Radicals source, nitrite photolysis

The concept that free radicals are important intermediates in photochemical and other redox interactions of oxygen, organic compounds and heavy metals in natural waters has received considerable support recently ((1-3) and references therein this volume). Some of the major primary radicals expected are hydroxyl (OH), superoxide (02 ). and various organic moieties (R, RO, ROO). Of these, OH is of interest because of its extremely high reactivity, significant formation rate from a known source (nitrite photolysis, among others) and the analogy of its known key role in tropospheric chemistry. 

Atkinson, R W. P. L. Carter, A. M. Winer, and J. N. Pitts, Jr., An Experimental Protocol for the Determination of OH Radical Rate Constants with Organics Using Methyl Nitrite Photolysis as an OH Radical Source, J. Air Pollut. Control Assoc., 31, 1090-1092 (1981). 

Cu11 complexes undergo photoreduction to the Cu1 species and may be the photocatalyst in photo-oxidation cycles of organic environmental matter, quite similar to the Fem species [20, 81] (see Figure 9.11). Dissolved copper compounds are important to transformation reactions, because they react with hydroperoxyl (H02) and superoxide (02 ) radicals much faster than other species present in the solution. