Vitamin D is important for bone health, is linked to many other health benefits including protect... more Vitamin D is important for bone health, is linked to many other health benefits including protection against a range of malignancies and autoimmune disorders, and is known to modulate many biological responses including cell differentiation. It is therefore important to evaluate the vitamin D status of the general population in the context of recommended target levels and public health advice on vitamin D acquisition. The accepted best indicator of vitamin D status is the circulating level of 25-hydroxyvitamin D (25OHD). The Institute of Medicine for the USA and Canada advises a target 25OHD level of ≥20 ng/ml (50 nmol/L) based on parameters of bone health, and recommends oral intake of ≥600 IU daily. The target is currently under review in the UK, where most adults are not advised of any oral vitamin D requirement as adequate intake has been assumed to occur from cutaneous synthesis following regular brief UV exposures. Through a series of intervention studies, we demonstrated that...
Public health guidelines in the UK assume that from school age to retirement (ages 4 - 64 years) ... more Public health guidelines in the UK assume that from school age to retirement (ages 4 - 64 years) all vitamin D requirements are met by synthesis of the vitamin in skin after exposure to solar (UV) radiation. The exceptions are "at risk" groups including pregnant and lactating women, and those over 65, for whom 10 ug/day (400 iu) is recommended. Under the age of 4, during rapid growth and with acknowledgement of the vulnerability of delicate skin to sun exposure, and intake of 8.5, falling to 7 ug/day is recommended. These intakes, defined in 1991 and re-assessed and unchanged in 1998, are predicated on avoiding rickets and maintaining a healthy skeleton, with 25 nmol/l (10 ng/ml) of circulating 25-hydroxyvitamin D defined as the lower limit of acceptable vitamin D status. They do not address other potential benefits of vitamin D. In a series of studies in the Greater Manchester (UK) area we have investigated both the dietary and the sun-induced skin synthesis contributions...
Spectrally resolved high quality actinic flux measurements between 290 nm and 500 nm have been pe... more Spectrally resolved high quality actinic flux measurements between 290 nm and 500 nm have been performed in complex Alpine terrain under clear sky conditions. A three-dimensional Monte Carlo radiative transfer model was adapted for actinic flux calculations in mountainous terrain. This model is used to study the impact of topography and surface albedo on surface spectral actinic flux and no2- and o3-photolysis rates. This approach leads to surface maps of actinic flux and photolysis rates. The typical high spatial variability due to altitude, snow cover and shading affects is very well reproduced in the model. By running the model in three modes (realistic, without topography, with albedo zero) one gets a good estimation of the impact of topography and surface albedo.
A detailed map of the available UV across the UK from 2003 to 2012 is provided. A suite of data d... more A detailed map of the available UV across the UK from 2003 to 2012 is provided. A suite of data derived from climatologies and satellite observations are used to calculate spectral UV irradiance and related weighted doses (erythema, DNA damage, vitamin D). The result is a well-validated tool that has two advantages: (i) the output is simulated spectral UV irradiance that can be weighted with any action spectrum for use in any research studies that require ambient UV data, (ii) reliance on instruments with planned operational lives of at least several years that ensures data and method homogeneity for extension to future studies. The model-derived doses are satisfactory validated against spectral ground-based measurements at two sites. According to the calculated climatology, the southern part of the UK receives 1.5-2 times more UV than the north during spring, summer and autumn. During wintertime, the UV doses in the far north are an order of magnitude lower than southern values. Even for the same latitude, regional variations of cloudiness result in doses at coastal sites being up to 25% higher than inland areas.
Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific commun... more Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific community has shown an increasing interest in UV-B radiation. Nowadays, ground-based high quality measurements of spectrally resolved UV-radiation are available. On the other hand, 1-D- and 3-D models have been developed, that describe the radiative transfer through the atmosphere physically very accurately. Another approach for determining the UV-irradiance at the surface of the earth is the use of satellite-based reflectance measurements as input for retrieval algorithms. At the moment, the research focuses on the impact of clouds on UV-radiation, but the impact of mountains on UV-radiation, especially in combination with high surface albedo due to snowcover, is also very strong and detailed comparisons between measurements and modelling are lacking. Therefore, three measurement campaigns had been conducted in alpine areas of Austria (Innsbruck and Hoher Sonnblick). The goal was to investiga...
Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific commun... more Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific community has shown an increasing interest in UV radiation. However for photochemical reactions and various biological processes actinic flux is more important. Therefore, three measurement campaigns had been conducted in alpine areas of Austria (Innsbruck and Hoher Sonnblick). The goal was to investigate the impact of alpine terrain in combination with snow cover on spectral actinic flux under clear sky conditions. This contribution uses the ground-based UV actinic flux measurements to evaluate two different calculation methods. The modified (with topography) 3-D radiative transfer model GRIMALDI was used to calculate the distribution of actinic flux at the ground for selected clear sky situations. To estimate the impact of 3-D effects on actinic flux, the measurement results are also compared with the output of 1-D-model (SDISORT) runs. Apart from border problems due to periodic boundary con...
Journal of the European Academy of Dermatology and Venereology, 2014
Background Sun exposure has positive and negative effects on health, yet little is known about th... more Background Sun exposure has positive and negative effects on health, yet little is known about the sun-exposure behaviour of UK adolescents, including those more prone or less prone to sunburn.
Vitamin D insufficiency and deficiency remain prevalent at northerly latitude, particularly in in... more Vitamin D insufficiency and deficiency remain prevalent at northerly latitude, particularly in individuals of South Asian ethnicity. Health agencies advise that low vitamin D status can be avoided through short casual summer sunlight exposures but this advice is geared towards white skinned people. A UV exposure regime simulating this can produce vitamin D sufficiency (25[OH]D ≥20 ng/mL) in 90% of UK white Caucasians but none of the S. Asians attained this level. As skin cancer risk is low in S. Asians, we examined whether higher UV exposure levels could produce vitamin D sufficiency and avoid deficiency (25[OH]D <10 ng/mL).
Public health policy advises limiting summer sunlight exposure, but provides no specific advice f... more Public health policy advises limiting summer sunlight exposure, but provides no specific advice for darker-skinned people. This study assessed the relative vitamin D gain on following UK sunlight exposure recommendations in White Caucasians and South Asians. During wintertime (negligible ambient UVB), 86 volunteers (n=70 skin-type II, 16 skin-type V), 20-60y, Manchester, UK, received a simulated summer's sunlight exposures, comprising 1.3SED, 3 x weekly for 6wks, wearing T-shirt and UV-opaque shorts. Circulating 25(OH)D was evaluated by HPLC (n=60 x II, 10 x V). A 10 x 10 cm 2 area of one buttock was left exposed (n=10 x II, 6 x V) and underwent spectrophotometric measurements. At course end, exposed and unexposed skin received an acute 2 x MED challenge, with 24 h measurements. Vitamin D status improved post-course, with significant difference in 25(OH)D gain between types II (mean 10.2, SD 7.5ng/ml) and V (4.6, 1.9), p<0.05. Baseline L* (white-black differentiation) differed between groups, reflecting higher pigmentation of V, p<0.01. The exposures darkened the skin, decreasing L* by 6.2(5.3), p<0.001, with 6% and 24% reduction in II and V respectively, and with strong negative correlation between L* decrease and 25(OH)D gain (R 2 = 0.94, 0.92; p<0.001). The simulated summer conveyed photoprotection, UV-treated skin demonstrating lower A* values (erythema) than UV protected skin after challenge with 2 x MED, p<0.05, with 14% erythema protection in II and 50% in V. Thus, the same summer exposure conditions cause approximately half the 25(OH)D gain in darker than fair skin-types, with greater pigmentation gain contributing to this. More specific advice on sunlight exposure may be required for people of skin type V living at higher latitude.
