OZONE DEPLETION AND INCREASE IN ANNUAL CARCINOGENIC ULTRAVIOLET DOSE

An increase in skin cancer incidence due to an increase of solar ultraviolet (UV) radiation is one of the best quantitated effects of stratospheric ozone depletion. Until now, estimates of effective UV dosages could not be based on spectral data on carcinogenicity. Instead the spectral dependence of sunburn or mutations was used. These data contained little information on longwave ultraviolet radiation (UVA: 315-380 nm). Recently, in hairless mice, experimental data have become available on the carcinogenic effectiveness of the ultraviolet, including UVA. From these new data we can estimate the effect of ozone depletion on the ambient annual carcinogenic UV dose. We find that a 1% decrease in ozone yields a 1.56% increase in annual carcinogenic UV; this value is not strongly dependent on geographical latitude. From this result, combined with the dose-response relationship for UV carcinogenesis, we conclude that for a 1% decrease in total column atmospheric ozone an increase of 2.7% in non-melanoma skin cancer is to be expected.     

SOLAR ULTRAVIOLET RADIATION AT THE EARTH'S SURFACE

The biologically effective ultraviolet irradiance at the earth's surface varies with the elevation of the sun, the atmospheric ozone amount, and with the abundance of scatterers and absorbers of natural and anthropogenic origin. Taken alone, the reported decrease in column ozone over the Northern Hemisphere between 1969 and 1986 implies an increase in erythemal irradiance at the ground of four percent or less during summer. However, an increase in tropospheric absorption, arising from polluting gases or particulates over localized areas, could more than offset the predicted enhancement in radiation. Any such extra absorption is likely to be highly regional in nature and does not imply that a decrease in erythemal radiation has occurred on a global basis. The Antarctic 'ozone hole' represents a special case in which a portion of the earth has experienced ultraviolet radiation levels during spring that are far in excess of those which prevailed prior to the present decade.     

POSSIBLE LONG-TERM CHANGES IN BIOLOGICALLY ACTIVE ULTRAVIOLET RADIATION REACHING THE GROUND

Abstract— Three scenarios for long-term changes in atmospheric ozone over the time period 1960 to 2030 lead to different projections for the ultraviolet radiation flux at the earth's surface. Biologically effective fluxes for damage to DNA and generalized damage to plants vary by a factor of 10 or more with latitude and season irrespective of possible changes in ozone. The natural latitudinal gradient in radiation corresponds to spatial changes in biologically effective fluxes which are large compared to temporal changes expected from trends in ozone over the time period analyzed. In an extreme scenario of ozone change, based on an assumed increase in chlorofluorocarbon release rates of 3% per year after 1980, the annually integrated effective flux for damage to DNA increases by 13.5% at latitude 40°N between 1960 and 2030. With chlorofluorocarbon release rates held fixed at their 1980 values, the corresponding radiation increase is only 2.3%. In a scenario where atmospheric chlorine remains fixed at its 1960 value, trends in atmospheric methane and nitrous oxide imply a decrease in biologically effective flux at 40°N of 5.3% between 1960 and 2030.     

Photoreactivation in Paramecium tetraurelia under conditions of various degrees of ozone layer depletion

Photoreactivation (PR) is an efficient survival mechanism that helps protect cells against the harmful effects of solar-ultraviolet (UV) radiation. The PR mechanism involves photolyase, just one enzyme, and can repair DNA damage, such as cyclobutane-pyrimidine dimers (CPD) induced by near-UV/blue light, a component of sunlight. Although the balance of near-UV/blue light and far-UV light reaching the Earth's surface could be altered by the atmospheric ozone layer's depletion, experiments simulating this environmental change and its possible effects on life have not yet been performed. To quantify the strength of UVB in sunlight reaching the Earth's surface, we measured the number of CPD generated in plasmid DNA after UVB irradiation or exposure to sunlight. To simulate the increase of solar-UV radiation resulting from the ozone layer depletion, Paramecium tetraurelia was exposed to UVB and/or sunlight in clear summer weather. PR recovery after exposure to sunlight was complete at a low dose rate of 0.2 J/m2 x s, but was less efficient when the dose rate was increased by a factor of 2.5 to 0.5 J/m2 x s. It is suggested that solar-UV radiation would not influence the cell growth of P. tetraurelia for the reason of high PR activity even when the ozone concentration was decreased 30% from the present levels.     

