Radiation Amplification Factor Research Articles

Factors affecting solar ultraviolet irradiance measured since 1990 at Thessaloniki, Greece

Factors affecting the solar spectral ultraviolet (UV) irradiance at Thessaloniki, Greece were investigated using measurements with single- and double-monochromator Brewer spectroradiometer, which started operating respectively in 1989 and 1993 and continue up to the present. The two data records were quality controlled, homogenized and finally merged into one dataset, which was used in the analysis. Subsets of these data corresponding to different solar zenith angles (SZAs) and to cloud-free skies were used to quantify the long-term changes in surface UV irradiance at different wavelengths, and the importance of the factors responsible for these changes is discussed. It is shown that the calculated UV changes vary with SZA due to the different atmospheric path of the photons and the dependence of the diffuse to direct irradiance ratio on the SZA. The effect of total ozone and aerosols on UV irradiance is examined and the corresponding radiation amplification factors (RAFs) at the various wavelengths are calculated. The observed changes in UV irradiance due to ozone are smaller than those expected for the changes in total ozone, suggesting that the influence of the ozone is masked by other factors. An important finding of this study is that the improvement in air quality at Thessaloniki, during the period under examination, is the main reason for the observed increase in solar UV irradiance.

Surface solar ultraviolet irradiance and total ozone during summertime

An anticorrelation between total ozone and UV‐B radiation was observed in Athens, Greece (35.59° N, 23.44° E) for clear‐sky conditions during the summertime period 1993–2006. The UV‐B radiation (290–320 nm) was measured using a UV‐B pyranometer, and the total ozone column data were obtained using the Dobson No. 118 spectrophotometer. In addition, a parametric model has been used for the calculation of the direct and diffuse solar ultraviolet radiation reaching the Earth's surface. Finally, the total ozone observations made by the satellite‐borne instrument Scanning Imaging Absorption Spectrometer for Atmospheric Chartography were used in order to confirm the results obtained from the Dobson measurements. The main finding which stems from these data is that there is no significant seasonality in the radiation amplification factor of UV‐B, broadband UV, and the erythemally weighted UV, whereas the enhanced UV‐B generates intensive air‐pollution episodes, which subsequently attenuate the surface UV‐B irradiance. Furthermore, these findings may be used for the prediction of the propagation parameters of the microwaves, mm‐waves and optical telecommunication signals over the Athens Metropolitan Area.

Determination of radiation amplification factor of atmospheric aerosol from the surface UV irradiance measurement at Gwangju, Korea

This study investigated the impact of atmospheric aerosols on surface ultraviolet (UV) irradiance at Gwangju, Korea (35°13′N, 126°50′E). Data analyzed included surface UV irradiance measured by UV radiometers from June 1998 to April 2001 and the aerosol optical depth (AOD) in the visible range determined from a rotating shadow-band radiometer (RSR). The radiation amplification factor (RAF) of ozone for UV-B (280–315 nm) at Gwangju was 1.32–1.62. Values of the RAF of aerosols (RAFAOD) for UV-A and UV-B were 0.18–0.20 and 0.22–0.26, respectively.

New approach to radiation amplification factor

One important factor for the estimation of climate change is the Radiation Amplification Factor (RAF) defined as the percentage increase in UVbio that would result from 1% decrease in the column amount of atmospheric ozone [1,2]. RAF can generally be used only to estimate effects of small ozone changes, e.g. of a few percent, because the relationship between ozone and UVbio becomes non-linear for larger ozone changes. In other words RAF is ratio of relative changes of UVbio and the ozone column. We can say also that RAF is differential slope of UVbio to the ozone column relationship in log-log scale. It is necessary to note that the main peculiarity of this approach is its dimensionless properties. This enables us to compare values with various and different physical meanings. RAF values can give additional possibilities or information. A detailed and comparative analysis of dimensionless RAF values (from the point of denentionless nature) can give the following results. 1) A relatively strong influence and superlinear dependence is observed for: skin erythema, photocarcinogenesis, fish melanoma, generalized DNA damage, mutagenicity and fibroblast killing, cyclobutane pyrimidine dimer formation, occupational exposure limits, membrane-bound K+-stimulated ATPase inactivation, isoflavonoid formation in bean, inhibition of motility (Euglena gracilis), tropospheric photolysis O3+hn-O(D')+O2. 2) An approximately linear dependence was found for: SKH-1 corrected for human skin transformation, elastosis, damage to cornea, immune suppression, tropospheric photolysis HNO3+hn-OH+HNO2, photodegradation of nitrate ions, photodegradation of HCHO (Biscayne Bay), UVB (280–315 nm). 3) A weak dependence is for: fibroblast killing, substrate binding in Chinese hamster, DNA damage in Alfalfa, tropospheric photolysis H2O2+hn-OH+OH, HCHO+hn-H+CHO, yellowness induction in polycarbonate. 4) A very weak dependence was found for: melanoma in fish, photosynthettic electron transport, inhibition in photosynthesis (Phaoedactylum sp.), tropospheric photolysis O3+hn-O(3P)+O2, HCHO+hn-H2+CO, photoproduction of H2O2 in fresh water.