The UK's current nutritional guidelines assume that from school to retirement, vitamin D requirem... more The UK's current nutritional guidelines assume that from school to retirement, vitamin D requirements are met by skin exposure to UVB in sunlight. However, it is well documented that at latitudes such as the UK, the sunlight in the winter can be insufficient to synthesize appreciable vitamin D levels. We are funded by the UK Department of Health to provide data to inform new national guidance on vitamin D acquisition. In this study we use a well-established radiative transfer model to map the available UVB across the UK during the last 10 years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). A suite of data (aerosol optical properties, surface reflectivity, cloud optical depth and coverage, total ozone column and digital elevation) derived from satellite estimates are used as model inputs to calculate the spectral UV irradiance and the vitamin D dose for different time periods. The model-derived vitamin D doses are validated against spectral irradiance measurements at Reading (51.44N, 0.94E) and Manchester (53.47N, 2.23E). Results from more than 2500 days at each site reveal that the modeled dose is overestimated by 5% while the overall agreement is satisfactory (R 2 >0.9) since the ground-based measurements are not always representative of a typical satellite measurement pixel. On a monthly basis, the overall agreement is significantly improved (bias <2%, R 2 =0.99). The model results will be combined with controlled exposure studies that determined how much vitamin D is synthesized per dose of UVB in adults with different skin types. This enables an estimate of the vitamin D effective exposure available across the UK for different skin types under realistic climatological conditions. Further studies provide for a range of actual exposure patterns within the theoretical availability.
Ultraviolet Ground- and Space-based Measurements, Models, and Effects II, 2003
Actinic flux (the radiation incident on the surface of a small sphere) is the measure of radiatio... more Actinic flux (the radiation incident on the surface of a small sphere) is the measure of radiation required for atmospheric chemistry. The photolysis rate for a given species is the product of its absorption cross-section, quantum yield and the actinic flux, integrated over all relevant wavelengths. Despite their importance, actinic flux and photolysis rate data are not routinely available since radiation monitoring sites usually report irradiances (radiation on a flat, horizontal surface). Using data from Reading (UK) we show that spectral UV actinic fluxes can be derived from spectral irradiance measurements with a scanning spectroradiometer (Bentham DTM300) to within an uncertainty of 20% full range, or 15% if sky conditions are known. Any photolysis rate dependent on these wavelengths can then be calculated from the actinic flux data. The disadvantage of spectroradiometers is their scan time of several minutes. The GUV-541 multi-band radiometer measures across 5 narrow UV channels simultaneously and samples at a rate of 2-3Hz. Using a semi-empirical formula, this multi-band irradiance data can be converted into photolysis rates for J(O3) and J(NO2). The GUV derived photolysis rates were within 20% of those calculated from spectral actinic fluxes under all conditions tested. This compares well with other methods of measuring photolysis rates.
We present a unique case study of the solar global irradiance in a highly heterogeneous albedo en... more We present a unique case study of the solar global irradiance in a highly heterogeneous albedo environment at the arctic coast. Diodearray spectroradiometers were deployed at three sites around Ny Ålesund, Svalbard, and spectral irradiances were simultaneously measured under clear sky conditions during a 24 h period. The 3-D 5 radiative transfer model MYSTIC is applied to simulate the measurements in various model scenarios. First, we model the effective albedos of ocean and snow and consequently around each measurement site. The effective albedos at 340 nm increase from 0.57 to 0.75, from the coastal site in the west towards the site 20 km east, away from the coast. The observed ratios of the global irradiance indicate a 15 % higher 10 average irradiance at east relative to west at 340 nm due to the higher albedo. The comparison to our model scenarios suggest a snow albedo of > 0.9 and confirm the observation that drift ice has moved into the Fjord during the day. The local time shift between the locations causes a hysteresis-like behavior of these east-west ratios with solar zenith angle (SZA). The observed hysteresis, however, is larger and, at 340 nm, 15 can be explained by the drift ice. At 500 nm, a plausible explanation is a detector tilt of about 1 • . The ratios between afternoon and morning irradiances at the same SZA are investigated, which confirm the above conclusions. At the coastal site, the measured irradiance is significantly higher in the afternoon than in the morning. Besides the effect of changing drift ice and detector tilt, the small variations of the aerosol optical depth 20 have to be considered also at the other stations to reduce the discrepancies between model and observations. Remaining discrepancies are possibly due to high thin clouds.
