemal UV doses measured in different Brazilian locations. Very high erythemal UV doses that often exceeded safe amounts were observed over almost the whole year, even during the time interval usually recommended as safe (before 10:00h and after 16:00h). These findings will hopefully enable foreign tourists, dermatologists, and decision-makers to implement new measures for solar protection according to South American standards.

Spatial Distribution and Temporal Variation of Solar UV Radiation over the Tibetan Plateau

The Tibetan Plateau has very high levels of ultraviolet radiation. To study the UV radiation across the Tibetan Plateau, data from the TOMS (Total Ozone Mapping Spectrometer) satellite for the periods 1979 -1992 and 1997–¬ 2003 are used. The analysis shows a 21-year average of the spatial distribution of daily summer erythemal UV doses across the Tibetan Plateau and its vicinity with a spatial resolution of 1° Lat. - 1.25° Long., also obtains temporal variations during the period 1979 ¬- 2003 of UV radiation for the region by selecting seven locations across the Tibetan Plateau and its neighboring areas. The results show that during the summer months from May to August the average daily erythemal UV doses at the selected seven sites across the Tibetan Plateau range from 7.5 to 9.0 kJ/m2. These daily erythemal UV doses are considerably higher than those observed at geographically close, lower-altitude locations such as Chengdu in China and New Delhi in India, which had corresponding values of 4.1 kJ/m2 and 5.8 kJ/m2, respectively. During the period from 1979 to 1992 observe a clear trend of increasing erythemal UV doses over the Tibetan Plateau. Comparisons between satellite derived UV radiation and ground-based measurements of UV radiation for Lhasa are made.

On the usability of the ERA‐40 reanalysis in the estimation of past surface UV radiation over Europe

Erythemal daily UV doses have been calculated using input data from the ERA‐40 reanalysis for years 1958–2002. The quality of input parameters for UV calculations has been validated with available ground based total ozone data and estimates of Cloud Modification Factor (CMF), and the results have been compared with existing UV data. Owing to limited availability of validation data especially during 1960s and 1970s the analysis focused on sites located in central and northern Europe. The current work is the first step in deriving reliable long‐term UV time series from the ERA‐40 reanalysis. Total ozone from the ERA‐40 reanalysis is affected by significant biases, especially before satellite ozone measurements were available for assimilation. Estimations of the effect of clouds on surface UV were made using global radiation (300–3000 nm) budgets at the surface because available ERA‐40 cloud data do not allow good estimates of surface daily UV doses. There are some problems with ERA‐40 solar radiation budgets which cause systematic biases in calculated daily UV doses. Comparison of calculated daily erythemal UV doses against ground‐based UV data indicate that ERA‐40 UV doses are typically overestimated by 6–18% in central and northern Europe and underestimated by 9–17% at Davos, Switzerland. Root‐mean‐square errors of the calculated daily UV doses are usually in the range of 30–40%. Trends of UV doses were calculated for the concurrent period of the TOMS satellite UV data (1979–2002). The trends of zonally averaged ERA‐40 and TOMS UV agree well and are mostly of the same sign and magnitude.

Analysis of Ozone (O3) and Erythemal UV (EUV) measured by TOMS in the equatorial African belt

We presented time series of total ozone column amounts (TOCAs) and erythemal UV (EUV) doses derived from measurements by TOMS (Total Ozone Mapping Spectrometer) instruments on board the Nimbus-7 (N7) and the Earth Probe (EP) satellites for three locations within the equatorial African belt for the period 1979 to 2000. The locations were Dar-es-Salaam (6.8° S, 39.26° E) in Tanzania, Kampala (0.19° N, 32.34° E) in Uganda, and Serrekunda (13.28° N, 16.34° W) in Gambia. Equatorial Africa has high levels of UV radiation, and because ozone shields UV radiation from reaching the Earth’s surface, there is a need to monitor TOCAs and EUV doses. In this paper we investigated the trend of TOCAs and EUV doses, the effects of annual and solar cycles on TOCAs, as well as the link between lightning and ozone production in the equatorial African belt. We also compared clear-sky simulated EUV doses with the corresponding EUV doses derived from TOMS measurements. The TOCAs were found to vary in the ranges 243 DU − 289 DU, 231 DU − 286 DU, and 236 DU − 296 DU, with mean values of 266.9 DU, 260.9 DU, and 267.8 DU for Dar-es-Salaam, Kampala and Serrekunda, respectively. Daily TOCA time series indicated that Kampala had the lowest TOCA values, which we attributed to the altitude effect. There were two annual ozone peaks in Dar-es-Salaam and Kampala, and one annual ozone peak in Serrekunda. The yearly TOCA averages showed an oscillation within a five-year period. We also found that the EUV doses were stable at all three locations for the period 1979−2000, and that Kampala and Dar-es-Salaam were mostly cloudy throughout the year, whereas Serrekunda was mostly free from clouds. It was also found that clouds were among the major factors determining the level of EUV reaching the Earth´s surface. Finally, we noted that during rainy seasons, horizontal advection effects augmented by lightning activity may be responsible for enhanced ozone production in the tropics.