Solar UV-B Irradiance at a Tropical Indian Station,Visakhapatnam (17.70°North, 83.30°East) - a Relation with TOMS Ozone

Hourly mean values of incoming UV-B irradiance measured by UV-B Photometer at Visakhapatnam (17.70°N, 83.30°E) were analyzed and the variability of incoming UV-B irradiance with solar zenith angle and total column ozone is investigated in terms of RAF (Radiation Amplification Factor) for three wavelengths 310,290 and 280 nm. A regression model for estimating UV-B irradiance from TOMS ozone, air-mass, sun-earth distance correction and solar zenith angle was developed for this station. With the developed model long-term variation of incoming UV-B irradiance for the period 1978 - 1993 was evaluated using TOMS ozone. A study was carried out on the possible effect of UV-B irradiance on human beings (erythema) in terms of RAF and solar zenith angle which indicated higher erythemal sensitivity at lower solar zenith angles.

The total ozone and UV solar radiation over Stara Zagora, Bulgaria

The results from direct ground-based solar UV irradiance measurements and the total ozone content (TOC) over Stara Zagora (42° 25′N, 25° 37′E), Bulgaria are presented. During the period 1999–2003 the TOC data show seasonal variations, typical for the middle latitudes – maximum in the spring and minimum in the autumn. The comparison between TOC ground-based data and Global Ozone Monitoring Experiment (GOME) satellite-borne ones shows a seasonal dependence of the differences between them. A strong negative relationship between the total ozone and the 305 nm wavelength irradiance was found. The dependence between the two variables is significant ( r = −0.62 ± 0.18) at 98% confidence level. The direct sun UV doses for some specific biological effects (erythema and eyes) are obtained. The estimation of the radiation amplification factor RAF shows that the ozone reduction by 1% increases the erythemal dose by 2.3%. The eye-damaging doses are more influenced by the TOC changes and in this case RAF = −2.7%. The amount of these biological doses depended on the solar altitude over the horizon. This dependence was not so strong when the total ozone content in the atmosphere was lower.