TEMPORAL CHANGES IN SURFACE ULTRAVIOLET RADIATION: A STUDY OF THE ROBERTSON-BERGER METER AND DOBSON DATA RECORDS

Abstract— Ultraviolet radiation data sets obtained by Robertson-Berger meters located at Bismarck, ND and Tallahassee, FL show variations over the time period 1974–1985 which we interpret in terms of clouds and ozone. Cloudiness is a major source of variance in the irradiance measurements. When this variance is minimized, the monthly mean Robertson-Berger meter record contains trends which are in good agreement with irradiance calculations based on the Dobson ozone measurements in spring, summer and early autumn. Despite the agreement among trends, predictions based on the ozone data explain 40% or less of the variance in the monthly mean radiation values over the 11-year period. The radiation measurements contain negative trends in winter which are contrary to expectations based on the behavior of ozone alone. These trends remain when we minimize the effects of cloudiness. Based on the information available in this study, it is not possible to determine whether the wintertime trends have an instrumental or environmental origin.     

Sensitivity of erythemally effective UV irradiance and daily exposure to temporal variability in total ozone

The provision of information to the public about current levels of the erythemally effective UV radiation is an important issue in health care. The quality of promoted values is therefore of special importance. The atmospheric parameter which affects the erythemally effective UV radiation under clear sky most is the total ozone content of the atmosphere. In this paper we examined the sensitivity of the erythemally effective irradiance and daily radiant exposure to the temporal variability of total ozone on time scales from 1 to 15 days. The results show that the sensitivity is highest for the first 24 h. Larger time scales do not exhibit a similar influence. Total ozone measurements of the previous day may already cause uncertainties higher than 0.5 UV index (UVI) independent of the geolocation. For comparison, a temporal persistence of 15 days may cause uncertainties of 1.2 UVI at 50°N, 1 UVI at 30°S and less than 1 UVI at the equator. The results of this study allow finding the necessary temporal resolution of total ozone values when a certain accuracy for the UVI or for the purpose of sun protection is required. The results are compared with those of two preceding studies where we quantified the influence of measurement uncertainties and spatial total ozone variability to the erythemally effective irradiance at noon and to the daily dose. We conclude that temporal variability of total ozone is the most critical issue, but also measurement uncertainties do have a noticeable influence on the erythemally effective radiation.     

ANNUAL EXPOSURES TO CARCINOGENIC RADIATION FROM THE SUN AT DIFFERENT LATITUDES and AMPLIFICATION FACTORS RELATED TO OZONE DEPLETION. THE USE OF DIFFERENT GEOMETRICAL REPRESENTATIONS OF THE SKIN SURFACE RECEIVING THE ULTRAVIOLET RADIATION

In most calculations of annual fluences of carcinogenic light as well as of the radiation amplification factor and of biological amplification factors associated with ozone depletions, the radiation is assumed to fall on a horizontally oriented plane surface. This is obviously a bad approximation of the surface of the human body. In order to evaluate the importance of using a realistic geometric representation of the surface of the human body we here present calculations of the flux of carcinogenically effective radiation falling on three different bodies: a vertically standing cylinder, a sphere and a horizontally oriented surface. The exposure to carcinogenic radiation depends strongly on the surface geometry. However we find that the radiation amplification factors are almost independent of the surface geometry chosen. The biological amplification factors for the three geometrical representations are also similar to within 20%. The total amplification factor for the increase in the incidence of non-melanoma skin cancer related to ozone depletion is about 17% larger when a cylindrical representation is used compared to when a plane horizontal surface is considered.     

Effects of relative humidity and CO(g) on the O3-initiated oxidation reaction of Hg0(g): kinetic & product studies

Ozone is assumed to be the predominant tropospheric oxidant of gaseous elemental mercury (Hg0(g)), defining mercury global atmospheric lifetime. In this study we have examined the effects of two atmospherically relevant polar compounds, H2O(g) and CO(g), on the absolute rate coefficient of the O3-initiated oxidation of Hg0(g), at 296 +/- 2 K using gas chromatography coupled to mass spectrometry (GC-MS). In CO-added experiments, we observed a significant increase in the reaction rate that could be explained by pure gas-phase chemistry. In contrast, we found the apparent rate constant, k(net), varied with the surface-to-volume ratio (0.6 to 5.5 L flasks) in water-added experiments. We have observed small increases in k(net) for nonzero relative humidity, RH < 100%, but substantial increase at RH > or = 100%. Product studies were performed using mass spectrometry and high resolution transmission electron microscopy coupled to an electron dispersive spectrometer (HRTEM-EDS). Our results give evidence for enhanced chain growth of HgO(s) on a carbon grid at RH = 50%. A water/surface/ozone independent ozone oxidation rate is estimated to be (6.2 +/- (1.1; tsigma/ radicaln) x 10(-19) cm3 molecule(-1) s(-1). The total uncertainty associated with the ensemble of experiments amount to approximately < or = 20%. The atmospheric implications of our results and the effect of an added reaction partner in homogeneous and heterogeneous atmospheric chemistry will be discussed.     

大气臭氧化学研究进展

臭氧是大气化学中的核心物种。在平流层中,臭氧层可以吸收对生物有害的紫外辐射,对地球生命起保护伞作用。在对流层大气中,适量臭氧对清洁大气是有益的。但是,由于对流层中臭氧前体物排放量的增加,特别是在大城市,产生的高浓度臭氧会对大气环境造成严重污染,对人类、动植物和生态环境具有极大危害。臭氧的研究一般结合外场观测、实验室烟雾箱模拟和计算机数值模拟进行。深入开展大气臭氧化学研究,不仅有助于全面深入理解大气氧化过程以及全面掌握区域乃至全球大气自净能力,而且能为对流层污染控制提供科学依据和方案。本文总结了近年来有关臭氧化学的研究进展,论述了臭氧问题与人类当前面临的一些主要环境问题间的相互关系;重点综述了近年来有关南极臭氧空洞、中纬度地区臭氧低值和北极地区臭氧的损耗机理及其发展趋势;综述了臭氧与大气光化学和气溶胶间的耦合关系,并结合我国实际情况,提出了大气臭氧化学尚待深入开展研究的一些重要科学问题。     

PENETRATION OF UV-B AND BIOLOGICALLY EFFECTIVE DOSE-RATES IN NATURAL WATERS*

Abstract— Spectral irradiance measurements. from 310 to 650 nm. have been made in low and modcrately productive ocean waters. These new data and selected earlier clear ocean water data are used as a basis for extrapolating the diffuse attenuation coefficient for irradiance into the 280 nm region. This allows a quantitative calculation of the penetration of UV-B (280–340 nm) and of biologically (DNA) effective dose-rates as a function of depth into various ocean water types. The model of Green et al. (1974a) for various atmospheric ozone thicknesses has been used to obtain input surface irrddiancc for this calculation. Our purpose is to provide a basis for estimating the penetration of possible increased UV-B into natural waters due to possible changes in the ozone concentration of the stratosphere. Given appropriate biological data, this method allows a quantitative evaluation of radiation effects on aquatic organisms as a function of depth. As a specific example, our results have been graphically compared with the dosage-response results on anchovy larvae obtained by Hunter et al. (1978).     

Phytochemicals for prevention of solar ultraviolet radiation-induced damages

While solar light is indispensable for sustenance of life, excessive exposure can cause several skin-related disorders. The UV part of solar radiation, in particular, is linked to disorders ranging from mild inflammatory effects of the skin to as serious as causing several different types of cancers. Changes in lifestyle together with depletion in the atmospheric ozone layer during the last few decades have led to an increase in the incidence of skin cancer. Skin cancers consisting of basal and squamous cell carcinomas are especially linked to the UVB part of solar radiation. Reducing excessive exposure to solar radiation is desirable; however, as this approach is unavoidable, it is suggested that other novel strategies be developed to reduce the effects of solar radiation to skin. One approach to reduce the harmful effects of solar radiation is through the use of phytochemicals, an approach that is popularly known as "Photochemoprotection." In recent years many phytochemicals with potential antioxidant properties have been identified and found to be photoprotective in nature. We describe here some of the most popular phytochemicals being studied that have the potential to reduce the harmful effects associated with solar UV radiation.     

