Spectral measurements of direct solar ultraviolet irradiance are very important for many applicat... more Spectral measurements of direct solar ultraviolet irradiance are very important for many applications in the field of atmospheric sciences. Despite its usefulness, few UV monitoring sites include such measurements in their regular observational programs. Standardization of measurement methodologies and calibration techniques is required in order to reach the quality standard of global irradiance measurements. This study presents preliminary results from an intercomparison campaign of seven UV spectroradiometers of different types that ...
ABSTRACT The risk assessment of detrimental effects of solar UV radiation requires a detailed kno... more ABSTRACT The risk assessment of detrimental effects of solar UV radiation requires a detailed knowledge of the intensity and the spectral composition of global radiation reaching the Earth's surface. Both quantities exhibit large variations in time and location. Some of the variations are very regular because they are directly related to the Earth's position on her orbit around the sun, to the angle the Earth's axis makes with the orbital plane and of course, to the daily rotation around the axis. After entering the atmosphere radiation is modified by various absorption and scattering processes. The changes in atmospheric constituents which are involved in these processes also contribute to the variability of global radiation. The stratospheric ozone layer is surely the most important absorber for shortwave UV radiation. Therefore, its changes—mainly due to human activities—have a direct impact on the amount of UV radiation responsible for sunburn or even skin cancer. In the lower atmosphere, clouds are the main factor which modulate global radiation. The temporal and spatial changes in atmospheric parameters are much less predictable than astronomical and geometrical ones. Local parameters like altitude or surface albedo further modify the ambient UV climate. Our knowledge of the long-term and the short-term dynamics of UV radiation has tremendously increased by recent progress made both in the precision of UV measurements and the mathematical modeling of radiation transport through the atmosphere. This chapter reviews various physical aspects of solar radiation reaching the Earth's surface.
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...
Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies... more Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies. The relative efficiency of this detector does not exactly match the action spectrum as proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and to which the UV dose and exposure limits refer. Therefore, the calibration of the dosemeter depends on the spetrum. In the present paper the variation of the calibration factor for terrestrial solar UV spectra is analysed on the basis of a two year observation period at a site near Munich. Germany. A detailed error estimation is included. It is shown that the variation of the calibration factor within this class of spectra is the main contribution to the total uncertainty of the dose determination, which can be up to 40%. The shape of the spectrum of terrestrial solar UV radiation is mainly determined by the total ozone column and the solar elevation angle. It is shown how the calibration depends on these two parameters and how this additional information can help to reduce the measurement error to a residual uncertainty of 17%. Exposure studies of terrestrial solar UV radiation using polysulphone film as a dosemeter would gain in accuracy if total ozone column values at the study's site could be measured or taken from satellite or weather service data. The interpretation of the magnitude of the dose uncertainty depends on the further use of these data.
ABSTRACT Ecological plant experiments using artificial light sources require careful shaping of t... more ABSTRACT Ecological plant experiments using artificial light sources require careful shaping of the spectral irradiance. This includes the steep UV-absorption characteristics resulting from the filtering of solar radiation by atmosphefic ozone. Borosilicate and soda-lime glass filters screen radiation very similarly to ozone. They have a high mechanical stability and are available in large filter sheets and are, therefore, suited for the simulation of future scenarios of enhanced solar UV-B radiation in large scale vegetation stress experiments. Although such filters meet many requirements of light engineering, there are limitations due to the slope of the UV-edge and due to solarisation effects. Thus, the interpretation of the artifical radiation spectra and their comparison to UV scenarios of decreasing stratospheric ozone need careful discussion. Different methods to classify spectra of artificial UV-radiation are presented, and a new classification by a cut-off wavelength of the UV-edge and its slope is introduced.