지표 자외선 복사 변화에 미치는 오존 전량, 구름 및 적설 효과

Total solar irradiance (750), total UV irradiunce (TUV) and erythemal UV irradiance (EUV) measured at King Sejong station <TEX>$(62.22^{\circ}S,\;58.78^{\circ}W)$</TEX> in west Antarctica have been used together with total ozone, cloud amount and snow cover to examine the effects of ozone, cloud and snow surface on these surface solar inadiunce over the period of 1998-2003. The data of three solar components for each scan were grouped by cloud amount, n in oktas <TEX>$(0{\leq}n<3,\;3{\leq}n<4,\;4{\leq}n<5,\;5{\leq}n<6,\;6{\leq}n<7\;and\;7{\leq}n<8)$</TEX> and plotted against solar zenith angle (SZA) over the range of <TEX>$45^{\circ}\;to\;75^{\circ}$</TEX>. The radiation amplification factor (RAE) is used to quantify ozone effect on EUV. RAF of EUV decreases from 1.51 to 0.94 under clear skies but increases from 0.94 to 1.85 under cloudy skies as SZA increases, and decreases from 1.51 to 1.01 as cloud amount increases. The effects of cloud amount and snow surface on EUV are estimated as a function of SZA and cloud amount after normalization of the data to the reference total ozone of 300 DU. In order to analyse the transmission of solar radiation by cloud, regression analyses have been performed for the maximum values of solar irradiance on clear sky conditions <TEX>$(0{\leq}n<3)$</TEX> and the mean values on cloudy conditions, respectively. The maximum regression values for the clear sky cases were taken to represent minimum aerosol conditions fur the site and thus appropriate for use as a normalization (reference) factor for the other regressions. The overall features for the transmission of the three solar components show a relatively high values around SZAs of <TEX>$55^{\circ}\;and\;60^{\circ}$</TEX> under all sky conditions and cloud amounts <TEX>$4{\leq}n<5$</TEX> and <TEX>$5{\leq}n<6$</TEX>. The transmission is, in general, the largest in TUV and the smallest in EUV among the three components of the solar irradiance. If the ground is covered with snow on partly cloudy days <TEX>$(6{\leq}n<7)$</TEX>, EUV increases by 20 to 26% compared to snow-free surface around SZA <TEX>$60^{\circ}-65^{\circ}$</TEX>, due to multiple reflections and scattering between the surface and the clouds. The relative difference between snow surface and snow-free surface slowly increases from 9% to 20% as total ozone increases from 100 DU to 400 DU under partly cloud conditions <TEX>$(3{\leq}n<6)$</TEX> at SZA <TEX>$60^{\circ}$</TEX>. The snow effects on TUV and TSO are relatively high with 32% and 34%, respectively, under clear sky conditions, while the effects changes to 36% and 20% for TUV and TSO, respectively, as cloud amount increases.

Modeling the effect of ozone loss on photobleaching of chromophoric dissolved organic matter in the St. Lawrence estuary

Temporal trends in total ozone for the St. Lawrence estuary were estimated from ground‐based measurements at the NOAA/CMDL station in Caribou, Maine. Linear regression analysis showed that from 1979 to 1999 total ozone has decreased by about 3.3% per decade on an annual basis and ≤6.2% per decade on a monthly basis relative to unperturbed (pre‐CFC) levels. The influence of increased ultraviolet‐B (280–320 nm) radiation associated with ozone depletion on water column photochemical processes was evaluated by modeling the photobleaching of chromophoric dissolved organic material (CDOM). Linear regression analysis showed small (&lt;0.5% per decade), but statistically significant upward trends in maximum noontime photobleaching rates. Most notably, positive trends in relative rates for May, June, and July, when maximum absolute rates are expected, were predicted. A global model based on TOMS ozone data revealed increases in photobleaching of ≤3% per decade at high latitudes in the Southern Hemisphere. Radiation amplification factors for increases in photochemically weighted UV (280–400 nm) in response to ozone depletion were estimated at 0.1 and 0.08 for photobleaching of CDOM absorbance at 300 and 350 nm, respectively. Application of the laboratory‐based model to conditions that more closely resembled those in situ were variable with both overestimation and underestimation of measured rates. The differences between modeled rates and observed rates under quasi‐natural conditions were as large or larger than the predicted increases due to ozone depletion. These comparisons suggest that biological activity and mixing play an important, but as yet ill‐defined, role in modifying photochemical processes.

Sensitivity of biologically active UV radiation to stratospheric ozone changes: effects of action spectrum shape and wavelength ranges.

Biological action spectra are commonly used to assess health and ecosystem responses to increases in spectral ultraviolet (UV) irradiances resulting from stratospheric ozone (O3) reductions. For each action spectrum, a normalized sensitivity coefficient (the radiation amplification factor [RAF]) can be calculated as the relative increase in biologically active UV irradiance for a given relative decrease in the atmospheric O3 column amount. We use a detailed radiative transfer model to calculate the dependence of RAF on the O3 column amount and the solar zenith angle (and, therefore, implicitly on latitude and season) for several commonly used action spectra. A simple analytical model is used to interpret the results in terms of the semilogarithmic slope of the action spectra in the UV-B and UV-A wavelength ranges. We also show that RAF may be overestimated substantially if the UV-A portion of an action spectrum is significant but is neglected. This is illustrated using several idealized action spectra as well as published action spectra for plant responses to UV irradiation. Generally, if the portion of an action spectrum measured longward of approximately 300 nm spans less than about two orders in magnitude in its sensitivity, significant errors in the estimated RAF may ensue, and the use of this action spectrum in O3-related studies can be compromised.