Remote Sensing of Clouds and the Atmosphere XI, 2006
abstract On 29 March 2006, a total eclipse of the Sun was visible on the Greek island Kastelorizo... more abstract On 29 March 2006, a total eclipse of the Sun was visible on the Greek island Kastelorizo (36.150 N, 29.596 E). An extended set of instruments was installed in order to measure the variability of different components of the radiation field during the eclipse. Seven spectroradiometers (two scanning double monochromators measuring especially in the UV range, 4 photo diode array instruments and one CCD-spectrograph for the UV and visible wavelength range) performed measurements during 28 and 29 March. A narrow ...
There are a range of UV models available, but one needs significant pre-existing knowledge and ex... more There are a range of UV models available, but one needs significant pre-existing knowledge and experience in order to be able to use them. In this article a comparatively simple Web-based model developed for the SoDa (Integration and Exploitation of Networked Solar Radiation Databases for Environment Monitoring) project is presented. This is a clear-sky model with modifications for cloud effects. To determine if the model produces realistic UV data the output is compared with 1 year sets of hourly measurements at sites in the United Kingdom and Thailand. The accuracy of the output depends on the input, but reasonable results were obtained with the use of the default database inputs and improved when pyranometer instead of modeled data provided the global radiation input needed to estimate the UV. The average modeled values of UV for the UK site were found to be within 10% of measurements. For the tropical sites in Thailand the average modeled values were within 1120% of measurements...
Journal of Photochemistry and Photobiology B: Biology, 2014
The objective of the present study was to identify external, intrinsic or behavioural factors tha... more The objective of the present study was to identify external, intrinsic or behavioural factors that significantly influenced serum 25-hydroxyvitamin D (25(OH)D) concentrations in a German survey. Data from 3061 participants in the Cooperative Health Research in the Region of Augsburg, Germany (KORA) F4 survey were used to relate potential determinants to measured mean serum 25(OH)D concentrations using multivariable regression models. The factors significantly associated with hypovitaminosis D (defined as 25(OH)D&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;25 nmolL(-1)) were season (winter, spring and autumn), urban environment and high body mass index. In contrast, times spent in sunny regions, hours per day spent outdoors in the summer as well as additional oral intake were associated with higher 25(OH)D concentrations. These results suggest that mainly ambient UV exposure but also individual behaviour are the most important determinants for personal 25(OH)D concentrations. The analyses further showed that in winter 43% of subjects were vitamin D deficient and 42% insufficient. Even in summer over half the population has insufficient vitamin D status with 8% deficient and 47% insufficient. Therefore measures to mitigate widespread vitamin D insufficiency such as regular short-term sun exposure and/or improved dietary intake/supplementation recommendations by public health bodies need to be considered.
The vast majority of radiation measurements, including UV, refer to the radiation incident on a f... more The vast majority of radiation measurements, including UV, refer to the radiation incident on a flat horizontal plate. However, this may not be the most appropriate way to specify radiation for bodies affected by UV, since they are rarely flat or horizontal. In particular the target molecules involved in atmospheric chemistry are approximately spherical and the actinic flux would be a better measure of the incident radiation. The ADMIRA project is addressing the issue of converting spectral UV irradiances to spectral actinic fluxes that can then be weighted with any required cross-section or action spectrum to give photolysis rates or biologically effective radiation incident on a sphere. The success with which this conversion can be made will depend on the prevailing atmospheric conditions and the knowledge of such at the time the irradiance measurements were made. Several different approaches to the conversion are being assessed, together with their associated uncertainties. These...
