The Austrian UVA‐Network
Alois W. Schmalwieser Barbara Klotz Michael Schwarzmann Dietmar J. Baumgartner Josef Schreder Günther Schauberger Mario Blumthaler
First published: 24 April 2019 https://doi.org/10.1111/php.13111
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Abstract
The ultraviolet‐A (UVA) part of the solar spectrum at the Earth's surface is an essential environmental factor but continuous long‐time monitoring of UVA radiation is rarely done. In Austria, three existing stations of the UV monitoring network have been upgraded with UVA broadband instruments. At each station, one instrument measures global UVA irradiance and—in parallel—a second instrument measures diffuse irradiance. Recent and past measurements are available via a web page. This paper describes the used instruments, calibration and quality assurance and control procedures. Global and diffuse UVA measurements during a period of up to 5 years are presented. Data indicate clear annual courses and an increase of UVA with altitude by 8–9% per 1000 m. In the first half of the year, UVA radiation is higher than in the second half, due to less cloudiness. In Vienna (153 m asl), the mean daily global UVA radiant exposure in summer is almost as high as at Mt. Gerlitzen (1540 m asl), equalizing the altitude effect, due to less cloudiness. However, in winter, the UVA radiant exposure at Mt. Gerlitzen is double as high, as in Vienna.
Introduction
The ultraviolet‐A (UVA) range (315–400 nm) of the solar spectrum is rarely a topic of continuous monitoring, although UVA is highly important for plants, animals and humans. More common are measurements at certain wavelengths in the UVA range to characterize atmospheric conditions by spectroradiometers (e.g. 1) or narrowband filter radiometers (e.g. 2) and of course most common are measurements of the UV index (e.g. 3). A possible reason for the almost complete lack of UVA monitoring might be that the effects on livings from UVA radiation appear less dramatic than those from the ultraviolet‐B (UVB) radiation (e.g. erythema or skin cancer). However, the photobiological and ecological impact of the UVA radiation is as wide as of the UVB radiation.
The visual sense of many animal species is sensitive to UVA radiation, due to an UV sensitive photoreceptor and an UV transmissive lens. Visual perception in the UVA range is long known in invertebrates 4, 5 and fish 6, 7, was discovered in birds and reptiles in the 1980s 8, 9 and has in the meanwhile been even recognized in some mammalian species (e.g. ferret, reindeer 10). A change of UVA radiation results in a change in the color perception of these animals 11. For farm animals and animals that are kept indoors (e.g. zoo, aviary, terrarium), the availability and quality of UVA radiation are important to ensure their well‐being. However, the data available on natural levels of UVA radiation are very limited.
In respect to human and mammalian skin, UVA radiation initiates pigmentation (e.g. 12), which protects the skin from the sun to a certain extent 13, but UVA radiation also contributes effectively to skin aging and wrinkling 14, which may be cosmetically undesirable or even become pathogenic.
Already repeated low exposure to UVA radiation leads to measureable alterations 15, 16.
Inside the skin, UVA radiation affects the lipids of cells, which results in a decreased cell metabolism. Furthermore, UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which can damage DNA. Additionally, UVA radiation is the main trigger for photosensitivity reactions (e.g. phototoxicity and photoallergy 17). As UVA radiation transmits deeper into the skin (dermis) and into the eye (e.g. 18) than UVB radiation, a significantly larger amount of cells, as well as other tissues (e.g. macular degeneration 19), can be stroked by photons.
UVA radiation also penetrates more deeply into other mediums like water, plant crops or clothes. For considering UV exposure in everyday life, it has also to be taken into account that glasses (e.g. 20) of windows and windows of vehicles 21 are partially transmissive for UVA radiation. Due to this, people are exposed to UVA radiation, while shielded from UVB radiation.
The amount of UVA radiation reaching the earth's surface is magnitudes greater than that of UVB radiation (e.g. 22). Therefore, UVA radiation makes a significant contribution to photobiological effects (like nonmelanoma skin cancer, cataract 23 or immunosuppression 24), even if its effectivity is much lower than that of the UVB radiation.
