Reference #: MAD-1017-699205
Submit Date: 04/01/2002 16:06:50-0500

Confounding influences of aerosols and clouds on surface UV radiation

ABSTRACT:
Atmospheric particles (aerosols and clouds) alter the ultraviolet (UV) radiation environment by scattering and sometimes absorbing incoming solar photons. The amounts of aerosol and cloud are highly variable both spatially and temporally, and both are subject to changes induced by human activities, e.g. pollution and global warming. Sensitivity studies with radiative transfer models illustrate a range of complex effects due to the presence of aerosol and/or clouds. Surface UV irradiances are usually reduced, but in some circumstances enhancements are also possible (e.g. with broken clouds, or for exposures of non-horizontal surfaces). These effects are very sensitive to wavelength and to the presence of absorbing compounds (e.g. soot, organics). Two case studies of anthropogenic influence will be discussed: (1) Measured and calculated changes in local surface UV radiation due to aerosols in heavily polluted urban areas; and (2) future global changes in UV radiation climatology, due to changes in cloudiness associated with climate warming (as calculated with a general circulation model). In both cases, the UV changes are of the order of magnitude (but opposite sign) of those estimated to have already occurred due to recent stratospheric ozone depletion.

Keywords: Ultraviolet, climate, aerosols, clouds

Reference #: KRI-1018-537579
Submit Date: 04/10/2002 10:07:59-0500

New measures of photoprotection

ABSTRACT:
A decrease in the concentration of stratospheric ozone results in an increase in the amount of solar UVB (280-320nm) radiation that reaches the surface of the earth. Although UVB is involved in the formation of Vitamin D in skin and thus has beneficial effects on human health, excessive exposure to UVB contributes to skin cancer formation, skin aging, cataract formation, and potentially harmful effects on the immune system. Although, solar UV radiation is the major cause of human skin cancer, different types of skin cancer may be related to UV exposure in different ways. Of the three most common types of skin cancer, squamous cell carcinoma seems to have the most direct relationship to UVB radiation, in that the risk of developing this type of skin cancer is directly related to cumulative, lifetime exposure to solar UVB radiation. Basal cell carcinoma is also directly related to UVB exposure, but for melanoma, the skin cancer with the most lethal behavior, the picture is not so clear. Studies in a fish model indicated that UVA, as well as UVB, could lead to melanoma formation. Even though there is as yet no direct evidence that UVA exposure contributes to melanoma formation in humans, these findings have raised the possibility that ozone depletion, which affects only UVB radiation, might not affect the incidence of melanoma. Studies in other animal models and improved understanding of the molecular mechanisms of melanoma carcinogenesis are needed to resolve this important question. Exposing the skin to UVB can prevent certain immune responses and can even lead to a long-lasting state of specific immune suppression. These immunosuppressive effects of UVB radiation contribute to skin cancer formation. Moreover, in animal models, UVB irradiation has been shown to interfere with host resistance to infectious agents. These findings have raised the concern that increased UVB radiation could increase the prevalence and severity of infectious certain diseases in humans, as well as reduce the effectiveness of vaccinations. However, epidemiological or experimental evidence supporting this possibility is still lacking. Thus, increased UVB radiation is expected to increase the incidence of some skin cancers and cataract, but its impact on the incidence of and mortality from melanoma and infectious diseases remains to be determined.

Keywords: UVB

Reference #: 074556
Submit Date:

Break

ABSTRACT:

Keywords:

Reference #: NUN-1017-896276
Submit Date: 04/03/2002 22:28:21-0500

Modelling the impacts of UV radiation on microbial communities in Antarctic coastal waters

ABSTRACT:
The effect of ambient solar UV radiation on the species composition and concentration of natural protist assemblages from Antarctic coastal waters was determined. Subsamples of the community were exposed to UV radiation attenuated to equivalent water column depths of 1.0, 2.0, 3.0, 3.6 and equal to or greater than 20 metres for periods of between 8 hrs and 1 week. The carbon concentration attributable to phytoplankton, protozoa and bacteria was then calculated and the effect of UV irradiance modelled in relation to the erythemal UV dose and dose rate. Model results argue that all three microbial communities respond to UV stress, but are affected mainly by dose rates rather than dose. Furthermore, stress effects cease below erythema irradiance values of 29 mW m-2. As exposure time increases there is a shift in microbial population from phytoplankton to protozoa. Increased UVB radiation in Antarctica as a result stratospheric ozone depletion is likely to reduce primary production and increase microbial respiration in near surface waters, reducing carbon flux to deep waters.

Keywords: ultraviolet radiation, antarctic coastal waters, microbial communities, ozone depletion

Reference #: WUE-1017-958917
Submit Date: 04/04/2002 15:58:18-0500

Interaction of climate change with ozone depletion, and implications for

ABSTRACT:
Worldwide compliance with the international agreements to protect ozone is resulting in significant reductions in the emissions of the CFCs, Halons and other halocarbons which have the largest effects on ozone. As a result, levels of stratospheric ozone should slowly begin to recover over the coming decades as reactive chlorine and bromine in the stratosphere decline. This recovery will be gradual, primarily because of the long time it takes for CFCs and Halons to be removed from the atmosphere. However, projected changes in climate and changes in the concentrations of greenhouse gases, like methane and nitrous oxide, are likely to significantly impact the recovery of ozone. A number of the existing analyses of the ozone recovery are based on the chlorine and bromine available to affect ozone, and do not account for climate change and other factors that may affect future trends in ozone, such as the emissions of other gases and aerosols. In those studies, ozone gradually recovers, to reach levels comparable to those in 1980, before extensive ozone destruction began in Antarctica and elsewhere, by 2040-2050. The limited number of modeling studies that do consider other changes occurring in the global atmosphere suggest that the recovery may take much longer, with some suggesting a recovery may not occur over the next century. As organizations around the world consider rulings to slow down the rate of climate change, it will be important to understand the effects of these rulings on the recovery of ozone. For example, reducing the amount of climate change due to greenhouse gases and aerosols could reduce the cooling of the stratosphere and thus reduce the time it takes for ozone to recover. This paper examines the state of knowledge of the interactions between climate change and ozone recovery.

Keywords: climate change, ozone recovery, stratospheric ozone, greenhouse gases

Reference #: MCE-1018-538695
Submit Date: 04/11/2002 10:05:53-0500

Effects of Human Activity on Atmospheric Ozone and the Transmission of Ultraviolet Radiation

ABSTRACT:
The paper will discuss current understanding of the factors that combine to regulate the abundance of ozone in the stratosphere and that determine thus the flux of solar ultraviolet radiation reaching the Earths surface. It will address specifically the subtle factors that link changes in ozone with changes in climate. In particular, it will suggest that changes in climate anticipated for the near future as a consequence of the build-up of greenhouses gases (the so-called global warming issue) are likely to exacerbate losses of ozone expected to occur in polar regions in spring. The future course of ozone depends not only on the fate of chlorine and bromine but is sensitive also to levels of nitrous oxide, methane and the state of the climate system.

Keywords: ozone, climate