Future UV radiation in Central Europe modelled from ozone scenarios

Photobiologically and photochemically relevant UV radiation for the time around the years 2015 and 2050 is estimated by radiative transfer calculations using variable ozone content based on model simulations. The future cloud conditions are assumed unchanged. Assuming various emission scenarios of chlorfluorohydrocarbons (CFCs) and other trace gases, and taking into account future temperature development and changing atmospheric dynamic conditions, ozone values are simulated. On the basis of these data, three different scenarios of the future total ozone content over Central Europe are analysed, which represent from current knowledge, probable as well as optimistic (high ozone and low UV irradiance) and pessimistic (low ozone and high UV irradiance) conditions. According to these scenarios the future development of the UV radiation is expected not to follow the increasing trend of UV irradiation observed during the last three decades. The predicted changes are highly variable with season. During late winter and spring, the enhanced recent UV values will persist for the next decades. Till 2015 a further slight increase is predicted for springtime. In contrast, during summer and fall, the UV level is assumed to remain on the recent level. For 2050 a decrease to values close to that of an anthropogeneous nearly undisturbed ozone chemistry, as it was found around 1970, is predicted. In addition to average long-time variations of the UV irradiance, short-time increase may occur due to ozone minihole events or due to a large volcanic eruption. The latter can produce a marked increase in UV radiation for several months. During ozone minihole events, with maximum occurrence in spring, UV irradiance is typically increased for a few days. Such episodes must be taken into account additionally to the average UV development. They will occur also in the future and result in UV radiation increases against undisturbed conditions, which are similar to present minihole events. These differences are much larger than the average changes predicted for future ozone development.     

Actinic effects of light and biological implications

Illumination is not the only, nor even the most important, benefit of the earth's complement of solar optical radiation; life itself is physically and chemically balanced between effects of too much and too little of it. Chemically, the effects range from the synthesis of ozone in the stratosphere and biochemicals in the biosphere, to the influence or control of complete living organisms, including humans. This actinism depends upon the spectrum, irradiancc and modulation, or SIAM. of the natural optical radiation environment. By manipulating the SIAM of artificially produced actinic optical radiation, profound effects are now routinely induced in people, animals and plants. The next logical application for this SIAM technology is in the environments where people themselves live and work. Meanwhile, it should be recognized that artificial illumination, as presently prescribed for these environments, is actinic.     

ULTRAVIOLET RADIATION IN ANTARCTICA: INHIBITION OF PRIMARY PRODUCTION

With the seasonal formation of the ozone hole over Antarctica, there is much concern regarding the effects of increased solar UV-B radiation (280–320 nm) on the marine ecosystem in the Southern Ocean. In situ incubations of natural phytoplankton assemblages in antarctic waters indicate that under normal ozone conditions UV-B radiation is responsible for a loss of approximately 4.9% of primary production in the euphotic zone, whereas UV radiation with wavelengths between 320 and 360 nm causes a loss of approximately 6.2%. When combined with data on the action spectrum for photoinhibition by UV radiation, our data suggest that the enhanced fluence of UV-B radiation under a well-developed ozone hole (150 Dobson units) would decrease daily primary productivity by an additional amount of 3.8%. Calculations that take into consideration the extent and duration of low stratospheric ozone concentrations during September to November indicate that the decrease in total annual primary production in antarctic waters due to enhanced UV-B radiation would be 0.20%.     

Radiation-Chemical Formation of Ozone in an Oxygen-Containing Gas Atmosphere

The process of ozone formation in an oxygen-containing gas atmosphere by the action of ionizing radiation was studied. A kinetic model of the process was constructed for the O₂–N₂ system. The effects of the main parameters of radiolysis on the O₃ formation rate were analyzed. The atmospheric emission of ozone from industrial-scale power units that employ electron-beam flue gas cleaning of harmful impurities was evaluated from the standpoint of its conceivable favorable effect on the Earth ozone layer.     