Relationship between high daily erythemal UV doses, total ozone, surface albedo and cloudiness: An analysis of 30 years of data from Switzerland and Austria

This work investigates the occurrence frequency of days with high erythemal UV doses at three stations in Switzerland and Austria (Davos, Hoher Sonnblick and Vienna) for the time period 1974–2003. While several earlier studies have reported on increases in erythemal UV dose up to 10% during the last decades, this study focuses on days with high erythemal UV dose, which is defined as a daily dose at least 15% higher than for 1950s clear-sky conditions (which represent preindustrial conditions with respect to anthropogenic chlorine). Furthermore, the influence of low column ozone, clear-sky/partly cloudy conditions and surface albedo on UV irradiance has been analyzed on annual and seasonal basis. The results of this study show that in the Central Alpine Region the number of days with high UV dose increased strongly in the early 1990s. A large fraction of all days with high UV dose occurring in the period 1974–2003 was found especially during the years 1994–2003, namely 40% at Davos, 54% at Hoher Sonnblick and 65% at Vienna. The importance of total ozone, clear-sky/partly cloudy conditions and surface albedo (e.g. in dependence of snow cover) varies strongly among the seasons. However, overall the interplay of low total ozone and clear-sky/partly cloudy conditions led to the largest fraction of days showing high erythemal UV dose. Furthermore, an analysis of the synoptic weather situation showed that days with high erythemal UV dose, low total ozone and high relative sunshine duration occur at all three stations more frequently during situations with low pressure gradients or southerly advection.

The PROMOTE UV Record: Toward a Global Satellite-Based Climatology of Surface Ultraviolet Irradiance

This paper describes the PROMOTE UV Record, which aims to provide a global long-term record of the surface UV radiation. The algorithm developed takes as input cloud information from the International Satellite Cloud Climatology Project (ISCCP) and a recently developed multisensor assimilated record of the total ozone column. Aerosols and surface albedo are based on climatologies. Here, first validation results of the PROMOTE UV Record are presented through comparison against ground-based measurements of daily erythemal UV doses at eight European stations. The validation shows that the method is working reasonably, although there is a clear tendency toward overestimation. Typically, the median bias as compared to measurements is 3%-10% and 56%-68% of the daily doses are within plusmn20% from the ground-based reference. The prototype version of the PROMOTE UV Record included in this paper covers the period from July 2002 to June 2005. The time series will later be extended to start in 1983.

Time series of daily erythemal UV doses at Uccle, Belgium

The relation of the daily doses of erythemal UV at Uccle with total solar irradiation, total ozone column and the aerosol optical depth in the UV are investigated together with trends in these atmospheric parameters for the period 1990 to March 2007. It is shown that the trend in UV radiation is negative in January, August and December and positive the rest of the year. The correlations with total solar radiation, total ozone and aerosol optical depth at 320 nm are in the range of 0.90 to 0.99, −0.2 to −0.5 and −0.0 to −0.3, respectively. However the UV daily dose changes with up to 1.5% for a 1% change in total solar radiation, with −0.8% for a 1% change in aerosol optical depth and with only −0.1% for a 1% change in ozone, indicating the importance, on the short time-scale, of changes in aerosol properties for the UV irradiance reaching the surface.

