Ozone removal

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

Helmig, D Ozone Removal Techniques in the Sampling of Atmospheric Volatile Organic Trace Gases, Atmos. Environ., 31, 3635-3651 (1997). 

However, as discussed by Reiss et al. (1995a), separating the contribution of ozone reactions from other factors such as temperature and relative humidity, which also affect direct emissions, is difficult. For example, while the production rate of oxygenated organics is correlated with the ozone removal rate, the latter is also correlated with temperature. As a result, both reaction and increased direct emission rates due to higher temperatures may be contributing to these enhanced indoor levels. 

Morrison, G. C., W. W. Nazaroff, J. Alejandro Cano-Ruiz, A. T. Hodgson, and M. P. Modera, Indoor Air Quality Impacts of Ventilation Ducts Ozone Removal and Emissions of Volatile Organic Compounds, J. Air Waste Manage. Assoc., 48, 941-952 (1998). 

Nitrogen dioxide is about 20 to 50% of the total nitrogen oxides NO, (NO, NOz, HN03, N2Os), while CIO represents about 10 to 15% of the total chlorine species CIO, (Cl, CIO, HCI) at 25 to 30 km. Hence, the rate of ozone removal by CIO, is about equal to that by NO, if the amounts of NO, are equal to those of CIO,. According to a calculation by Turco and Whitten (981), the reduction of ozone in the stratosphere in the year 2022 with a continuous use of chlorofluoromethanes at present levels would be 7%. Rowland and Molina (843) conclude that the ozone depletion level at present is about 1%, but it would increase up to 15 to 20% ifthechlorofluoromethane injection were to continue indefinitely at the present rates. Even if release of chlorofluorocarbons were stopped after a large reduction of ozone were found, it would take 100 or more years for full recovery, since diffusion of chlorofluorocarbons to the stratosphere from the troposphere is a slow process. The only loss mechanism of chlorofluorocarbons is the photolysis in the stratosphere, production of HCI, diffusion back to the troposphere, and rainout. 

Ferrous ions -ozone removal from water [OZONE] (Vol 17)... 

Helmig, D. (1997) Ozone removal techniques in the sampling of atmospheric volatile oranic trace gases. Atmospheric Environment, 31 (21), 3636-51. 

Indoor air quality impacts of ventilation ducts ozone removal and emissions of volatile organic compounds. Journal of the Air sj Waste Management Association, 48 (10), 941-52. 

Zhao, P., Siegel, ).A. and Corsi, R.L (2007) Ozone removal by HVAC filters. Atmospheric Environment, 41 (15), 3151-60. 

Table 8 Calculated average ozone removal and addition rates according to pathway, ppbv day (upper part) and fractional contributions to overall production or destruction patyways (lower part)...

This is in good agreement with classical photochemical measurements which clearly demonstrated that the large quantum yield for ozone removal following excitation in the Hartley band was consistent with reactions of the electronically excited photofragments and subsequent chemical products (Wayne, 1969). 

The source strength for CFC induced stratospheric ozone removal is, of course, the tropopause mixing ratio for each of the CFC compounds. This must be known to extremely high precision at selected positions across the globe in order to predict steady state concentrations corresponding to a given release rate. Intensive analysis of the time dependence of these mixing ratios over at least a decade is critical in order to establish a lower limit on the atmospheric lifetime. 

Some reaction is found to occur between 0( D) atoms (produced from the photolysis of ozone at 253.7 nm and 25 C) and COCIF, as indicated by the high value of the quantum yield for ozone removal. However, no products were found (although analysis was not made for CO 2 which could be the major product), unlike the COCl 2 0( D) reaction, in which evidence was obtained for the formation of both CO and chlorine oxides [1038]. The rate constant for the reaction of COCIF with 0( D) atoms was estimated to be 2.8 times the value... 

Cloud processes have been predicted to have a significant effect on the chemistry of the clean troposphere (Lelieveld and Crutzen, 1990, 1991 Warneck, 1991, 1992). For example, the uptake of HCHO, HOz radicals, and N2Os into cloud droplets can lead to a decrease in the production of ozone. Removal of HCHO reduces the rate of gas-phase production of HOz radicals, and N205 into cloud droplets can lead to a decrease in the production of ozone. Removal of HCHO reduces the rate of gas-phase production of H02 radicals [reactions (33)—(36)1, and consequent conversion of NO to N02. Also, aqueous-phase reactions of H2C(OH)2, the hydrated form of HCHO, lead to the formation of 02, which can react with dissolved 03 to enhance the rate of transfer of 03 to the liquid phase over that based solely on physical solubility. Absorption of N2Os into... 

Figure 4. Release of CFCs boots the rate of ozone removal—i.e., it increases the strength of existing sink (Bunce, 1994), ...

The chlorine radicals are the ozone-removing agents. They react with ozone to form chlorine monoxide radicals and molecular oxygen. The chlorine monoxide radicals then react with ozone to regenerate chlorine radicals. These two propagating steps are repeated over and over, destroying a molecule of ozone in each step. It has been calculated that each chlorine atom destroys 100,000 ozone molecules ... 

Strong circumstantial evidence implicates synthetic chlorofluorocarbons as being responsible for the diminishing ozone layer. The interaction of these compounds with UV light generates chlorine radicals, which are the ozone-removing agents. 

Ozone removal by catalytic chlorine chemistry and the Chapman cycle are, therefore, roughly equal at about 40 km. 

FIGURE 5.33 Qualitative behavior of the ozone removal rate in the lower stratosphere as a function of NO level (Wennberg et al. 1994). SPADE stands for Stratospheric Photochemistry, Aerosols, and Dynamics Expedition. This is a cumulative plot the contributions of the various processes add to produce the upper curve. 

The reactions of CF3O radicals are critical toward accessing the potential impact of secondary products resulting from alternative halocarbon degradation on ozone perturbations. The potential for ozone removal by CF3O radicals was recognized by Francisco and Williams [132]. Example cycles originally pointed out are ... 

Anaerobic biodegradability of 2,4-dinitro-phenol using phenol-supplemented cultures is induced by ozone. Ozonization removes chemical oxygen demand (COD) by 80%. The ozonization product is effectively biodegraded to methane (Wang et al. 1989). 

Broida and Garvin have studied the interesting chemiluminescent properties of this reaction when traces of H atoms were also present with N( S). NO(A S+-X n) and (B II-X n) bands, as well as various systems of OH and NH were observed. Measurements of ozone concentration by absorption spectrometry showed rapid catalysis of ozone removal by a trace of hydrogen atoms the following simple cycle for chain removal of ozone was suggested ... 

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