An important vital effect initiated by UVA radiation is photorepair of DNA damage in plants (e.g. 25), but also in microorganisms (e.g. 26). Therefore, the ratio between the damaging UVB radiation and repairing UVA radiation becomes important. In the case of microorganism, the ratio between photoinactivation and photorepair changes throughout the year (e.g. 27), which may lead to periods which favor the spreading of microorganisms and periods which restrain the spreading. This may result in a reduction or enhancement of airborne infection diseases. There are some hints that the ratio of solar UVB and UVA radiation may be responsible for the spread of influenza A during the winter 28.
Interest in solely measuring UVA radiation was aroused, as the application of UVA radiation became common in phototherapy of certain skin diseases like psoriasis. This happens in conjunction with photosensitizing substances like psoralen. Therefore, several studies were undertaken to investigate the intensity of natural solar UVA radiation for comparison with UVA radiation from artificial sources to avoid overexposure of patients (e.g. 29). Also, in some of the internationally recognized regions for heliotherapy (e.g. psoriasis, atopic dermatitis, vitiligo) like the Dead Sea basin (e.g. 30) or Cyprus (e.g. 31), UVA radiation is a matter of interest.
Another application where UVA radiation measurements are necessary is SODIS (solar water disinfection) 32. SODIS is a low‐cost alternative, especially in southern regions, to the disinfection by mercury‐vapor‐pressure lamps which emit in the more effective UVC and UVB range. Here, irradiance measurements are used to calculate the gained fluence (e.g. 33), respectively, the duration of irradiation needed to ensure disinfection.
A variety of studies focusing on the nature of environmental solar UVA radiation and its influencing factors have been carried out in the past.
It was shown that the spatial variation of sky radiance in the UVA range (e.g. 34) can take a factor of 10. Generally, clouds and aerosols reduce UVA radiation (e.g. 35, 36). However, under broken cloud conditions, UVA radiation can be enhanced (e.g. 37), compared to clear sky. Albedo is another influencing factor (e.g. 38) that changes with time (e.g. snow cover). Global UVA radiation increases significantly with altitude (e.g. 39-42). Especially in alpine regions, there is a complex interaction between clouds, albedo and altitude (e.g. 43).
The ongoing global climate change does not affect the biosphere homogeneously. Changes occur on different spatial and temporal scales (e.g. seasonal change of cloud cover) and progress with different speeds. These also affect the amount of incoming UV radiation and its biological effectiveness (e.g. 44). Reliable long‐term monitoring is necessary in conjunction to a certain spatial resolution to make changes visible and evident.
In Austria, continuous online UV monitoring started in 1998 on behalf of the Austrian Ministry of Environment by establishing the Austrian UV index network 45. So‐called biometers have been utilized, which are broadband radiometers with erythema‐like spectral sensitivity (Model 501, Solar Light Inc., USA; 46). Locations of stations were selected by an objective method 47 in order to cover the whole country under special consideration of its geographical features, like the Alps. Today, the network consists of 13 stations and another 6 stations from neighboring countries participate in the online monitoring. These biometers mainly give information about the UVB range, due to their spectral response. So in a next step, the network was expanded by UVA broadband radiometers, which were placed aside the biometers at three stations. Today, at each of these stations, a UVA broadband radiometer measures global irradiance (sum of direct and diffuse radiation), while a second one is equipped with a shadow ring and only measures diffuse irradiance in parallel.
An important topic in monitoring is the quality of data and comparability. In this paper, we will introduce the applied methods for quality assurance and control including characteristics of instruments and calibration. Measurements and an analysis of global and diffuse UVA irradiance and daily radiant exposure (daily sums) will be presented for a period of up to 5 years, in order to indicate differences caused by location and local meteorology.
