Ozone threats

Power Plants—Scientist Labels New Ozone Threats , Newark Star Ledger, Newark, NY, 17 (Nov 15, 1975)... 

Recognition of the threat of stratospheric ozone depletion posed by chlorofluorocarbons and chloro-fltiorohydrocarbons led 131 countries to sign the Montreal Protocol in 1987. Production of chlorofluorocarbons was banned as of January 1, 1996, because of their potential to further deplete stratospheric ozone. Chlorofluorohydrocarboiis will be... 

The haloalkanes (also called alkyl halides) are alkanes in which at least one hydrogen atom has been replaced by a halogen atom. Although they have important uses, many haloalkanes are highly toxic and a threat to the environment. The haloalkane 1,2-dichlorofluoroethane, CHC1FCH2C1, is an example of a chlorofluorocarbon (CFC), one of the compounds held responsible for the depletion of the ozone layer (see Box 13.3). Many pesticides are aromatic compounds with several halogen atoms. 

Meanwhile, Crutzen had done experiments showing that ozone in the upper atmosphere can be destroyed easily by reactions with nitrogen oxides. This work demonstrated that the ozone layer is in a delicate balance that could be disturbed significantly by changes in atmospheric composition. In 1974, Molina and Rowland combined Crutzen s experimental work with their own theoretical analysis and published a prediction (hypothesis) that CFCs pose a serious threat to the ozone layer. 

We see that chiorine atoms provide an aitemative mechanism for the reaction of ozone with oxygen atoms. The iower-energy pathway breaks down ozone in the stratosphere at a significantiy faster rate than in the absence of the cataiyst. This disturbs the deiicate baiance among ozone, oxygen atoms, and oxygen molecules in a way that poses a serious threat to the iife-protecting ozone iayer. 

A vast library waits to be read on ozone depletion. The best book by far is Topic study 1 the threat to stratospheric ozone in the Physical Chemistry Principles of Chemical Change series, published in the UK by the Open University, Milton Keynes, 1996. From the UK s Royal Society of Chemistry come Climate Change, Royal Society of Chemistry, Cambridge, 2001, Green Chemistry, M. Lancaster, Royal Society... 

The full text of the 1985 Vienna Convention for the Protection of the Ozone Layer is available at http //www.unep.org/ozone/vienna t.shtml, and contains much of the primary data that alerted the scientific community to the threats of CFCs, etc. It is somewhat dated now, but the Web page of the United Nations Ozone Secretariat is more reliable http //www.unep.org/ozone/index-en.shtml. 

There is a vaiiety of problems associated with air pollution, starting from photochemical smog, ozone formation, and acid rain at a regional level, to the greenhouse effect and ozone-layer depletion at a global level. These problems have an adverse impact on both environment and public health (Table 1.1) the last two problems are a threat to life on Earth generally. 

The residence times of SO2 and H2S04 in the troposphere are typically only a few days, but sulfuric acid aerosols reaching the stratosphere can be very persistent together with nitric acid, they provide the solid surfaces in polar stratospheric clouds on which reaction 8.9 and related processes occur heterogeneously. Indeed, studies suggest that NOx emissions of commercial supersonic aircraft in the lower stratosphere may pose less of a threat to the ozone layer than previously supposed however, the accompanying formation of sulfuric and nitric acid aerosols may exacerbate ozone loss by increasing the available catalytic surface area. 

In the early 1970s, Mario Molina (b. 1943) of the Massachusetts Institute of Technology, F. Sherwood Rowland (b. 1927) of the University of California, Irvine, and Paul J. Crutzen (b. 1933) of the Max Planck Institute in Germany, all shown in Figure 17.16, recognized the potential threat to stratospheric ozone posed by chlorofluorocarbons (CFCs). Because CFCs are inert gases, they were once commonly used in air conditioners and aerosol propellants. Two of the most frequently used CFCs are shown in Figure 17.17. 

Two cases have been considered as a possible threat to human healtli > a result of the partial destruction of ozone in the stratosphere (1) injection of NO into the stratosphere by SSTs (supersonic transports) and of H< i by the space shuttle and (2) release of chlorofluoromethanes into the in. posphere. 

Many large water treatment chemical service companies have entered the ozone marketplace, primarily in response to customer inquiries, and have linked up with ozone equipment manufacturers in one way or another. For some service companies, these moves have probably been more of a way of being in contact with ozone market developments and warding off any real threat to their core business, rather than positively embracing the technology. 

A group of compounds were discovered in the 1930s and were called the chlorofluorocarbons (CFCs). Because of their inertness they found many uses, especially as a propellant in aerosol cans. CFC-12 or dichlorodifluoromethane, CF2C12, was one of the most popular CFCs in use in aerosols. Scientists believe that CFCs released from aerosols are destroying the ozone layer and steps are being taken to reduce this threat. 

In this volume of Issues we address the sources, environmental cycles, uptake, consequences and control of many of the more important chlorinated organic micropollutants. Under this heading we have included a range of semi-volatile persistent compounds, notably polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) as well as a number of chlorinated pesticides. We have not sought to include volatile species such as CFCs which cause environmental problems of an entirely different nature. The compounds included in this volume cause no threat to the stratospheric ozone layer, but have given widespread cause for concern in relation to their environmental persistence and high toxicity, and their potential for adverse effects on humans and wildlife. 

With reduced ozone levels, more ultraviolet radiation from the Sun reaches Earth. Among humans, UV-induced skin cancer and eye damage are becoming a serious threat. The increased levels of radiation also damage phytoplankton in fresh and marine ecosystems. Since phytoplankton are the base of the aquatic food chain, this damage affects all other water species. As you learned earlier, the presence of ozone close to Earth damages crops and forests. A lack of ozone in the atmosphere, however, also reduces the yield of crops, such as barley and canola, and harms forests. 

Fully halogenated CFCs were eliminated in polystyrene foam food packaging and containers. Substitute blowing agents used are either no threat to the ozone or are a 95% improvement over fully halogenated CFCs. Action has been taken such as where PS foam cups now are 100% CFC-free, etc. 

Molina and Rowland [82] were the first to recognize the threat of the released chlorine to the stratospheric ozone layer. The threat originates from the catalytic cycle ... 

As we mentioned before, substituted methanes with the general formula CFxCl4. x containing both chlorine and fluorine as substituents are called chlo-rofluorocarbons (CFCs) and are also known as Freons. These substances are very unreactive and have been extensively used as coolant fluids in refrigerators and air conditioners. Unfortunately, their chemical inertness allows Freons to remain in the atmosphere so long that they eventually reach altitudes where they are a threat to the protective ozone layer (see Section 15.9), and the use of these compounds is being rapidly phased out. 

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