Ozone breakdown

The absorbance value now recorded is the amount of ozone absorbed by the system between the sample and reference cuvettes. Most of this is due to breakdown of ozone in the alkaline solution contained in the reaction vessel. If this solution is replaced by 1 N NaOH, absorbance at this point is much higher when the solution is 0,1 N HCl, absorbance is very low. This corresponds with the known rate of ozone breakdown as a function of pH ( 9 ), If linolenic acid (Sigma chemical, 99% pure, C18 3 (9c, 12c,... 

The concentration of ozone taken up by the media containing linolenic acid is plotted against time after addition in Figure 8. The rate of ozone breakdown is constant (ozone uptake linear with time) for the first two min until about 0.12 ml ozone are absorbed and then the rate decreases sharply, reaching a steady-state rate of ozone uptake between 10-12 min. This first break in the curve corresponds to an ozone uptake of 0.12 ml + (24 moles/liter) = 0.005 millimoles (or 10 M). This is equivalent to 1 mole of linolenic acid added per mole ozone absorbed. Thiobarbituric acid reactant production is also plotted on the same axis. This compound (TBA reactant) probably arises by formation of a three-carbon fragment (malondialdehyde) from the ozone-induced oxidation of linolenic acid (23). The rate of TBA reactant formation is also linear for the first 2 min at which point the curve undergoes a less pronounced break. Malondialdehyde formation ceases immediately when the ozone is shut off (Scrub 1 on). An oxygen control sample produced no malondialdehyde. 

CFCs do not decompose in the lower atmosphere. Photodecomposition occurs in the stratosphere via absorption of uv radiation and subsequent release of atomic chlo -rine which can catalyze ozone breakdown. CFC-ozone depletion hypothesis M J. Molina, F. S. Rowland, Nature 249, 810 (1974). Reviews focusing on atmospheric chemistry of CFCs, uses, potential hydrogen-substituted replace-... 

Atmospheres polluted by oxidising agents, e.g. ozone, chlorine, peroxide, etc. whose great destructive power is in direct proportion to the temperature, are also encountered. Sulphuric acid, formed by sulphur dioxide pollution, will accelerate the breakdown of paint, particularly oil-based films. Paint media resistant both to acids, depending on concentration and temperature, and oxidation include those containing bitumen, acrylic resins, chlorinated or cyclised rubber, epoxy and polyurethane/coal tar combinations, phenolic resins and p.v.c. 

The chlorine atoms in the upper atmosphere come from the breakdown of CF2 CI2 and other similar chlorofluorocarbons (CFCs), known commercially as Freons. Production of these compounds was more than one million tons in 1988, largely for use in relrigerators and air conditioners. Once released into the atmosphere, CFCs diffuse slowly upward in the atmosphere until they reach the ozone layer. There, ultraviolet light Irom the sun splits off chlorine atoms. These react with ozone, with dramatic results. Annual ozone decreases have exceeded 50% above Antarctica. The background photo shows the Antarctic hole (red-violet) on September 24, 2003. 

A luminous discharge resulting from air breakdown in the vicinity of high voltage cables. Corona produces ozone (from the oxygen in the air) and may result in rapid deterioration of the cable insulation and other unsaturated mbber in the vicinity. 

Air breakdown due to coronal discharges around high-voltage transmission lines has been considered as a possible rural source of ozone. Several investigations suggested that this cannot be a significant source. 

More recently, B. Goldstein and McDonagh demonstrated that the native protein fluorescence (280-nm excitation, 330-nm emission) of red-cell membranes exposed in vitro to ozone at 1 ppm was a somewhat more sensitive indicator of ozone effect than other characteristics measured in the same em, including oxidation of cell-membrane sulfhydiyl groups, loss of acetylcholinesterase activity, and formation of lipid peroxide breakdown products. 

Dowell et al. reported an increase in the osmotic fragility of alveolar macrophage preparations obtained horn rabbits acutely exposed to ozone at 10 ppm for 3 h or intermittently exposed to ozone at 2 ppm for 8 h/day for 7 days. Similar intermittent exposure to ozone at 0.5 ppm was without effect. A test for malonaldehyde formation was negative, but this lipid peroxide breakdown product may have been lost during the preparatory procedure. 

If photosynthetic and respiratory changes cannot account for the increases in adenylate concentration, which system is responsible It has been reported that ADP and ATP concentrations of Ehrlich ascites tirnior cells increase in the presence of adenine (15), Whether this wo ild hold true for plant cells is not known, but it seems plausible that equilibrium shifts would initiate similar responses. An increase in adenine concentrations could occur if there was any breakdown of nucleic acids. There is one report that the number of ribosomes in the chloroplast does decrease in response to ozone (16). An increase in synthesis of purines is also possible but there is no evidence to either support or refute this hypothesis. 

Most cleavable surfactants contain a hydrolyzable bond. Chemical hydrolysis is either acid- or alkaU-catalyzed and many papers discuss the surfactant breakdown in terms of either of these mechanisms, hi the environment, bonds susceptible to hydrolysis are often degraded by enzymatic catalysis, but only few papers dealing with cleavable surfactants have dealt with such processes in vitro. Other approaches that have been taken include incorporation of a bond that can be destroyed by UV irradiation or use of a bond which is cleaved when exposed to ozone. 

The reaction mechanism shown for ozone depletion includes chorine. Chlorine in this reaction acts as a catalyst. A principal source of this chlorine is from the ultraviolet breakdown of CFC (chlorofluorocar-... 

An important piece of evidence that some of this chlorine comes from the breakdown or CFCs was the unusually high levels of fluorine compounds detected in the Antarctic stratosphere. Whereas chlorine compounds come from a number of natural sources, fluorine compounds in nature are relatively rare. The source of this stratospheric fluorine, therefore, is most likely chlorofluoro-carbons. In addition to elevated fluorine levels, evidence of ozone depletion... 

In previous studies, i,e. concurrent carbonyl-oxygen exchange in the hydrolysis of esters, acid hydrolysis of orthoesters and oxidation of acetals by ozone, the configuration of the tetrahedral intermediate was determined by the application of the principle of stereoelectronic control. There could be some ambiguity in these experiments as the theory of stereoelectronic control is used to predict both the stereochemistry of the tetrahedral intermediate as well as its breakdown. The oxidation cleavage of vinyl orthoesters can therefore be considered a more powerful experimental technique in that respect because the configuration of the hemi-orthoester... 

Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of the ozone layer is due to the breakdown of certain chlorine- or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules. 

The development of chemical industry has provided us with the means to produce, on an ecologically significant scale, chemicals that interfere with the natural cycles of synthesis and breakdown either because they accelerate or slow down large-scale natural processes (e.g., the fluoro chloro hydrocarbons which accelerate the breakdown of ozone by sunlight) or, more commonly, because they resist breakdown themselves (e.g., certain synthetic polymers). This has become a matter of grave and widespread concern and has resulted in regulations and voluntary measures to restrict or prohibit the manufacture and use of materials that interfere with the natural cycles. This concern is particularly acute in those cases where this interference has direct or indirect adverse effects upon human health (as in the case of the fluoro chloro hydrocarbons), but it exists also where massive accumulation occurs without known health hazards (as in the case of the too-stable synthetic polymers). 

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