The effect of humidity on the ozonolysis of unsaturated compounds in aerosol particles

Atmospheric aerosol particles are important in many atmospheric processes such as: light scattering, light absorption, and cloud formation. Oxidation reactions continuously change the chemical composition of aerosol particles, especially the organic mass component, which is often the dominant fraction. These ageing processes are poorly understood but are known to significantly affect the cloud formation potential of aerosol particles. In this study we investigate the effect of humidity and ozone on the chemical composition of two model organic aerosol systems: oleic acid and arachidonic acid. These two acids are also compared to maleic acid an aerosol system we have previously studied using the same techniques. The role of relative humidity in the oxidation scheme of the three carboxylic acids is very compound specific. Relative humidity was observed to have a major influence on the oxidation scheme of maleic acid and arachidonic acid, whereas no dependence was observed for the oxidation of oleic acid. In both, maleic acid and arachidonic acid, an evaporation of volatile oxidation products could only be observed when the particle was exposed to high relative humidities. The particle phase has a strong effect on the particle processing and the effect of water on the oxidation processes. Oleic acid is liquid under all conditions at room temperature (dry or elevated humidity, pure or oxidized particle). Thus ozone can easily diffuse into the bulk of the particle irrespective of the oxidation conditions. In addition, water does not influence the oxidation reactions of oleic acid particles, which is partly explained by the structure of oxidation intermediates. The low water solubility of oleic acid and its ozonolysis products limits the effect of water. This is very different for maleic and arachidonic acid, which change their phase from liquid to solid upon oxidation or upon changes in humidity. In a solid particle the reactions of ozone and water with the organic particle are restricted to the particle surface and hence different regimes of reactivity are dictated by particle phase. The potential relevance of these three model systems to mimic ambient atmospheric processes is discussed.     

IMPACT OF ENHANCED SIMULATED SOLAR ULTRAVIOLET RADIATION UPON A MARINE COMMUNITY

Abstract—There is evidence to indicate that an increased exposure to solar radiation in the UV-B region (specifically, 290–320 nm) may occur as a result of anthropogenic degradation of stratospheric ozone. The fact that present levels of solar UV radiation can detrimentally affect marine organisms led to experiments to quantify the impact of increased UV radiation upon a marine community. Two 720–l seawater chambers (continuous flow-through design) were exposed to simulated solar UV radiation. Fluorescent sunlamps filtered by a 290 nm cutoff filter (a 0.13 mm thickness of cellulose triacetate film) were used as the radiation source. Utilization of three different weighting factors for the spectral irradiances at the surface of the chambers yielded differences of 18%, 35% and 40% in biologically effective fluence rate between the two chambers. Analysis of attached forms of algae at various depths demonstrated that a surface exposure of 1.4W/m² in the 290–315nm waveband as contrasted with the chamber receiving a surface exposure of 1.0W/m² resulted in depressed Chl a concentrations, reduced biomass, increased autotrophic indices, and decreased community diversity. These results indicate a potential for adverse effects of increased solar UV-8 radiation: decreased community diversity, community structure shifts, and decreased productivity.     

Simulation of ozone depletion using ambient irradiance supplemented with UV lamps

In studies of the biological effects of UV radiation, ozone depletion can be mimicked by performing the study under ambient conditions and adding radiation with UV-B lamps. We evaluated this methodology at three different locations along a latitudinal gradient: Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (Argentina). Experiments of the effect of potential ozone depletion on marine ecosystems were carried out in large outdoor enclosures (mesocosms). In all locations we simulated irradiances corresponding to 60% ozone depletion, which may produce a 130-1900% increase in 305 nm irradiance at noon, depending on site and season. Supplementation with a fixed percentage of ambient irradiance provides a better simulation of irradiance increase due to ozone depletion than supplementation with a fixed irradiance value, particularly near sunrise and sunset or under cloudy skies. Calculations performed for Ushuaia showed that, on very cloudy days, supplementation by the square-wave method may produce unrealistic irradiances. Differences between the spectra of the calculated supplementing irradiance and the lamp for a given site and date will be a function of the time of day and may become more or less pronounced according to the biological weighting function of the effect under study.     

Daily duration of vitamin D synthesis in human skin with relation to latitude, total ozone, altitude, ground cover, aerosols and cloud thickness

Vitamin D production in human skin occurs only when incident UV radiation exceeds a certain threshold. From simulations of UV irradiances worldwide and throughout the year, we have studied the dependency of the extent and duration of cutaneous vitamin D production in terms of latitude, time, total ozone, clouds, aerosols, surface reflectivity and altitude. For clear atmospheric conditions, no cutaneous vitamin D production occurs at 51 degrees latitude and higher during some periods of the year. At 70 degrees latitude, vitamin D synthesis can be absent for 5 months. Clouds, aerosols and thick ozone events reduce the duration of vitamin D synthesis considerably, and can suppress vitamin D synthesis completely even at the equator. A web page allowing the computation of the duration of cutaneous vitamin D production worldwide throughout the year, for various atmospheric and surface conditions, is available on the Internet at http://zardoz.nilu.no/~olaeng/fastrt/VitD.html and http://zardoz.nilu.no/~olaeng/fastrt/VitD-ez.html. The computational methodology is outlined here.     

Parameterization of daily solar global ultraviolet irradiation

Daily values of solar global ultraviolet (UV) B and UVA irradiation as well as erythemal irradiation have been parameterized to be estimated from pyranometer measurements of daily global and diffuse irradiation as well as from atmospheric column ozone. Data recorded at the Meteorological Observatory Potsdam (52 degrees N, 107 m asl) in Germany over the time period 1997-2000 have been used to derive sets of regression coefficients. The validation of the method against independent data sets of measured UV irradiation shows that the parameterization provides a gain of information for UVB, UVA and erythemal irradiation referring to their averages. A comparison between parameterized daily UV irradiation and independent values of UV irradiation measured at a mountain station in southern Germany (Meteorological Observatory Hohenpeissenberg at 48 degrees N, 977 m asl) indicates that the parameterization also holds even under completely different climatic conditions. On a long-term average (1953-2000), parameterized annual UV irradiation values are 15% and 21% higher for UVA and UVB, respectively, at Hohenpeissenberg than they are at Potsdam. Daily global and diffuse irradiation measured at 28 weather stations of the Deutscher Wetterdienst German Radiation Network and grid values of column ozone from the EPTOMS satellite experiment served as inputs to calculate the estimates of the spatial distribution of daily and annual values of UV irradiation across Germany. Using daily values of global and diffuse irradiation recorded at Potsdam since 1937 as well as atmospheric column ozone measured since 1964 at the same site, estimates of daily and annual UV irradiation have been derived for this site over the period from 1937 through 2000, which include the effects of changes in cloudiness, in aerosols and, at least for the period of ozone measurements from 1964 to 2000, in atmospheric ozone. It is shown that the extremely low ozone values observed mainly after the eruption of Mt. Pinatubo in 1991 have substantially enhanced UVB irradiation in the first half of the 1990s. According to the measurements and calculations, the nonlinear long-term changes observed between 1968 and 2000 amount to +4%, ..., +5% for annual global irradiation and UVA irradiation mainly because of changing cloudiness and + 14%, ..., +15% for UVB and erythemal irradiation because of both changing cloudiness and decreasing column ozone. At the mountain site, Hohenpeissenberg, measured global irradiation and parameterized UVA irradiation decreased during the same time period by -3%, ..., -4%, probably because of the enhanced occurrence and increasing optical thickness of clouds, whereas UVB and erythemal irradiation derived by the parameterization have increased by +3%, ..., +4% because of the combined effect of clouds and decreasing ozone. The parameterizations described here should be applicable to other regions with similar atmospheric and geographic conditions, whereas for regions with significantly different climatic conditions, such as high mountainous areas and arctic or tropical regions, the representativeness of the regression coefficients would have to be approved. It is emphasized here that parameterizations, as the one described in this article, cannot replace measurements of solar UV radiation, but they can use existing measurements of solar global and diffuse radiation as well as data on atmospheric ozone to provide estimates of UV irradiation in regions and over time periods for which UV measurements are not available.