A biological spectral weighting function for ozone depletion research with higher plants

Biological spectral weighting functions (BSWF) play a key role in assessing implications of stratospheric ozone reduction. They are used to calculate the increase in biologically effective solar UV radiation due to ozone reduction (radiation amplification factor, RAF), assess current latitudinal gradients of solar UV radiation, and compare solar UV radiation with that from lamps and filters used in experiments. As a basis for a BSWF, we developed an action spectrum for growth responses of light‐grown oat (Avena sativa L. cv. Otana) seedlings exposed to narrowband UV radiation from a large double water‐prism monochromator. Five UV wavelength peaks were used (275, 297, 302, 313 and 366 nm) in the absence of any visible radiation. Growth responses were measured from 1 to 10 days after the treatments. At all these wavelengths, the UV radiation inhibited height growth, including the height at which the first leaf separated from the stem. Radiation at all wavelengths used, except the one UV‐A wavelength, promoted the length of the second leaf. The resulting action spectrum closely resembles the commonly used generalized plant response function except that it indicates continued sensitivity into the UV‐A region. When used as a BSWF for the ozone depletion problem, this new function for plant growth would suggest substantially less impact of ozone depletion because it results in only a modest increment of biologically effective UV for a given level of ozone depletion (a lower RAF). Yet this new BSWF also suggests that experimental treatments based on previous BSWF with less emphasis on the UV‐A may have resulted in simulations of less pronounced ozone depletion than intended. The validity of this new BSWF with UV‐A sensitivity, designated the UV plant growth weighting function, was verified in field experiments as described in the companion paper.

Field testing of UV biological spectral weighting functions for higher plants

In biological research on the ozone depletion issue, action spectra are typically used as biological spectral weighting functions (BSWF). There has been little testing, however, of the appropriateness of different functions under realistic field conditions. Here we quantitatively evaluate a new BSWF for plant growth response to UV radiation, and other action spectra potentially usable as BSWF, in two seasons of field experiments. We utilized supplemental UV‐B radiation with various combinations of filtered solar UV‐A radiation. Our new BSWF, which we call the UV plant growth weighting function, indicates responses in the UV‐A waveband. In field tests it proved to be the most appropriate weighting function for the responses we measured in oat (Avena sativa L. cv. Otana) over the two field seasons in these studies. A 10‐day field experiment with canola, Brassica rapa L. cv. Goldrush, also suggested substantial effects of both UV‐B and UV‐A radiation on growth. If this new UV plant growth BSWF proves to be appropriate for many plant species, it represents a lower radiation amplification factor (RAF) than several previously used weighting functions for plants. This means less change in biologically effective UV for each increment of ozone column change. However, the lower RAF also means that experiments utilizing supplemental UV treatments have supplied milder doses of additional UV than intended, since they were based on BSWF that overemphasized UV‐B and ignored the UV‐A region. While we await continued field testing of BSWF on diverse taxa, we recommend: (1) reporting weighted irradiance with our new BSWF, and other appropriate functions; (2) continued reporting of the generalized plant weighted UV for continuity and comparative purposes, since it has been so widely used.

Effects of desert dust and ozone on the ultraviolet irradiance at the Mediterranean island of Lampedusa during PAUR II

