Ozone potential

Interest in the effects of ozone on alveolar macrophages has been spurred by the observation that relatively low concentrations of ozone potentiate respiratory infections in animals and perhaps man. Coffin et al ob-ser a decrease in the number of bacteria phagocytized by alveolar macrophages obtained from rabbits exposed to various concentrations of ozone as low as 0.3 ppm. Some suggestion of a lack of threshold is present, but it is not clear whether the difference from the controls at lower ozone concentrations is statistically significant. 

Ozone might interfere with the intracellular bactericidal capabilities of alveolar macrophages by inactivating lysosomal hydrolases, or perhaps through the destruction of heme-containing enzymes that are apparentiy involved in producing superoxide anion radical. Further evaluation of the process by which relatively low concentrations of ozone potentiate bacterial infection would be of value. 

Black, F., S. Tejada, and M. Gurevich, Alternative Fuel Motor Vehicle Tailpipe, and Evaporative Emissions Composition and Ozone Potential, J. Air Waste Manage. Assoc., 48, 578-591 (1998). 

However, together with other chlorinated compounds like PCBs and CFCs, it possesses noxious effects on environment, particularly a high ozone potential depletion. It was, in fact, classified in the IV group among CFCs and so its use was banned, in developed countries, from 1996. 

Earth s atmosphere contains a region of increased ozone concentration, commonly known as the ozone layer. In recent decades, pollutants have contributed to the destruction of ozone, potentially reducing the ozone layer s ability to protect life on Earth from harmful radiation. 

Disinfeetion. Chlorine, as gaseous chlorine or as the h5rpochlorite ion, is widely used as a disinfectant. However, its use in some cases can lead to the formation of toxic organic chlorides, and the discharge of excess chlorine can be harmful. Ozone as an alternative disinfectant leads to products that have a lower toxic potential. Treatment is enhanced by ultraviolet light. Indeed, disinfection can be achieved by ultravifflet light on its own. 

More precisely, the rate of ozone formation depends closely on the chemical nature of the hydrocarbons present in the atmosphere. A reactivity scale has been proposed by Lowi and Carter (1990) and is largely utilized today in ozone prediction models. Thus the values indicated in Table 5.26 express the potential ozone formation as O3 formed per gram of organic material initially present. The most reactive compounds are light olefins, cycloparaffins, substituted aromatic hydrocarbons notably the xylenes, formaldehyde and acetaldehyde. Inversely, normal or substituted paraffins. 

Ozone is very much more reactive than oxygen and is a powerful oxidising agent especially in acid solution (the redox potential varies with conditions but can be as high as + 2.0 V). Some examples are 1. the conversion of black lead(ll) sulphide to white lead(II) sulphate (an example of oxidation by addition of oxygen) ... 

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. 

Compound CAS Registry Number Relative ozone depletion 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). 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

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. 

Typically, ozone cracking initiates at sites of high stress (flaws) on the mbber surface. Thus, in general, mbber articles should be designed to rninirnize potential sites of high elongation such as raised lettering. Similarly, the use of clean molds helps to reduce the incidence of surface flaws. 

Heterogeneous chemistry occurring on polar stratospheric cloud particles of ice and nitric acid trihydrate has been estabUshed as a dorninant factor in the aggravated seasonal depletion of o2one observed to occur over Antarctica. Preliminary attempts have been made to parameterize this chemistry and incorporate it in models to study ozone depletion over the poles (91) as well as the potential role of sulfate particles throughout the stratosphere (92). 

Trichloroethylene is being evaluated by the industry as a precursor in the production of hydrochlorofluorocarbons (HCEC), the replacement products for the chlorofluorocarbons impHcated in the depletion of the stratospheric ozone. At this time it is too early to project any estimates or probabihties for potential volume changes as a result of this opportunity (23). 

If in an ozone nonattainment area, does the toller facility actually emit, or have the potential to emit, VOC or NOx in excess of the threshold limit value ... 

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