14 Sep : Increased UV-B Levels Shorten the Lifetime of Commercial PolymersThe outdoor service life of commercial plastics is often limited by their UV-stability and weatherability. The outdoor lifetimes of plastics, however, depend on their formulations and specifically on the type and concentration of photostabiliser additives used in them. Information on the lifetimes of unstabilised (virgin) plastic materials is therefore of limited practical value in assessing the UV stability of plastics exposed outdoors.Available data on the degradation of plastics by UV in sunlight show that for some polymers a portion of the damage is attributable to the UV-B radiation component. As any depletion of the stratospheric ozone layer would increase the UV-B content of the solar radiation reaching the Earth’s surface, it is reasonable to expect a consequent increase in the rate of degradation of plastics containing these polymers (and other materials such as wood) under these conditions. The amount by which the service life of materials will be shortened by this phenomenon will of course depend on the type of polymer, location in question, and the light-stabiliser used in the formulation. Climatic factors, particularly higher ambient temperatures due to global warming, will tend to accelerate UV-induced degradation to an extent depending on the type of plastic and on the location of exposure. These reductions in service life of plastics can probably be countered by using higher than normal concentrations of existing light stabilisers in the plastic formulation, surface protection of materials (e.g. painting wood) or by selecting different polymeric materials with better UV-resistant materials for outdoor applications. These approaches might be able to retain the service life at present-day levels but may increase the cost of relevant products.
Stratospheric Ozone Depletion Change Air Quality and Global Warming
Stratospheric ozone depletion normally increases the ozone concentration at ground level. In general the impact of stratospheric ozone depletion is smaller than that of local and regional air pollution sources. Increases in the particulates in the atmosphere related to global warming may reduce tropospheric ozone production. Modelling and field studies show that the reduction of ozone photolysis rate and ozone production in the troposphere is expected in the presence of increased amounts of absorbing aerosols in the boundary layer.
Climate change can alter air quality in many ways. Changes in temperature, winds and cloudiness can all be important. Some of these changes will also alter the impact of stratospheric ozone depletion. As an example, an increase in atmospheric CO2 concentration would accelerate photosynthesis, which might enhance the emissions of biological volatile organic compounds from forests and other natural ecological systems. Other sources of tropospheric air pollutants may be affected by global warming. It is known that local and large-scale biomass fires, such as are used for land-clearing, are rich sources of nitrogen oxides, carbon monoxide, methane, and other non-methane hydrocarbons, that can lead to enhanced tropospheric ozone production. Climate changes resulting from global warming may increase the risk of large scale forest and brush fires. The resulting particulates in the atmosphere can scatter sunlight, thus improving the efficiency of UV-B absorption of the boundary layer ozone and contributing to global warming. Illustration of the impact of tropospheric aerosols upon atmospheric chemistry. The aerosol can reduce the intensity of radiation, leading to a reduction in ozone production. Such a reduction offsets the impact of stratospheric ozone depletion
Risks of HFCs and HCFCs Breakdown On Humans and the Environment
The new hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) replacements for the chlorofluorocarbons (CFCs) are largely degraded before reaching the stratosphere. The final breakdown products are various fluorinated and chlorinated acetic acids. Some of these are rapidly broken down by microbiological activity in water, soil, and sediments. Other breakdown products such as trifluoroacetic acid (TFA) are very persistent but they are very water soluble and chemically nonreactive. Because of their properties, these breakdown products will ultimately collect in aquatic environments. They have low toxicity to aquatic organisms and are very unlikely to adversely affect human health or the environment.
HFCs and HCFCs (CF3CXYH) break down relatively rapidly to several products including the persistent substances such as trifluoroacetic acid (CF3COOH) and chlorodifluoroacetic acid (CF2ClCOOH). These are washed from the atmosphere by precipitation and reach surface waters, along with other chemicals washed from the soil. In locations where there is little or no outflow and high evaporation (seasonal wetlands, salt lakes and playas), these products are expected to increase in concentration over time. The concentrations of trifluoroacetic acid and chlorodifluoroacetic acid are expected to increase. While this may present a risk to aquatic organisms, these areas would also experience increases in concentrations of other water-soluble materials such as has already occurred. The effects of increased concentrations of these naturally occurring salts and other materials would likely be greater and more biologically significant than those of breakdown products of the HFCs and HCFCs. The results of this interaction with global climate change are judged to be of low significance, since the phytotoxicity of trifluoroacetic acid is not high. Illustration of the formation of persistent, water-soluble breakdown products of the HFCs and HCFCs (CF3-CXYH) and their movement and concentration by evaporation, along with other water-soluble salts to surface waters.
Ozone Depletion Affected by Global Warming
The interactions are complex, and not all of them are f ully understood In the past, scientists have sometimes stressed the differences between global warming and ozone depletion. Global warming is due to a build-up of gases that absorb outgoing infrared radiation, especially CO2, while ozone depletion is primarily due to a release of gases that catalytically destroy ozone. Ozone, the CFCs and their substitutes are minor greenhouse gases. Several other gases involved with the chemistry of ozone depletion are also greenhouse active. These include water vapour, methane (CH4), and nitrous oxide (N2O) that are increasing and will ultimately lead to increases in stratospheric gases that catalytically destroy ozone
There are several radiative feedback processes involved. Increases in temperature can lead to changes in cloud cover, rainfall patterns, ice accumulation, surface albedo, and ocean circulation. The direct radiative forcing from increases in UV-B that results from changes in ozone are not significant, since only a small fraction of the incoming solar energy falls within the UV-B range. However, increases in UV radiation at the Earth’s surface influence photochemical reactions in the troposphere that would affect the lifetimes of greenhouse gases. It has been suggested that changes in cloud cover can be induced by climate change.
Changes in solar output and future volcanic eruptions will influence both global warming and ozone depletion. It seems that while current ozone depletion is dominated by chlorine and bromine in the stratosphere, in the longer term (~100 years) the impact of climate change will dominate, through the effects of changes in atmospheric dynamics and chemistry. The result is that over the first half of the current century, increases in greenhouse gases may contribute to cooler stratospheric temperatures, since they act as infrared emitters in the stratosphere. This will lead to a decrease in the rate of catalytic destruction of ozone outside Polar regions.
In Polar regions however, the cooler temperatures may lead to increased polar stratospheric clouds, thus exacerbating ozone depletion. The temperature changes will lead to changes in atmospheric circulation. These changes may aid the mixing of long-lived CFCs from the troposphere to the stratosphere, which will increase their rate of photochemical destruction, again contributing to a faster recovery of ozone. Changes in polar ozone can also lead to changes in tropospheric circulation patterns, which in turn affect surface climate. The effects of global warming on UV radiation are twofold. The first effect results from changes in global warming that influence total ozone. The second effect results from climate change effects on other variables such as clouds, aerosols, and snow cover that influence UV directly.