Reconstruction of erythemal UV-doses for two stations in Austria: a comparison between alpine and urban regions

Abstract. The aim of this study is the reconstruction of past UV-doses for two stations in Austria, Hoher Sonnblick and Vienna, using a physical radiation transfer model. The method uses the modeled UV-dose under clear-sky conditions, cloud modification factors and a correction factor as input variables. To identify the influence of temporal resolution of input data and modification factors, an ensemble of four different modelling approaches was calculated, each with hourly or daily resolution. This is especially important because we found no other study describing the influence of the temporal resolution of input data on model performance. Following the results of the statistical analysis of the evaluation period the model with the highest temporal resolution (HMC) was chosen for the reconstruction of UV-doses. A good agreement between modelled and measured values of erythemally effective UV-doses was found at both stations. In relation to the reference period 1976–1985 an increase in the erythemal UV-dose in Vienna of 11% is visible in the period 1986–1995 and an increase of 17% in the period 1996–2005 can be seen. At Hoher Sonnblick the corresponding increase is 2% and 9%. For the different seasons the strongest increase in erythemal UV-dose has been found for winter and spring season at both stations. Further the influences of total ozone and cloudiness on changes in erythemal UV-doses were analyzed. This analysis showed for both stations, that changes in total ozone had a larger influence on erythemal UV-doses than changes in cloudiness.

Seasonal Erythemal UV Doses in Belo Horizonte, Brazil

The ultraviolet radiation (UVR) emitted by the Sun causes many effects on the biosphere. On human beings they vary from the benefit of vitamin D synthesis to the harm of skin cancer induction. The biological dose depends on the effect, the exposure time to the Sun and the amount of UVR received. In this work we show that the measured incidence of erythemal dose (ED) in Belo Horizonte (19.92 degrees S, 43.94 degrees W, 858 m a.s.l., Brazil) for a cloudless day can vary from 7503 to 2926 J m(-2) in the summer-winter seasonal variation. In addition, supposing a linear relationship between the ED and the geophysical parameters of solar zenith angle cosine (cos(SZA)), column ozone and reflectivity from the ozone monitoring instrument overpass measurements, a model for the forecast of UVR incidence on a monthly-based period is developed. From this an annual ED of 1,451,099 J m(-2) is obtained.

UV measurements in the 3000–5000 m altitude region in Tibet

We present measurements of solar UV radiation performed with multichannel moderate‐bandwidth NILU‐UV filter instruments during winter and summer in 2003 in the altitude region from 3000 m to 5000 m at 29°N in the Lhasa region in Tibet. During summer the UV index was found frequently to exceed 15 on clear days and occasionally to exceed 20 on partially cloudy days. High altitudes, low ozone column amounts, clean atmospheres, and relatively low latitudes are factors that contribute to the high UV levels on the Tibetan plateau. UV index values of 12 were measured in late winter for a solar zenith angle of 40° at a snow‐covered 5000 m altitude site. This is a 35% increase compared to a corresponding snow‐free surface. Our measurements show that the solar UV radiation increases with altitude. For clear‐sky and snow‐free conditions the altitude increase is 7–8% per km for erythemal UV dose rates and 3% per km at a wavelength of 340 nm. Results from clear‐sky calculations using a multiple‐scattering radiative transfer model were found to agree within 5% with clear‐sky UV measurements. Radiative transfer calculations combined with measurements were used to estimate the influence of clouds on the UV radiation at the surface. On the average the variable cloud cover in Lhasa reduced the daily integrated erythemal UV dose by 25%. The NILU‐UV instruments also provide total ozone column amounts. The mean difference between daily total ozone column amounts derived from NILU‐UV measurements and from Earth Probe TOMS data was −1.4% ± 3.2% (1σ).

Proxy-based reconstruction of erythemal UV doses over Estonia for 1955–2004

Abstract. A proxy-based reconstruction of the erythemally-weighted UV doses for 1955-2004 has been performed for the Tartu-Tõravere Meteorological Station (58°16' N, 26°28' E, 70 m a.s.l.) site. The pyrheliometer-measured daily sum of direct irradiance on partly cloudy and clear days, and the pyranometer-measured daily sum of global irradiance on overcast days were used as the cloudiness influence related proxies. The TOMS ozone data have been used for detecting the daily deviations from the climatic value (averaged annual cycle). In 1998–2004, the biases between the measured and reconstructed daily doses in 55.5% of the cases were within ±10% and in 83.5% of the cases within ±20%, on average. In the summer half-year these amounts were 62% and 88%, respectively. In most years the results for longer intervals did not differ significantly, if no correction was made for the daily deviations of total ozone from its climatic value. The annual and summer half-yearly erythemal doses (contributing, on average, 89% of the annual value) agreed within ±2%, except for the years after major volcanic eruptions and one extremely fine weather year (2002). Using the daily relative sunshine duration as a proxy without detailed correction for atmospheric turbidity results in biases of 2–4% in the summer half-yearly dose in the years after major volcanic eruptions and a few other years of high atmospheric turbidity. The year-to-year variations of the summer half-yearly erythemal dose in 1955–2004 were found to be within 92–111% relative to their average value. Exclusion of eight extreme years reduces this range for the remaining to 95–105.5%. Due to the quasi-periodic alternation of wet and dry periods, the interval of cloudy summers 1976–1993 regularly manifests summer half-yearly erythemal dose values lower than the 1955–2004 average. Since 1996/1997 midwinters have been darker than on average.