Materials and Methods
Alois W. Schmalwieser Barbara Klotz Michael Schwarzmann Dietmar J. Baumgartner Josef Schreder Günther Schauberger Mario Blumthaler
First published: 24 April 2019 https://doi.org/10.1111/php.13111
SECTIONSePDFPDFTOOLS SHARE
Abstract
The ultraviolet‐A (UVA) part of the solar spectrum at the Earth's surface is an essential environmental factor but continuous long‐time monitoring of UVA radiation is rarely done. In Austria, three existing stations of the UV monitoring network have been upgraded with UVA broadband instruments. At each station, one instrument measures global UVA irradiance and—in parallel—a second instrument measures diffuse irradiance. Recent and past measurements are available via a web page. This paper describes the used instruments, calibration and quality assurance and control procedures. Global and diffuse UVA measurements during a period of up to 5 years are presented. Data indicate clear annual courses and an increase of UVA with altitude by 8–9% per 1000 m. In the first half of the year, UVA radiation is higher than in the second half, due to less cloudiness. In Vienna (153 m asl), the mean daily global UVA radiant exposure in summer is almost as high as at Mt. Gerlitzen (1540 m asl), equalizing the altitude effect, due to less cloudiness. However, in winter, the UVA radiant exposure at Mt. Gerlitzen is double as high, as in Vienna.
Introduction
The ultraviolet‐A (UVA) range (315–400 nm) of the solar spectrum is rarely a topic of continuous monitoring, although UVA is highly important for plants, animals and humans. More common are measurements at certain wavelengths in the UVA range to characterize atmospheric conditions by spectroradiometers (e.g. 1) or narrowband filter radiometers (e.g. 2) and of course most common are measurements of the UV index (e.g. 3). A possible reason for the almost complete lack of UVA monitoring might be that the effects on livings from UVA radiation appear less dramatic than those from the ultraviolet‐B (UVB) radiation (e.g. erythema or skin cancer). However, the photobiological and ecological impact of the UVA radiation is as wide as of the UVB radiation.
The visual sense of many animal species is sensitive to UVA radiation, due to an UV sensitive photoreceptor and an UV transmissive lens. Visual perception in the UVA range is long known in invertebrates 4, 5 and fish 6, 7, was discovered in birds and reptiles in the 1980s 8, 9 and has in the meanwhile been even recognized in some mammalian species (e.g. ferret, reindeer 10). A change of UVA radiation results in a change in the color perception of these animals 11. For farm animals and animals that are kept indoors (e.g. zoo, aviary, terrarium), the availability and quality of UVA radiation are important to ensure their well‐being. However, the data available on natural levels of UVA radiation are very limited.
In respect to human and mammalian skin, UVA radiation initiates pigmentation (e.g. 12), which protects the skin from the sun to a certain extent 13, but UVA radiation also contributes effectively to skin aging and wrinkling 14, which may be cosmetically undesirable or even become pathogenic.
Already repeated low exposure to UVA radiation leads to measureable alterations 15, 16.
Inside the skin, UVA radiation affects the lipids of cells, which results in a decreased cell metabolism. Furthermore, UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which can damage DNA. Additionally, UVA radiation is the main trigger for photosensitivity reactions (e.g. phototoxicity and photoallergy 17). As UVA radiation transmits deeper into the skin (dermis) and into the eye (e.g. 18) than UVB radiation, a significantly larger amount of cells, as well as other tissues (e.g. macular degeneration 19), can be stroked by photons.
UVA radiation also penetrates more deeply into other mediums like water, plant crops or clothes. For considering UV exposure in everyday life, it has also to be taken into account that glasses (e.g. 20) of windows and windows of vehicles 21 are partially transmissive for UVA radiation. Due to this, people are exposed to UVA radiation, while shielded from UVB radiation.
