Limiting Stratospheric Ozone Depletion

As mentioned in Chapter 6, Section 6.2, stratospheric ozone, O3, serves as a shield against harmful ultraviolet radiation from the sun. Threats to this essential shield, especially from CFC compounds released into the atmosphere, were discussed in Chapter 7, Section 7.9. This section discusses measures being taken to protect stratospheric ozone, especially with the development of substitutes for CFCs that are much less likely to harm stratospheric ozone. 

What is the Gaia hypothesis or theory What does it have to do with sustaining the atmosphere Who first proposed this hypothesis and for what discovery related to sustaining the atmosphere is this scientist noted  

Black carbon is a term that is applied both to a material in the atmosphere and to a material commonly found in the geosphere (soil). Explain how black carbon in or carried by the atmosphere may contribute to global warming. How does the production of black carbon that ends up in soil (biochar) tend to reduce global warming  

What is meant by the concept of the Anthropocene and how is it related to sustainability of the atmosphere Who is commonly credited with coining the term Anthropocene and with which other major environmental issue is this person commonly associated  

What is carbon capture and how is it used to reduce atmospheric warming What are some specific examples of the practice of carbon capture What are the best places to put captured carbon and why is it not such a good idea to pump it deep into oceans  

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In this paper I will describe some aspects of important environmental problems from the point of view of the chemical reactions that occur in the atmosphere. An overview of the processes involved in stratospheric ozone depletion is given in the papers by Professor Rowland and Professor Anderson, in acid precipitation by Dr. Phillips, and in tropospheric photochemistry by Professor Chameides. It is not practical for me to discuss the details of all of these complicated systems, so I will concentrate on a few issues which are of current interest to me and which I believe touch on some of the key uncertainties in our understanding of the environmental problems. I will also limit my discussion to gas phase reactions, although we know that many liquid phase or heterogeneous reactions are taking place, especially in the troposphere. 

A third approach is the sensitivity coefficient method in which gradients of c, (/ kj c,o) with respect to c/o and A, are calculated and employed to evaluate the multidimensional integrals. Ehhalt et al. (1979) used this method to place uncertainty limits on the predictions of stratospheric ozone depletion. To calculate the sensitivity coefficients, Ehhalt et al. (1979) made small perturbations in the variables c,o and k, one at a time, and applied fi-... 

When the impact of process scale is viewed from the planetary boundaries perspective, the inherent multicriteria nature of any sustainability assessment is indispensable. Even when only environmental LCA impacts are accounted for, studies have shown that certain boundaries have been crossed or are very close to the limit (i.e., with respect to climate change, biodiversity loss, and nitrogen and phosphorous cycles), while others are stiU reasonably well safeguarded (i.e., stratospheric ozone depletion, ocean acidification, and freshwater use) [64]. It is therefore possible that different production sectors may have an impact on different planetary boundaries some of which may be within or already outside their safe operating space. For instance, studies have indicated the severe impacts of plastic debris on marine organisms [65]. Thus, from a cradle-to-grave LCA perspective, fossil-based plastics production may have a more direct or at least a different kind of effect in terms of biodiversity compared to fossil-based fuel production, which is certainly in higher production scales. 

It now appears that both the extreme magnitude and geographic limitations of the Antarctic ozone depletion are due to meteorologic patterns peculiar to the South Polar regions. The large decrease beyond the small reduction in the rest of the stratosphere apparently involves the circulation of the polar vortex, a complex interaction of Cl with oxides of nitrogen, their physical trapping in extremely cold (T < — 80°C) clouds and preferential removal of some species by precipitation. 

It is important to understand the sources and loss mechanisms of stratospheric sulfate aerosols. These aerosols are linked to the decrease in ozone at mid-latitudes because they hydrolyse N2O5, reducing the amount of NOx that would otherwise limit the efficiency of chlorine-catalysed ozone depletion. In addition these aerosols scatter light, cooling the planet [127]. Their concentration increases dramatically following major volcanic eruptions however they are always present at background levels. The source of these background aerosols is a matter of debate. In 1976 Paul Crutzen presented the idea that sulfate aerosols result from the photolysis of carbonyl sulphide [128] ... 

It is probably true to say that the term environmental chemistry has no precise definition. It means different things to different people. We are not about to offer a new definition. It is clear that environmental chemists are playing their part in the big environmental issues—stratospheric ozone (C) () depletion, global warming and the like. Similarly, the role of environmental chemistry in regional-scale and local problems—for example, the effects of acid rain or contamination of water resources—is well established. This brief discussion illustrates the clear link in our minds between environmental chemistry and human beings. For many people, environmental chemistry is implicitly linked to pollution . We hope this book demonstrates that such a view is limited and shows that environmental chemistry has a much wider scope. 

The first step in the production of ozone, the photolysis of molecular oxygen [reaction (1)], is rate limiting. While ozone production is slow, there are chemical reactions that can rapidly destroy it. One of the major species that is efficient in the removal of ozone is chlorine. The role of chlorine species in the depletion of ozone has been investigated actively since 1974, when Rowland and Molina [2] drew attention to the potential impact of human-made materials known as chlorofluorocarbons (CFCs) on ozone produced in the stratosphere. Chlorofluorocarbons are widely used in our daily life as refrigerants, aerosol propellants, cleaning solvents, and in fire-extinguishing applications. CFCs are stable, chemically inert, and have low toxicity. These properties make CFCs ideal for many applications and account for their wide use. However, the release of chlorine from the photodissociation of chlorofluorocarbons poses a central threat to ozone produced in the stratosphere ... 

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