Ozone destroying potential

Perfluorinated ethers and perfluorinated tertiary amines do not contribute to the formation of ground level ozone and are exempt from VOC regulations (32). The commercial compounds discussed above have an ozone depletion potential of zero because they do not contain either chlorine or bromine which take part in catalytic cycles that destroy stratospheric ozone (33). 

International agreements (Montreal Protocol in 1987 and subsequent amendments), as well as national regulations, have strongly limited the production and the use of the CFCs. These chemical compounds have been gradually replaced by partially halogenated hydrocarbons, and specifically by hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These alternative products are relatively easily destroyed in the troposphere and hence their lifetimes are substantially shorter than those of the CFCs (typically 1-10 yrs as opposed to 10-100 yrs). The ozone depletion potential of the HCFCs is about an order of magnitude smaller than that of the fully halogenated halocarbons. HFCs are not a threat to ozone because they do not contain any chlorine or bromine atoms. 

The ozone depleting potential (ODP) is the propensity of the substance to destroy stratospheric ozone, integrated over the lifeofthecompound. By definition, ODP for CFC-11 = 1. For other CFC compounds, both the total ODP and time scale of the effect can vary (Table 3). 

The stratospheric ozone-depleting potential of a compound emitted at the Earth s surface depends on how much of it is destroyed in the troposphere before it gets to the stratosphere, the altitude at which it is broken down in the stratosphere, and chemistry subsequent to its dissociation. Halocarbons containing hydrogen in place of halogens or containing double bonds are susceptible to attack by OH in the troposphere. (We will consider the mechanisms of such reactions in Chapter 6.) The more effective the tropospheric removal processes, the less of the compound that will survive to reach the stratosphere. Once halocarbons reach the stratosphere their relative importance in ozone depletion depends on the altitude at which they are photolyzed and the distribution of halogen atoms, Cl, Br, and F, contained within the molecule. 

What were CFCs primarily used for before their potential as ozone-destroying chemicals was recognized What compounds have been used as replacements ... 

Ozone depletion potential is measured relative to CFC-11 and it represents the amount of ozone destroyed by emission of a vapor over its entire atmospheric lifetime relative to that... 

Ozone depleter Ozone depletion potential is the value relative to that of CFC-11. It represents the amount of ozone destroyed by the emission of gas over its entire atmospheric life-time. Photochemical ozone creation potential is a relative value to that of etiiene to form ozone in an urban environment. Numerous solvents belong to both groups. 

The Ozone Depletion Potential (ODP) of a compound is defined as the ratio of the total amount of ozone destroyed by a given amount of the compound to the amount of ozone destroyed by the same mass of CFC-11. 

Ozone plays a vital role in protecting life on Earth because it absorbs potentially harmful ultraviolet radiation and also helps to maintain a heat balance in the atmosphere. For a discussion of some ozone-producing and ozone-destroying reactions occurring in the atmosphere, and the impact made by human activities, go to the Focus On feature for Chapter 22, The Ozone Layer and Its Environmental Role, on the MasteringChemistry site. 

HCFC/HFCs) currently widely used in the foam industry. However, HCFCs still destroys the ozone layer (much less than CFCs). Although HFCs are considered to have an ozone depletion potential of zero, they are still greenhouse gas. The second type is hydrocarbons. Due to their high flammability and volatile nature, hydrocarbons are considered as fire hazards. The third type is inert gases, e.g. H2O, CO2, and N2. CO2 has better solubifity in polymers than the other two and supercritical state of CO2 is relatively easier to reach. In summary, in all these potential alternatives, CO2 is the most preferable because it is nonflammable, inexpensive, essentially nontoxic and environmentally friendly. ... 

In this sequence the Cl also acts as a catalyst and two molecules are destroyed. It is estimated that before the Cl is finally removed from the atmosphere in 1—2 yr by precipitation, each Cl atom will have destroyed approximately 100,000 molecules (60). The estimated O -depletion potential of some common CFCs, hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, are presented in Table 10. The O -depletion potential is defined as the ratio of the emission rate of a compound required to produce a steady-state depletion of 1% to the amount of CFC-11 required to produce the 1% depletion. The halons, bromochlorofluorocarbons or bromofluorocarbons that are widely used in fire extinguishers, are also ozone-depleting compounds. Although halon emissions, and thus the atmospheric concentrations, are much lower than the most common CFCs, halons are of concern because they are from three to ten times more destmctive to O, than the CFCs. 

The presence of naturally occurring ozone in the lower stratosphere creates a potential hazard for passengers and crew members of high flying aircraft (163,164). Ozone in the inlet air to the aircraft cabin, which can reach 1.2 ppm, is destroyed catalyticaHy. 

Global warming potential (infra-red absorption) Ozone depletion A compound s ability to absorb infra-red radiation The ability of a chemical to reach the stratosphere and interact with and destroy ozone Global warming potential (GWR) Preferred CWR less than carbon dioxide) Atmospheric lifetime... 

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