Volatile organic compound rate constant with

Peng, J., Wan., A. (1998) Effect of ionic strength on Henry s constants of volatile organic compounds. Chemosphere 36,2731-2740. Perry, R.A., Atkinson, R., Pitts Jr., J.N. (1976) Rate constants for the reaction of hydroxyl radicals with dichlorofluoromethane, and chloromethane over temperature range 298—423 K and with dichloromethane at 298 K. J. Chem. Phys. 64, 1618-1620. Perry, R.A., Atkinson, R., Pitts Jr., J.N. (1977) Rate constants for the reaction of OH radicals with CH2=CHF, CH2=CHC1, and CH2=CHBr over temperature range 299-426 K. J. Chem. Phys. 67, 458 162. 

Other secondary chlorine species (atomic Cl, CIO, ClOOCl etc.) have been made responsible for Arctic ozone depletion, whereas the sources of the chlorine atoms are poorly understood (Keil and Shepson 2006). The Cl atom reacts similarly to OH (e. g. in oxidation of volatile organic compounds Cai and Griffin 2006). However, the photolysis of HCl is too slow (even in the stratosphere) to provide atomic Cl. Thus, the only direct Cl source from HCl is due to its reaction with OH, but with a fairly low reaction rate constant (Rossi 2003). There are several chemical means of production of elemental Cl (and other halogens) from heterogeneous chemistry (see Chapter 5.8.2) in the troposphere the photolysis of chloroorganic is not very important, with a few exceptions (see Chapter 5.8.1). 

In addition to the uncertainties in correctly estimating reaction rate constants, we must recognize the uncertainties in the ambient atmospheric concentrations of the OH radical as a function of both time and place, since the lifetime, xOH, of a chemical is given by xOH = (kOH[OH]) 1. Present estimation methods are limited, and most cannot be used with any degree of reliabiity for organic compounds outside the classes of compounds used to develop the particular method. Further studies should be carried out to develop more direct (less empirical) methods for calculating OH radical (and N03 radical and 03) reaction rate constants. Until that time, rate constants should be experimentally measured when possible, recognizing that experimental measurements are currently difficult for low-volatility chemicals. 

Typically, easily oxidized organic compounds, such as those with double bonds (e.g., TCE, PCE, and vinyl chloride), as well as simple aromatic compounds (e.g., toluene, benzene, xylene, and phenol), are rapidly destroyed in AOP. The reported rate constants of the reactions involving benzene, toluene, ethylbenzene, styrene, and TCE with hydroxyl radicals in water are quite comparable and vary in a narrow range of 3.0 x 10 -7.8 x 10 L moU s (12). The photooxidafion rate constants for various volatile organics and their intermediates follow the following order (4,13,14) ... 

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