ABSTRACT Routinely monitored radiation parameters, including those at UV wavelengths, most common... more ABSTRACT Routinely monitored radiation parameters, including those at UV wavelengths, most commonly refer to irradiance, that is the radiation incident on a flat horizontal plate. However, in the study of atmospheric chemistry, where UV radiation is a prime photochemical driver, the target molecules are approximately spherical and the actinic flux (radiation on the surface of a sphere) is a better measure of the effective radiation. Unfortunately actinic flux measurements (also known as scalar irradiance) are uncommon research measurements. The ability to convert irradiance data to actinic flux data within a reasonable degree of uncertainty would provide an actinic flux database mapped from existing irradiance databases, thus vastly increasing knowledge of actinic flux variability and climatology. Synchronised spectral UV irradiance and actinic flux measurements have been made during the ADMIRA project, and used to develop an empirical method for converting irradiance to actinic flux. With some prior knowledge of the sky conditions during the irradiance measurements the actinic flux can be estimated to within a few percent. If no knowledge of the sky conditions is available then the empirical method still returns actinic fluxes within 10% of those measured at the site for which the conversion was developed.
The results of what is to our knowledge the first intercomparison of seven independent spectrorad... more The results of what is to our knowledge the first intercomparison of seven independent spectroradiometers measuring solar UV irradiances are presented. The intercomparison was carried out in the GSF-Forschungszentrum für Umwelt und Gesundheit, Neuherberg (near Munich, Germany), on 13 July 1990. The spectroradiometric measurements were supplemented by other meteorological, optical, and chemical measurements at the same time. As this day was cloudless, the data can be compared with the measurements taken by Bener in Switzerland in the 1960's and with the results of radiative transfer models. The measured irradiances at noon differed by factors of up to 100. These large differences demonstrate the great difficulties with this type of measurement. Some instrument systems, however, ranged within tolerances of ±10%, thus allowing us to make recommendations for the spectroradiometry of solar UV irradiances.
Volatile organic compounds (VOCs) include saturated, unsaturated, and other substituted hydrocarb... more Volatile organic compounds (VOCs) include saturated, unsaturated, and other substituted hydrocarbons. VOCs play an important role in the chemistry of the atmosphere by influencing ozone and hydroxyl radical (OH) concentrations and the conversion rates of nitrogen oxides (NO x ). Elevated levels of VOCs and NO x have led to an approximate doubling of ozone in the lower troposphere over
Spectral measurements of direct solar ultraviolet irradiance are very important for many applicat... more Spectral measurements of direct solar ultraviolet irradiance are very important for many applications in the field of atmospheric sciences. Despite its usefulness, few UV monitoring sites include such measurements in their regular observational programs. Standardization of measurement methodologies and calibration techniques is required in order to reach the quality standard of global irradiance measurements. This study presents preliminary results from an intercomparison campaign of seven UV spectroradiometers of different types that ...
ABSTRACT The risk assessment of detrimental effects of solar UV radiation requires a detailed kno... more ABSTRACT The risk assessment of detrimental effects of solar UV radiation requires a detailed knowledge of the intensity and the spectral composition of global radiation reaching the Earth's surface. Both quantities exhibit large variations in time and location. Some of the variations are very regular because they are directly related to the Earth's position on her orbit around the sun, to the angle the Earth's axis makes with the orbital plane and of course, to the daily rotation around the axis. After entering the atmosphere radiation is modified by various absorption and scattering processes. The changes in atmospheric constituents which are involved in these processes also contribute to the variability of global radiation. The stratospheric ozone layer is surely the most important absorber for shortwave UV radiation. Therefore, its changes—mainly due to human activities—have a direct impact on the amount of UV radiation responsible for sunburn or even skin cancer. In the lower atmosphere, clouds are the main factor which modulate global radiation. The temporal and spatial changes in atmospheric parameters are much less predictable than astronomical and geometrical ones. Local parameters like altitude or surface albedo further modify the ambient UV climate. Our knowledge of the long-term and the short-term dynamics of UV radiation has tremendously increased by recent progress made both in the precision of UV measurements and the mathematical modeling of radiation transport through the atmosphere. This chapter reviews various physical aspects of solar radiation reaching the Earth's surface.
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...
Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies... more Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies. The relative efficiency of this detector does not exactly match the action spectrum as proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and to which the UV dose and exposure limits refer. Therefore, the calibration of the dosemeter depends on the spetrum. In the present paper the variation of the calibration factor for terrestrial solar UV spectra is analysed on the basis of a two year observation period at a site near Munich. Germany. A detailed error estimation is included. It is shown that the variation of the calibration factor within this class of spectra is the main contribution to the total uncertainty of the dose determination, which can be up to 40%. The shape of the spectrum of terrestrial solar UV radiation is mainly determined by the total ozone column and the solar elevation angle. It is shown how the calibration depends on these two parameters and how this additional information can help to reduce the measurement error to a residual uncertainty of 17%. Exposure studies of terrestrial solar UV radiation using polysulphone film as a dosemeter would gain in accuracy if total ozone column values at the study's site could be measured or taken from satellite or weather service data. The interpretation of the magnitude of the dose uncertainty depends on the further use of these data.
ABSTRACT Ecological plant experiments using artificial light sources require careful shaping of t... more ABSTRACT Ecological plant experiments using artificial light sources require careful shaping of the spectral irradiance. This includes the steep UV-absorption characteristics resulting from the filtering of solar radiation by atmosphefic ozone. Borosilicate and soda-lime glass filters screen radiation very similarly to ozone. They have a high mechanical stability and are available in large filter sheets and are, therefore, suited for the simulation of future scenarios of enhanced solar UV-B radiation in large scale vegetation stress experiments. Although such filters meet many requirements of light engineering, there are limitations due to the slope of the UV-edge and due to solarisation effects. Thus, the interpretation of the artifical radiation spectra and their comparison to UV scenarios of decreasing stratospheric ozone need careful discussion. Different methods to classify spectra of artificial UV-radiation are presented, and a new classification by a cut-off wavelength of the UV-edge and its slope is introduced.
ABSTRACT Routinely monitored radiation parameters, including those at UV wavelengths, most common... more ABSTRACT Routinely monitored radiation parameters, including those at UV wavelengths, most commonly refer to irradiance, that is the radiation incident on a flat horizontal plate. However, in the study of atmospheric chemistry, where UV radiation is a prime photochemical driver, the target molecules are approximately spherical and the actinic flux (radiation on the surface of a sphere) is a better measure of the effective radiation. Unfortunately actinic flux measurements (also known as scalar irradiance) are uncommon research measurements. The ability to convert irradiance data to actinic flux data within a reasonable degree of uncertainty would provide an actinic flux database mapped from existing irradiance databases, thus vastly increasing knowledge of actinic flux variability and climatology. Synchronised spectral UV irradiance and actinic flux measurements have been made during the ADMIRA project, and used to develop an empirical method for converting irradiance to actinic flux. With some prior knowledge of the sky conditions during the irradiance measurements the actinic flux can be estimated to within a few percent. If no knowledge of the sky conditions is available then the empirical method still returns actinic fluxes within 10% of those measured at the site for which the conversion was developed.
The results of what is to our knowledge the first intercomparison of seven independent spectrorad... more The results of what is to our knowledge the first intercomparison of seven independent spectroradiometers measuring solar UV irradiances are presented. The intercomparison was carried out in the GSF-Forschungszentrum für Umwelt und Gesundheit, Neuherberg (near Munich, Germany), on 13 July 1990. The spectroradiometric measurements were supplemented by other meteorological, optical, and chemical measurements at the same time. As this day was cloudless, the data can be compared with the measurements taken by Bener in Switzerland in the 1960's and with the results of radiative transfer models. The measured irradiances at noon differed by factors of up to 100. These large differences demonstrate the great difficulties with this type of measurement. Some instrument systems, however, ranged within tolerances of ±10%, thus allowing us to make recommendations for the spectroradiometry of solar UV irradiances.
Volatile organic compounds (VOCs) include saturated, unsaturated, and other substituted hydrocarb... more Volatile organic compounds (VOCs) include saturated, unsaturated, and other substituted hydrocarbons. VOCs play an important role in the chemistry of the atmosphere by influencing ozone and hydroxyl radical (OH) concentrations and the conversion rates of nitrogen oxides (NO x ). Elevated levels of VOCs and NO x have led to an approximate doubling of ozone in the lower troposphere over
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