Vitamin D is important for bone health, is linked to many other health benefits including protect... more Vitamin D is important for bone health, is linked to many other health benefits including protection against a range of malignancies and autoimmune disorders, and is known to modulate many biological responses including cell differentiation. It is therefore important to evaluate the vitamin D status of the general population in the context of recommended target levels and public health advice on vitamin D acquisition. The accepted best indicator of vitamin D status is the circulating level of 25-hydroxyvitamin D (25OHD). The Institute of Medicine for the USA and Canada advises a target 25OHD level of ≥20 ng/ml (50 nmol/L) based on parameters of bone health, and recommends oral intake of ≥600 IU daily. The target is currently under review in the UK, where most adults are not advised of any oral vitamin D requirement as adequate intake has been assumed to occur from cutaneous synthesis following regular brief UV exposures. Through a series of intervention studies, we demonstrated that...
Public health guidelines in the UK assume that from school age to retirement (ages 4 - 64 years) ... more Public health guidelines in the UK assume that from school age to retirement (ages 4 - 64 years) all vitamin D requirements are met by synthesis of the vitamin in skin after exposure to solar (UV) radiation. The exceptions are "at risk" groups including pregnant and lactating women, and those over 65, for whom 10 ug/day (400 iu) is recommended. Under the age of 4, during rapid growth and with acknowledgement of the vulnerability of delicate skin to sun exposure, and intake of 8.5, falling to 7 ug/day is recommended. These intakes, defined in 1991 and re-assessed and unchanged in 1998, are predicated on avoiding rickets and maintaining a healthy skeleton, with 25 nmol/l (10 ng/ml) of circulating 25-hydroxyvitamin D defined as the lower limit of acceptable vitamin D status. They do not address other potential benefits of vitamin D. In a series of studies in the Greater Manchester (UK) area we have investigated both the dietary and the sun-induced skin synthesis contributions...
Spectrally resolved high quality actinic flux measurements between 290 nm and 500 nm have been pe... more Spectrally resolved high quality actinic flux measurements between 290 nm and 500 nm have been performed in complex Alpine terrain under clear sky conditions. A three-dimensional Monte Carlo radiative transfer model was adapted for actinic flux calculations in mountainous terrain. This model is used to study the impact of topography and surface albedo on surface spectral actinic flux and no2- and o3-photolysis rates. This approach leads to surface maps of actinic flux and photolysis rates. The typical high spatial variability due to altitude, snow cover and shading affects is very well reproduced in the model. By running the model in three modes (realistic, without topography, with albedo zero) one gets a good estimation of the impact of topography and surface albedo.
A detailed map of the available UV across the UK from 2003 to 2012 is provided. A suite of data d... more A detailed map of the available UV across the UK from 2003 to 2012 is provided. A suite of data derived from climatologies and satellite observations are used to calculate spectral UV irradiance and related weighted doses (erythema, DNA damage, vitamin D). The result is a well-validated tool that has two advantages: (i) the output is simulated spectral UV irradiance that can be weighted with any action spectrum for use in any research studies that require ambient UV data, (ii) reliance on instruments with planned operational lives of at least several years that ensures data and method homogeneity for extension to future studies. The model-derived doses are satisfactory validated against spectral ground-based measurements at two sites. According to the calculated climatology, the southern part of the UK receives 1.5-2 times more UV than the north during spring, summer and autumn. During wintertime, the UV doses in the far north are an order of magnitude lower than southern values. Even for the same latitude, regional variations of cloudiness result in doses at coastal sites being up to 25% higher than inland areas.
Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific commun... more Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific community has shown an increasing interest in UV-B radiation. Nowadays, ground-based high quality measurements of spectrally resolved UV-radiation are available. On the other hand, 1-D- and 3-D models have been developed, that describe the radiative transfer through the atmosphere physically very accurately. Another approach for determining the UV-irradiance at the surface of the earth is the use of satellite-based reflectance measurements as input for retrieval algorithms. At the moment, the research focuses on the impact of clouds on UV-radiation, but the impact of mountains on UV-radiation, especially in combination with high surface albedo due to snowcover, is also very strong and detailed comparisons between measurements and modelling are lacking. Therefore, three measurement campaigns had been conducted in alpine areas of Austria (Innsbruck and Hoher Sonnblick). The goal was to investiga...
Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific commun... more Since the discovery of anthropogenic ozone depletion more than 30 year ago, the scientific community has shown an increasing interest in UV radiation. However for photochemical reactions and various biological processes actinic flux is more important. Therefore, three measurement campaigns had been conducted in alpine areas of Austria (Innsbruck and Hoher Sonnblick). The goal was to investigate the impact of alpine terrain in combination with snow cover on spectral actinic flux under clear sky conditions. This contribution uses the ground-based UV actinic flux measurements to evaluate two different calculation methods. The modified (with topography) 3-D radiative transfer model GRIMALDI was used to calculate the distribution of actinic flux at the ground for selected clear sky situations. To estimate the impact of 3-D effects on actinic flux, the measurement results are also compared with the output of 1-D-model (SDISORT) runs. Apart from border problems due to periodic boundary con...
Journal of the European Academy of Dermatology and Venereology, 2014
Background Sun exposure has positive and negative effects on health, yet little is known about th... more Background Sun exposure has positive and negative effects on health, yet little is known about the sun-exposure behaviour of UK adolescents, including those more prone or less prone to sunburn.
Vitamin D insufficiency and deficiency remain prevalent at northerly latitude, particularly in in... more Vitamin D insufficiency and deficiency remain prevalent at northerly latitude, particularly in individuals of South Asian ethnicity. Health agencies advise that low vitamin D status can be avoided through short casual summer sunlight exposures but this advice is geared towards white skinned people. A UV exposure regime simulating this can produce vitamin D sufficiency (25[OH]D ≥20 ng/mL) in 90% of UK white Caucasians but none of the S. Asians attained this level. As skin cancer risk is low in S. Asians, we examined whether higher UV exposure levels could produce vitamin D sufficiency and avoid deficiency (25[OH]D <10 ng/mL).
Public health policy advises limiting summer sunlight exposure, but provides no specific advice f... more Public health policy advises limiting summer sunlight exposure, but provides no specific advice for darker-skinned people. This study assessed the relative vitamin D gain on following UK sunlight exposure recommendations in White Caucasians and South Asians. During wintertime (negligible ambient UVB), 86 volunteers (n=70 skin-type II, 16 skin-type V), 20-60y, Manchester, UK, received a simulated summer's sunlight exposures, comprising 1.3SED, 3 x weekly for 6wks, wearing T-shirt and UV-opaque shorts. Circulating 25(OH)D was evaluated by HPLC (n=60 x II, 10 x V). A 10 x 10 cm 2 area of one buttock was left exposed (n=10 x II, 6 x V) and underwent spectrophotometric measurements. At course end, exposed and unexposed skin received an acute 2 x MED challenge, with 24 h measurements. Vitamin D status improved post-course, with significant difference in 25(OH)D gain between types II (mean 10.2, SD 7.5ng/ml) and V (4.6, 1.9), p<0.05. Baseline L* (white-black differentiation) differed between groups, reflecting higher pigmentation of V, p<0.01. The exposures darkened the skin, decreasing L* by 6.2(5.3), p<0.001, with 6% and 24% reduction in II and V respectively, and with strong negative correlation between L* decrease and 25(OH)D gain (R 2 = 0.94, 0.92; p<0.001). The simulated summer conveyed photoprotection, UV-treated skin demonstrating lower A* values (erythema) than UV protected skin after challenge with 2 x MED, p<0.05, with 14% erythema protection in II and 50% in V. Thus, the same summer exposure conditions cause approximately half the 25(OH)D gain in darker than fair skin-types, with greater pigmentation gain contributing to this. More specific advice on sunlight exposure may be required for people of skin type V living at higher latitude.