Impact of Antarctic polar vortex occurrences on total ozone and UVB radiation at southern Argentinean and Antarctic stations during 1997–2003 period

The evolution of total ozone and surface UV radiation over some stations in the southern region of South America and in Antarctica in relationship with polar vortex occurrences is analyzed using Total Ozone Mapping Spectrometer total ozone measurements and local surface UV data for the 1997–2003 period. The data are classified as a function of the position of the stations with respect to the polar vortex using equivalent latitude at 550 K isentropic level. The study of vortex occurrences showed that Ushuaia station (54.9°S) was located ∼40% of the cases in the edge of the vortex and 5% inside the vortex core during the winter‐spring period. Concerning the Marambio (62.2°S) and Dumont d'Urville (66.4°S) stations, located on the shore of the Antarctic continent, the analysis shows a zonal asymmetry with respect to the center of the vortex. Marambio is located around 60% of the time inside the vortex, while Dumont d'Urville is predominantly at the edge of or outside the vortex. The evolution of the equivalent latitude of the stations in the anomalous 2002 winter presents a different behavior with respect to other years in the 1997–2003 period. The persistence of the vortex core above the stations is in average 1.8 days over Ushuaia and 7.1 days over Marambio in October during the 1997–2003 period with corresponding mean total ozone columns of 208.2 and 181.4 Dobson units, respectively. When the stations are inside the vortex, the total ozone columns are generally larger at Ushuaia than at Marambio in October during the 1997–2003 period. Finally, the impact of ozone‐depleted air mass occurrences on ultraviolet radiation is evaluated by relating total ozone and UV erythemal dose measured at the stations. Twofold or threefold UV dose increases were reached in the 55°–65° southern latitude region during vortex overpasses, reaching maximum UV dose around 5 kJ/m2. The average increase of UV dose could be computed at the stations considered in the study when the measurement sampling and the number of vortex occurrences was sufficient. An average increase of 67.6% of the erythemal UV dose was found in October at Ushuaia over the years 1997, 1998, and 2000. This value is strongly weighted by vortex occurrences over the station in 2000. At Marambio an average UV increase of 47.4% was found over the years 1999 and 2000. Midlatitude stations like Comodoro Rivadavia (45.8°S) are generally little affected by vortex intrusions. Nevertheless, the maximum UV dose can increase by more than 50% when the vortex passes over the station.

Erythemal UV at Davos (Switzerland), 1926–2003, estimated using total ozone, sunshine duration, and snow depth

A method previously developed for reconstructing daily erythemal UV doses at Sodankylä, northern Finland, was adjusted to the local conditions at Davos, Switzerland, and used for estimating the erythemal UV doses there over the period 1926–2003. The method uses total ozone, sunshine duration, and snow depth as input, and is based on the empirical relationship between relative sunshine duration and relative UV doses. In order to examine how the method behaves in different environments, the relationships found for Davos and Sodankylä were compared. This revealed that the surface albedo and the cloud climate have a comparable influence on the relationship found. Although the method is fairly simple, it accounts for the most important factors affecting the amount of UV radiation reaching the Earth's surface. A comparison between estimated UV doses and the corresponding observations with a broadband biometer at Davos demonstrated the good performance of the method. The correlation coefficient for daily values varies between 0.95 and 0.98 depending on time of year, and the corresponding root mean square error is typically of the order of 20%. The monthly mean values show considerably less scatter around the regression line with a root mean square error of 4%. The time series of estimated UV shows that the UV level at Davos has varied considerably throughout the period of this study, with high values in the middle of the 1940s, in the early 1960s, and in the 1990s. Variations in the estimated UV doses prior to 1980, e.g., a steady decrease from the early 1960s to the late 1970s, were found to be caused primarily by changes in sunshine duration. Since 1980, on the other hand, there has been a distinct increase in the UV level caused mainly by the diminution of total ozone. This increase is most clearly seen during winter and spring, while the decrease from the early 1960s to the late 1970s is most pronounced during summer.