Observations of the ultraviolet spectral irradiance, tropospheric aerosols, and ozone were carried out at Lampedusa (35.5°N, 12.6°E), during May and June 1999, in conjunction with the Photochemical Activity and Ultraviolet Radiation modulating factors II experiment. Lampedusa is a small Italian island in the Mediterranean, about 100 km off the west coast of Tunisia, North Africa. During the campaign, aerosol transport from Sahara, mainly controlled by the development of high‐pressure systems over North Africa, strongly affected the troposphere at Lampedusa. Aerosol optical depths at 415 nm ranged between 0.14 and 0.91. Dust aerosols with an optical depth of 0.5 at 415 nm produced a reduction of the measured irradiance at 350 nm by about 20%, at a solar zenith angle of 30°, and by about 25% at 60°. The occurrence of large aerosol optical depths was associated with low total ozone values, mainly due to the influence of surface pressure on the stratospheric vertical structure and transport. Thus the aerosol attenuation of the UV irradiance was large when low absorption by ozone occurred, and a large ozone absorption occurred when aerosol attenuation was small. Mostly because of their large variability, aerosols produce larger attenuation effects than ozone on the UV irradiance for wavelengths longer than 315 nm. By neglecting the influence of aerosols on the radiation amplification factors, calculation of the dependence of the UV irradiance on ozone can be significantly underestimated. For the erythemally weighted irradiance a value for the radiation amplification factor between −0.1 and 0.7, depending on the solar zenith angle, has been derived. A simple model to take into account the aerosol effect in the determination of the radiation amplification factor has been developed. By applying this model an erythemal radiation amplification factor between 0.8 and 1.25 is obtained. It is estimated that an aerosol layer of optical depth 0.5 at 415 nm produces a reduction of the erythemal irradiance as large as 25 and 27% at solar zenith angles of 30° and 60°, respectively. When conditions similar to those of Lampedusa occur, i.e., when large aerosol loads may be present, and for certain meteorological conditions, the effects of the aerosol on the surface ultraviolet irradiance cannot be neglected.

The role of UV-B radiation in aquatic and terrestrial ecosystems—an experimental and functional analysis of the evolution of UV-absorbing compounds

The role of UV-B radiation in aquatic and terrestrial ecosystems—an experimental and functional analysis of the evolution of UV-absorbing compounds

Analysis of UV‐B irradiances measured simultaneously at two stations in the Czech Republic

The 10 min sums of erythemal UV‐B irradiances measured during approximately 10 months at two locations with different altitudes were analyzed. The magnitude of the altitude effect averaged over the whole period varies between 4 and 8%/1000 m. The value of radiation amplification factor (RAF) derived from the relationship between UV‐B irradiance and total ozone is about 1.1. The value of RAF is slightly higher if derived from the relationship between the ratio of UV‐B to global solar irradiance and total ozone. A statistical model relating clear‐sky UV‐B irradiance with solar zenith angle, total ozone, and Julian day was developed. Unfortunately, knowledge of the daily average total column ozone does not adequately improve the forecast of UV‐B irradiance.

Depth-dependent photoacclimatization to solar ultraviolet radiation in the Caribbean coral Montastraea faveolata

The importance of solar ultraviolet radiation (UVR, 290 to 400 nm), and UVB (290 to 320 nm) in particular, as an environmental factor affecting the biology and ecology of coral reefs has taken on renewed interest since the demonstration of global stratospheric ozone loss through human activities. The hermatypic coral Montastraea faveolata occurs over a wide bathymetric range in the Florida Keys reef tract. The bathymetric range of M. faveolata and its role in reef community structure make it an important species for which to assess the effects of present day UVR irradiances. Both UVR irradiances and UVR-absorbing mycosporine-like amino acids (MAAs) decreased significantly with increasing depth in M. faveolata. UVB irradiances were measured to a depth of 30 m during this study and maximum rates of productivity in M. faveolata were significantly affected by the presence of UVR. Action spectra (= biological weighting function) for the photoinhibition of photosynthesis by UVR were measured for samples of M. faveolata at 3, 10, 18, 23, and 30 m. Using these action spectra, radiation amplification factors (RAFs) were calculated for corals at the same depths. RAFs for M. faveolata suggest that corals at depths greater than 3 m will be more sensitive to increases in UVB irradiance, such as might be caused by ozone depletion, than their shallow-water counterparts. Despite this increase in sensitivity to UVB, calculations incorporating continued ozone depletion suggest that at the present rate of stratospheric ozone depletion corals deeper than 5 m in the Florida Keys will be affected very little, if at all, by increases in UVR. These results, however, do not incorporate the interacting and synergistic effects of UVR with other physical parameters (e.g. temperature) that will be essential to understanding and predicting the fate of coral reefs under conditions of global change.

Time Modeling of Daily UVB Values in Madrid, Spain

Abstract This paper presents the daily solar ultraviolet-B (UVB) values measured in Madrid, Spain, during the period 1994–97 with a Brewer MKIV spectrophotometer. The range of the measured values was 0.042–6.41 kJ m−2. A description of the values is shown. Periodicities of 7 and 3 days, associated with synoptic patterns, are significant. Ozone (with 5- and 3-day periodicities) and cloudiness also are studied for the same period; their association with UVB is investigated. The radiative amplification factor value between UVB and ozone is 0.62. The correlation coefficient between UVB and a cloudiness index [equal to one minus the (number of sun hours divided by the number of theoretical sun hours)] is −0.57. A time series model describing the UVB series is shown. It is useful in estimating the UVB values, even on days when radiation values are not available. It provides accurate performance, can be used any day of the year, and has no main restrictions for its application. Thus, this kind of model can be a ...