The UK's current nutritional guidelines assume that from school to retirement, vitamin D requirem... more The UK's current nutritional guidelines assume that from school to retirement, vitamin D requirements are met by skin exposure to UVB in sunlight. However, it is well documented that at latitudes such as the UK, the sunlight in the winter can be insufficient to synthesize appreciable vitamin D levels. We are funded by the UK Department of Health to provide data to inform new national guidance on vitamin D acquisition. In this study we use a well-established radiative transfer model to map the available UVB across the UK during the last 10 years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). A suite of data (aerosol optical properties, surface reflectivity, cloud optical depth and coverage, total ozone column and digital elevation) derived from satellite estimates are used as model inputs to calculate the spectral UV irradiance and the vitamin D dose for different time periods. The model-derived vitamin D doses are validated against spectral irradiance measurements at Reading (51.44N, 0.94E) and Manchester (53.47N, 2.23E). Results from more than 2500 days at each site reveal that the modeled dose is overestimated by 5% while the overall agreement is satisfactory (R 2 >0.9) since the ground-based measurements are not always representative of a typical satellite measurement pixel. On a monthly basis, the overall agreement is significantly improved (bias <2%, R 2 =0.99). The model results will be combined with controlled exposure studies that determined how much vitamin D is synthesized per dose of UVB in adults with different skin types. This enables an estimate of the vitamin D effective exposure available across the UK for different skin types under realistic climatological conditions. Further studies provide for a range of actual exposure patterns within the theoretical availability.
Ultraviolet Ground- and Space-based Measurements, Models, and Effects II, 2003
Actinic flux (the radiation incident on the surface of a small sphere) is the measure of radiatio... more Actinic flux (the radiation incident on the surface of a small sphere) is the measure of radiation required for atmospheric chemistry. The photolysis rate for a given species is the product of its absorption cross-section, quantum yield and the actinic flux, integrated over all relevant wavelengths. Despite their importance, actinic flux and photolysis rate data are not routinely available since radiation monitoring sites usually report irradiances (radiation on a flat, horizontal surface). Using data from Reading (UK) we show that spectral UV actinic fluxes can be derived from spectral irradiance measurements with a scanning spectroradiometer (Bentham DTM300) to within an uncertainty of 20% full range, or 15% if sky conditions are known. Any photolysis rate dependent on these wavelengths can then be calculated from the actinic flux data. The disadvantage of spectroradiometers is their scan time of several minutes. The GUV-541 multi-band radiometer measures across 5 narrow UV channels simultaneously and samples at a rate of 2-3Hz. Using a semi-empirical formula, this multi-band irradiance data can be converted into photolysis rates for J(O3) and J(NO2). The GUV derived photolysis rates were within 20% of those calculated from spectral actinic fluxes under all conditions tested. This compares well with other methods of measuring photolysis rates.
We present a unique case study of the solar global irradiance in a highly heterogeneous albedo en... more We present a unique case study of the solar global irradiance in a highly heterogeneous albedo environment at the arctic coast. Diodearray spectroradiometers were deployed at three sites around Ny Ålesund, Svalbard, and spectral irradiances were simultaneously measured under clear sky conditions during a 24 h period. The 3-D 5 radiative transfer model MYSTIC is applied to simulate the measurements in various model scenarios. First, we model the effective albedos of ocean and snow and consequently around each measurement site. The effective albedos at 340 nm increase from 0.57 to 0.75, from the coastal site in the west towards the site 20 km east, away from the coast. The observed ratios of the global irradiance indicate a 15 % higher 10 average irradiance at east relative to west at 340 nm due to the higher albedo. The comparison to our model scenarios suggest a snow albedo of > 0.9 and confirm the observation that drift ice has moved into the Fjord during the day. The local time shift between the locations causes a hysteresis-like behavior of these east-west ratios with solar zenith angle (SZA). The observed hysteresis, however, is larger and, at 340 nm, 15 can be explained by the drift ice. At 500 nm, a plausible explanation is a detector tilt of about 1 • . The ratios between afternoon and morning irradiances at the same SZA are investigated, which confirm the above conclusions. At the coastal site, the measured irradiance is significantly higher in the afternoon than in the morning. Besides the effect of changing drift ice and detector tilt, the small variations of the aerosol optical depth 20 have to be considered also at the other stations to reduce the discrepancies between model and observations. Remaining discrepancies are possibly due to high thin clouds.