The amount of UVA radiation reaching the earth's surface is magnitudes greater than that of UVB radiation (e.g. 22). Therefore, UVA radiation makes a significant contribution to photobiological effects (like nonmelanoma skin cancer, cataract 23 or immunosuppression 24), even if its effectivity is much lower than that of the UVB radiation.
An important vital effect initiated by UVA radiation is photorepair of DNA damage in plants (e.g. 25), but also in microorganisms (e.g. 26). Therefore, the ratio between the damaging UVB radiation and repairing UVA radiation becomes important. In the case of microorganism, the ratio between photoinactivation and photorepair changes throughout the year (e.g. 27), which may lead to periods which favor the spreading of microorganisms and periods which restrain the spreading. This may result in a reduction or enhancement of airborne infection diseases. There are some hints that the ratio of solar UVB and UVA radiation may be responsible for the spread of influenza A during the winter 28.
Interest in solely measuring UVA radiation was aroused, as the application of UVA radiation became common in phototherapy of certain skin diseases like psoriasis. This happens in conjunction with photosensitizing substances like psoralen. Therefore, several studies were undertaken to investigate the intensity of natural solar UVA radiation for comparison with UVA radiation from artificial sources to avoid overexposure of patients (e.g. 29). Also, in some of the internationally recognized regions for heliotherapy (e.g. psoriasis, atopic dermatitis, vitiligo) like the Dead Sea basin (e.g. 30) or Cyprus (e.g. 31), UVA radiation is a matter of interest.
Another application where UVA radiation measurements are necessary is SODIS (solar water disinfection) 32. SODIS is a low‐cost alternative, especially in southern regions, to the disinfection by mercury‐vapor‐pressure lamps which emit in the more effective UVC and UVB range. Here, irradiance measurements are used to calculate the gained fluence (e.g. 33), respectively, the duration of irradiation needed to ensure disinfection.
A variety of studies focusing on the nature of environmental solar UVA radiation and its influencing factors have been carried out in the past.
It was shown that the spatial variation of sky radiance in the UVA range (e.g. 34) can take a factor of 10. Generally, clouds and aerosols reduce UVA radiation (e.g. 35, 36). However, under broken cloud conditions, UVA radiation can be enhanced (e.g. 37), compared to clear sky. Albedo is another influencing factor (e.g. 38) that changes with time (e.g. snow cover). Global UVA radiation increases significantly with altitude (e.g. 39-42). Especially in alpine regions, there is a complex interaction between clouds, albedo and altitude (e.g. 43).
The ongoing global climate change does not affect the biosphere homogeneously. Changes occur on different spatial and temporal scales (e.g. seasonal change of cloud cover) and progress with different speeds. These also affect the amount of incoming UV radiation and its biological effectiveness (e.g. 44). Reliable long‐term monitoring is necessary in conjunction to a certain spatial resolution to make changes visible and evident.
In Austria, continuous online UV monitoring started in 1998 on behalf of the Austrian Ministry of Environment by establishing the Austrian UV index network 45. So‐called biometers have been utilized, which are broadband radiometers with erythema‐like spectral sensitivity (Model 501, Solar Light Inc., USA; 46). Locations of stations were selected by an objective method 47 in order to cover the whole country under special consideration of its geographical features, like the Alps. Today, the network consists of 13 stations and another 6 stations from neighboring countries participate in the online monitoring. These biometers mainly give information about the UVB range, due to their spectral response. So in a next step, the network was expanded by UVA broadband radiometers, which were placed aside the biometers at three stations. Today, at each of these stations, a UVA broadband radiometer measures global irradiance (sum of direct and diffuse radiation), while a second one is equipped with a shadow ring and only measures diffuse irradiance in parallel.
An important topic in monitoring is the quality of data and comparability. In this paper, we will introduce the applied methods for quality assurance and control including characteristics of instruments and calibration. Measurements and an analysis of global and diffuse UVA irradiance and daily radiant exposure (daily sums) will be presented for a period of up to 5 years, in order to indicate differences caused by location and local meteorology.
Materials and Methods
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