Impact of total ozone variability on surface solar ultraviolet radiation change. implication for ocular damage

We have used the daily observations made by Total Ozone Mapping Spectrometer (TOMS) on Nimbus 7, over St. Petersburg (60°N, 30°E), Russia, in order to investigate the increase in the daily broad‐band solar ultraviolet radiation (SUVR) reaching the ground for the time period 1979–1992. This investigation has been performed by examining the seasonal variation of the radiation amplification factor. This examination provides a better understanding for the impacts of the enhanced SUVR on the human eyes in the view of recently obtained experimental results.

New observations of ultraviolet radiation and column ozone from Socorro, New Mexico

Measurements of surface ultraviolet irradiances are presented for the period of June 1997 to December 1998 from Socorro, NM (34°N, 107°W). The observations are used with results of radiative transfer calculations to retrieve total column ozone. Mean differences between Socorro daily ozone measurements and Earth Probe TOMS satellite data are −1.8 DU and 0.6 DU for 1997 and 1998, respectively. Unusually low ozone was observed in late November and December of 1998, with levels near or below the lowest ozone in the 17‐year Nimbus‐7 and Earth Probe TOMS record for this location. The clear‐sky correlation between the UV Index at 60° solar zenith angle and total ozone is well described by a power law, with an exponent (Radiation Amplification Factor) of 0.97±0.16. One exception occurred during a 10‐day period in December 1997 and January 1998 in the aftermath of a heavy snow storm, when the UV Index exhibited clear‐sky enhancements of up to 30%. Increases in downwelling ultraviolet radiation were related to a higher effective surface albedo with maximum estimated values between 0.7 to 0.9.

Investigating biological response in the UVB as a function of ozone variation using perturbation theory

In order to determine a biological response to ultraviolet radiation, calculations of biologically weighted dose rates are required, which in turn involve the integral over wavelength of an action spectrum multiplied by appropriate surface flux data. To determine a biologically weighted dose rate accurately, a reasonable wavelength resolution is required, involving a full radiative transfer solution to be performed for each wavelength in order to obtain the surface flux information. If biologically weighted dose rates are needed as a function of ozone variation, then the number of radiative transfer solutions quickly makes a large number of ozone variations cumbersome. This paper shows that the perturbation theory developed for atmospheric radiative transfer by Box and co-workers can predict surface fluxes and hence biologically weighted dose rates for a large range of ozone variations very efficiently. The method is then extended to calculate radiation amplification factors. Results for biologically weighted dose rates are presented for a large range of solar zenith angles and ozone loadings using perturbation theory and a full radiative transfer code and show that the perturbation predictions never deviate very far from the radiative transfer solutions.

UV measurements at Mauna Loa: July 1995 to July 1996

A UV spectroradiometer was installed at Mauna Loa Observatory (MLO), Hawaii, in July 1995. This instrument, based on a commercially available double monochromator, uses a diffuser mounted as a horizontal receptor inside a quartz dome and views the whole sky. The instrument scans over the 290–450 nm spectral range with a band pass of about 1 nm for each 5° of solar zenith angle (SZA). The UV irradiances measured at MLO are much more intense than at low‐altitude midlatitude locations. For observations at SZA 45° the erythemally weighted UV irradiances can exceed 21 μW cm−2, which is approximately 15–20% greater than that seen at Lauder, New Zealand, for similar ozone amounts. The difference is primarily due to the higher altitude at MLO (3.4 km). For overhead Sun conditions at MLO the largest value of erythemal UV was 51.3±3.1 μW cm−2, which to our knowledge is the highest recorded any‐where at the Earth's surface. UV irradiance is strongly correlated (inversely) with Dobson spectrophotometer total ozone measurements at MLO, with higher correlations at shorter wavelengths. The radiative amplification factor (RAF) for erythema at MLO is about 1.33±0.2 at SZA 45°.