Remote Sensing of Clouds and the Atmosphere XI, 2006
abstract On 29 March 2006, a total eclipse of the Sun was visible on the Greek island Kastelorizo... more abstract On 29 March 2006, a total eclipse of the Sun was visible on the Greek island Kastelorizo (36.150 N, 29.596 E). An extended set of instruments was installed in order to measure the variability of different components of the radiation field during the eclipse. Seven spectroradiometers (two scanning double monochromators measuring especially in the UV range, 4 photo diode array instruments and one CCD-spectrograph for the UV and visible wavelength range) performed measurements during 28 and 29 March. A narrow ...
There are a range of UV models available, but one needs significant pre-existing knowledge and ex... more There are a range of UV models available, but one needs significant pre-existing knowledge and experience in order to be able to use them. In this article a comparatively simple Web-based model developed for the SoDa (Integration and Exploitation of Networked Solar Radiation Databases for Environment Monitoring) project is presented. This is a clear-sky model with modifications for cloud effects. To determine if the model produces realistic UV data the output is compared with 1 year sets of hourly measurements at sites in the United Kingdom and Thailand. The accuracy of the output depends on the input, but reasonable results were obtained with the use of the default database inputs and improved when pyranometer instead of modeled data provided the global radiation input needed to estimate the UV. The average modeled values of UV for the UK site were found to be within 10% of measurements. For the tropical sites in Thailand the average modeled values were within 1120% of measurements...
Journal of Photochemistry and Photobiology B: Biology, 2014
The objective of the present study was to identify external, intrinsic or behavioural factors tha... more The objective of the present study was to identify external, intrinsic or behavioural factors that significantly influenced serum 25-hydroxyvitamin D (25(OH)D) concentrations in a German survey. Data from 3061 participants in the Cooperative Health Research in the Region of Augsburg, Germany (KORA) F4 survey were used to relate potential determinants to measured mean serum 25(OH)D concentrations using multivariable regression models. The factors significantly associated with hypovitaminosis D (defined as 25(OH)D&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;25 nmolL(-1)) were season (winter, spring and autumn), urban environment and high body mass index. In contrast, times spent in sunny regions, hours per day spent outdoors in the summer as well as additional oral intake were associated with higher 25(OH)D concentrations. These results suggest that mainly ambient UV exposure but also individual behaviour are the most important determinants for personal 25(OH)D concentrations. The analyses further showed that in winter 43% of subjects were vitamin D deficient and 42% insufficient. Even in summer over half the population has insufficient vitamin D status with 8% deficient and 47% insufficient. Therefore measures to mitigate widespread vitamin D insufficiency such as regular short-term sun exposure and/or improved dietary intake/supplementation recommendations by public health bodies need to be considered.
The vast majority of radiation measurements, including UV, refer to the radiation incident on a f... more The vast majority of radiation measurements, including UV, refer to the radiation incident on a flat horizontal plate. However, this may not be the most appropriate way to specify radiation for bodies affected by UV, since they are rarely flat or horizontal. In particular the target molecules involved in atmospheric chemistry are approximately spherical and the actinic flux would be a better measure of the incident radiation. The ADMIRA project is addressing the issue of converting spectral UV irradiances to spectral actinic fluxes that can then be weighted with any required cross-section or action spectrum to give photolysis rates or biologically effective radiation incident on a sphere. The success with which this conversion can be made will depend on the prevailing atmospheric conditions and the knowledge of such at the time the irradiance measurements were made. Several different approaches to the conversion are being assessed, together with their associated uncertainties. These...
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