Factors affecting solar ultraviolet irradiance measured since 1990 at Thessaloniki, Greece
ABSTRACT 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.
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ABSTRACT: The Montreal Protocol is working, but it will take several decades for ozone to return to 1980 levels. The atmospheric concentrations of ozone depleting substances are decreasing, and ozone column amounts are no longer decreasing. Mid-latitude ozone is expected to return to 1980 levels before mid-century, slightly earlier than predicted previously. However, the recovery rate will be slower at high latitudes. Springtime ozone depletion is expected to continue to occur at polar latitudes, especially in Antarctica, in the next few decades. Because of the success of the Protocol, increases in UV-B radiation have been small outside regions affected by the Antarctic ozone hole, and have been difficult to detect. There is a large variability in UV-B radiation due to factors other than ozone, such as clouds and aerosols. There are few long-term measurements available to confirm the increases that would have occurred as a result of ozone depletion. At mid-latitudes UV-B irradiances are currently only slightly greater than in 1980 (increases less than ~5%), but increases have been substantial at high and polar latitudes where ozone depletion has been larger. Without the Montreal Protocol, peak values of sunburning UV radiation could have been tripled by 2065 at mid-northern latitudes. This would have had serious consequences for the environment and for human health. There are strong interactions between ozone depletion and changes in climate induced by increasing greenhouse gases (GHGs). Ozone depletion affects climate, and climate change affects ozone. The successful implementation of the Montreal Protocol has had a marked effect on climate change. The calculated reduction in radiative forcing due to the phase-out of chlorofluorocarbons (CFCs) far exceeds that from the measures taken under the Kyoto protocol for the reduction of GHGs. Thus the phase-out of CFCs is currently tending to counteract the increases in surface temperature due to increased GHGs. The amount of stratospheric ozone can also be affected by the increases in the concentration of GHGs, which lead to decreased temperatures in the stratosphere and accelerated circulation patterns. These changes tend to decrease total ozone in the tropics and increase total ozone at mid and high latitudes. Changes in circulation induced by changes in ozone can also affect patterns of surface wind and rainfall. The projected changes in ozone and clouds may lead to large decreases in UV at high latitudes, where UV is already low; and to small increases at low latitudes, where it is already high. This could have important implications for health and ecosystems. Compared to 1980, UV-B irradiance towards the end of the 21st century is projected to be lower at mid to high latitudes by between 5 and 20% respectively, and higher by 2-3% in the low latitudes. However, these projections must be treated with caution because they also depend strongly on changes in cloud cover, air pollutants, and aerosols, all of which are influenced by climate change, and their future is uncertain. Strong interactions between ozone depletion and climate change and uncertainties in the measurements and models limit our confidence in predicting the future UV radiation. It is therefore important to improve our understanding of the processes involved, and to continue monitoring ozone and surface UV spectral irradiances both from the surface and from satellites so we can respond to unexpected changes in the future.Photochemical and Photobiological Sciences 02/2011; 10(2):182-98. · 2.92 Impact Factor
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ABSTRACT: The surface ozone photolysis rate (J(O 1 D)) was computed on a daily basis and on a 50 km x 50 km resolution for the 11-year period 2000-2010 at Finokalia meteorological station in Crete, Greece. A radiative transfer model was used, with climatological data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra satellite. The area is representative of the Eastern Mediterranean, a region with high variability in aerosol loads and total column ozone. Instantaneous values of J(O 1 D) computed from the model were validated against corresponding station measurements available during the 5-year period 2002-2006. Monthly mean values of J(O 1 D) during the 11-year period examined, reveal a statistically significant decreasing trend, based on Terra MODIS data, which shows an overall 13% decrease. The aerosol effect on J(O 1 D) varies on a daily basis, depending on the aerosol load, and can exceed -10% during dust events, with a median value of -2.3% over the whole period examined. On a seasonal basis, the aerosol effect on J(O 1 D) follows the seasonal pattern of the aerosol load, with higher values in spring and autumn, due to the increased Saharan dust episodes during these seasons. Linear regression analysis on monthly mean values of total column ozone revealed a statistically significant increasing trend in both Finokalia and Thessaloniki stations. Total column ozone MODIS data were validated against spectroradiometric (columnar) measurements at Thessaloniki station. Sensitivity analysis on the effect of total column ozone on J(O 1 D) showed that a 10% variation in total ozone causes a corresponding 15-17% change in J(O 1 D). These results suggest that the decreasing trend in J(O 1 D) found in the case of Terra MODIS should be attributed mainly to the corresponding increasing trend in total column ozone.Atmospheric Environment 04/2013; · 3.11 Impact Factor
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ABSTRACT: The prediction of the biological effects of solar radiation on human health, in particular involving terrestrial level of solar ultraviolet (UV) radiation, requires the development of an adequate methodological strategy for remote sensing. To date, it is well understood that, in appropriate doses, UV radiation is beneficial for people, specifically due to the production of vitamin D3 in the skin from its precursor 7-dehydrocholesterol. But as far as excessive UV exposure causes acute and chronic health effects, in most cases biological activity of solar UV radiation is calculated by weighting solar UV spectra with International Commission on Illumination (CIE) erythemal action spectrum. Yet the beneficial vitamin D synthetic capacity of sunlight cannot be correctly estimated in this way because of the significant difference between the erythemic and vitamin D synthesis action spectra. With due regard to the essential role of vitamin D3 for human health, in this article we examine the possibility of simplified estimation in situ of provitamin D3 photoconversion into previtamin D3 from the UV absorption spectra of an in vitro model of vitamin D synthesis upon exposure to sunlight. A large-scale linear correlation (R = 0.99) was found on a clear summer day between the concentration of accumulated previtamin D3 and maximum absorbance decline in the initial provitamin D3 absorption spectrum. However, long-term observations showed a poorer (R = 0.77) correlation, and a source of ambiguity of such indirect estimation of previtamin D3 concentration is discussed in detail. In addition, we propose a reliable algorithm for the direct calculation of previtamin D3 accumulation using solar UV spectra as input data to the reaction model of previtamin D photosynthesis and demonstrate the critical dependence of previtamin D3 accumulation on stratospheric ozone, season, latitude and cloudiness. The comparison of experimental and simulation data conforms to recent findings on Europe's darker atmosphere in the UV-B and implicates the practical certainty of the presented algorithm for the calculation of the vitamin D synthetic capacity from the remotely sensed solar spectra.International Journal of Remote Sensing - INT J REMOTE SENS. 01/2011;