Ozone photochemical decomposition

Most chlorofluorocarbons are hydrolytically stable, CCI2F2 being considerably more stable than either CCl F or CHCI2F. Chlorofluoromethanes and ethanes disproportionate in the presence of aluminum chloride. For example, CCl F and CCI2F2 give CCIF and CCl CHCIF2 disproportionates to CHF and CHCl. The carbon—chlorine bond in most chlorofluorocarbons can be homolyticaHy cleaved under photolytic conditions (185—225 nm) to give chlorine radicals. This photochemical decomposition is the basis of the prediction that chlorofluorocarbons that reach the upper atmosphere deplete the earth s ozone shield. 

It would be of great interest to know whether the photochemical decomposition of ozone proceeds by the mechanism... 

CA 50, 12482 (1956) (Flame propagation in ozone) 29)Sax (1957), 161-61 (Destruction of expls) 30)F.C.Ikle, "The Social Impact of Bomb Destruction , Univ of Oklahoma Press, Norman, Okla (1958) 3l)Anon, Ordnance Service in the Field , US Army Field Manual FM 9-1 (1959) (Destruction of ammo) 32)Anon, Ordnance Ammunition Service , FM 9 5 (1959) (Destruction of ammo) 33)A.B.Amster, "Relationship Between Decomposition Kinetics and Sensitivity (U), Stanford Research Institute, Menlo Park, California,Repts (1962), Contract No Nonr 3760(00) (Conf, not used as a source of info) 34)P.W.M.Jacobs A.R.T.Kureishy, Kinetics of Thermal and Photochemical Decomposition of Some Alkali Metal Azides , Imperial College, London, England, Final Tech Rept (1964) Contract DA-91-591-EUC-2059 34a)Anon, Care, Handling, Preservation and Destruction of Ammunition , TM 9-1300-206 (1961) 35)-Anon, Investigations of the Mech-... 

The rate of the gas phase decomposition of ozone has been studied by many investigators under a wide range of conditions, yet no completely satisfactory mechanism has ever been proposed for either the thermal or photochemical decompositions. 

The photochemical decomposition of ozone has long been cited as an example of one of the few systems in which it is necessary to propose an energy chain mechanism. This came about from the observation that at very short wave lengths quantum yields as high as 6 were observed (10), whereas the primary photochemical process... 

The carbon-chlorine bond in most chlorofluorocarbons can be homolytically cleaved under photolytic conditions (185-225 nm) to give chlorine radicals. This photochemical decomposition is the basis of the prediction that chlorofluorocarbons that reach the upper atmosphere deplete the earth s ozone shield. 

The oxygen atoms in Equation (17.5) are supplied by the photochemical decomposition of molecular oxygen and ozone described earlier. Note that the Cl atom plays the role of a catalyst in the reaction mechanism scheme represented by Equations (17.4) and (17.5) because it is not used up and therefore can take part in many such reactions. One Cl atom can destroy up to 100,000 O3 molecules before it is removed by some other reaction. The CIO species is an intermediate because it is produced in the first elementary step [Equation (17.4)] and consumed in the second step [Equation (17.5)]. The above mechanism for the destruction of ozone has been supported by the detection of CIO in the stratosphere in recent years (Eigure 17.7). As can be seen, the concentration of O3 decreases in regions that have high amounts of CIO. 

Castellano, E., and H. J. Schumacher, (1962b). Photochemical decomposition of ozone in yellow-red light and the mechanism of its thermal decomposition. J. Chem. Phys. 36, 2238. 

The percentage of stratospheric non-radical bromine species is lower than that of chlorine because the slower speed of this reaction and because of the efficiency of the photochemical decomposition. For this reason, stratospheric bromine is more efficient in destroying ozone than is chlorine. The estimated factor is from 40 to 50, but the concentration of active bromine species is much less than chlorine species. 

In the primary step, polymers may be attacked by molecular oxygen, ozone, or already available free radicals. New free radicals are formed, especially by thermal or photochemical decomposition of primarily formed hydroperoxides ... 

The oxygen atoms in Equation (17.5) are supplied by the photochemical decomposition of molecular oxygen and ozone described earlier. Note that the Cl atom plays the role of a catalyst in the reaction mechanism scheme represented by Equations (17.4) and (17.5) because it is not used up and therefore can take part in many such reactions. One... 

The main purpose of this chapter is to survi atmospheric concentrations of photochemical oxidants, with emphasis on surface concentrations and the distribution patterns associated with them. The reason for that em> phasis is that the photochemical oxidants that affect public health and welfare are largely concentrated in this region. The whole subject of stratospheric ozone (and its filtering of ultraviolet light and interactions with supersonic-transport exhaust products), nuclear weapon reaction products, and halogenated hydrocarbon decomposition pr ucts is not treated here. 

Another simple reaction with a complicated reaction rate law is Reaction 1-5, 203(gas) 302(gas), which may be accomplished thermally or by photochemical means. The reaction rate law for the thermal decomposition of ozone is d /df= c5[03] /[02] when [O2] is very high, and is d /dt=ks [O3] when [O2] is low. 

Photochemical production and decomposition of ozone, and the ozone hole... 

Ozone in the atmosphere is a good example of photochemical reactions. Atmospheric ozone is not due to equilibrium. The production and decomposition of ozone are largely by photochemical process, and the concentration of ozone in the stratosphere is at steady state, controlled by the kinetics of photochemical production and decomposition. 

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