Ozone-forming constituents

Reductions of volatile organic compounds (VOCs) which are ozone-forming constituents, must only be met in the summertime. However, the emission requirements for air toxics applies year-round. The definition of air toxics includes benzene, 1,3 butadiene, polycyclic organic matter (POM), formaldehyde and acetaldehyde. 

Depletion of the Ozone Layer. As a constituent of the atmosphere, ozone forms a protective screen by absorbing radiation of wavelengths between 200 and 300 nm, which can damage DNA and be harmful to life. Consequently, a decrease in the stratospheric ozone concentration results in an increase in the uv radiation reaching the earth s surfaces, thus adversely affecting the climate as well as plant and animal life. Pot example, the incidence of skin cancer is related to the amount of exposure to uv radiation. 

As a constituent of the atmosphere, ozone forms a protective screen by absorbing radiation of wavelengths between 200 and 300 nm, which can... 

The photochemical production of ozone is of limited industrial interest because the practical yield is much lower than that produced by silent electric discharge. However, there are a number of scientific problems connected with photochemical ozone production which have not yet been solved, and the number continually increases, because of the important role which ozone plays in the atmosphere. As a constituent of the atmosphere (about 100 millionth parts thereof at the earth s surface), ozone forms a protective screen because it absorbs radiations of wave lengths below 3000 A. which are deleterious to life. Furthermore, the heat liberated by such absorption and by the exothermic decomposition of ozone creates in the higher atmosphere (at approximately 40 km.) a warm layer which helps to establish thermal equilibrium on our planet. 

Nitric oxide, NO, results from high-temperature combustion, both in stationary sources such as power plants or industrial plants in the production of process heat and in internal combustion engines in vehicles. The NO is oxidized in the atmosphere, usually rather slowly, or more rapidly if there is ozone present, to nitrogen dioxide, NO2. NO2 also reacts further with other constituents, forming nitrates, which is also in fine parhculate form. 

OZONE A reactive form of oxygen the molecule of which contains 3 atoms of oxygen. In the ozone layer it protects the earth by filtering out ultra-violet rays. At ground level, as a constituent of photochemical smog, it is an imtant and can cause breathing difficulties. 

In order to calculate the steady-state concentration of ozone in the stratosphere, we need to balance the rate of production of odd oxygen with its rate of destruction. Chapman originally thought that the destruction was due to the reaction O + 03 —> 2O2, but we now know that this pathway is a minor sink compared to the catalytic destruction of 03 by the trace species OH, NO, and Cl. The former two of these are natural constituents of the atmosphere, formed primarily in the photodissociation of water or nitric oxide, respectively. The Cl atoms are produced as the result of manmade chlorofluorocarbons, which are photodissociated by sunlight in the stratosphere to produce free chlorine atoms. It was Rowland and Molina who proposed in 1974 that the reactions Cl + 03 —> CIO + O2 followed by CIO + O —> Cl + O2 could act to reduce the concentration of stratospheric ozone.10 The net result of ah of these catalytic reactions is 2O3 — 3O2. 

All these rapidly reacting intermediates are potentially harmful to the cell and might play a role in ozone toxicity. Furthermore, the potential for ozone-induced free-radical chain reactions exists. It appears likely that more than one radical is formed, either directly from ozone or as a result of the interaction of ozone with normal cellular constituents. 

C6Hg03, Mr 128.13, is a constituent of pineapple and strawberry aroma and is also found in other foods. It forms colorless crystals (mp 77-79 °C) with a relatively weak, nonspecific odor. Dilute solutions develop a pineapple, strawberry-like odor. It can be prepared by cyclization of hexane-2,5-diol-3,4-dione in the presence of an acidic catalyst [186]. The dione is the ozonization product of 2,5-hexynediol, which is obtained by ethynylation of acetaldehyde. 

The photochemical processes of triatomic molecules have been extensively studied in recent years, particularly those of water, carbon dioxide, nitrous oxide, nitrogen dioxide, ozone, and sulfur dioxide, as they are important minor constituents of the earth s atmosphere. (Probably more than 200 papers on ozone photolysis alone have been published in the last decade.) Carbon dioxide is the major component of the Mars and Venus atmospheres. The primary photofragments produced and their subsequent reactions are well understood for the above-mentioned six triatomic molecules as the photodissociation involves only two bonds to be ruptured and two fragments formed in various electronic states. The photochemical processes of these six molecules are discussed in detail in the following sections. They illustrate how the knowledge of primary products and their subsequent reactions have aided in interpreting the results obtained by the traditional end product analysis and quantum yield measurements. 

The Chapman mechanism. The mechanism of ozone formation and destruction in the stratosphere was first formulated by Chapman (205) in 1930. He did not consider the effects of minor constituents and physical transport processes that have since been recognized as important factors to explain the discrepancy between the calculated results and the actual observation. According to his mechanism, ozone is formed by the photolysis... 

Oxygen has two allotropes, the normal dioxygen 02 form and ozone 03(1) formed by subjecting 02, to an electric discharge. Ozone is a trace constituent of the atmosphere, where it plays an important role as an absorber of UV radiation. 

Ozone is an important natural constituent of the atmosphere,21 being principally concentrated (up to 27% by weight) between altitudes of 15 and 25 km. It is formed by solar uv radiation in the range 240 to 300 nm via the reactions... 

Ozone is a natural constituent of the upper atmosphere trace amounts naturally exist in the lower atmosphere. Formation of 03 in the upper atmosphere occurs in steps, i.e., a molecule of oxygen being split into atomic oxygen and the resulting atomic oxygen reacting with another oxygen molecule to form ozone ... 

Pathway 1 (eq 6a) shows no oxygen-atom transfer and the production of r, as discussed for the H202 reaction (eq 3). The I+ can form a variety of products, in particular I2 from excess T as discussed for the H202 reaction. The [I-03] intermediate should break down to oxygen and hydroxide on H20 and anion attack. The reaction of ozone with iodide to form I2 is quantitative in the presence of excess T and can be used for the analysis of ozone (43). In seawater this process seems less likely to occur because I" is a trace constituent. 

The main constituents of NOM in natural water are humic substances consisting of humic and fulvic acids. Humic substances are the precursors of THMs. These must be degraded before chlorine disinfection because once THMs are formed they cannot be removed by chemical oxidation. Ozonation can degrade humic substances into low molecular weight compounds that are less reactive toward chlorine, and hence can minimize the formation of... 

Ozone (O3), a major constituent of smog, is a health hazard at ground level. In the stratosphere, however, a layer of ozone shields the Earth from harmful solar radiation. The greatest concentration of ozone occurs between 12 and 15 miles above the Earth s surface. The ozone layer is thinnest at the equator and densest towards the poles. Ozone is formed in the atmosphere from the interaction of molecular oxygen with very short wavelength ultraviolet light. 

Photolysis of O3 in the Hartley bands leads to 02( Ag) production, with 60% formed vibrationally excited,and under atmospheric conditions quenching is found to be a rapid process. Rates of formation of 02( Ag) by this mechanism in the upper atmosphere of Venus have been calculated and compared with those determined by observations of the 02( Ag) emission at 1.27 pm for the values to agree, the previously accepted ozone concentrations would have to be revised upwards by a factor of 10. In the terrestrial atmosphere, the photolysis of 1 6q 1 8q at wavelengths between 170—205 nm could be an important source of odd oxygen in the high stratosphere and mesosphere, as solar radiation not absorbed by discrete 02 features may penetrate these regions and photolyse the minor isotopic constituent (present as 4% of naturally occurring 02). ... 

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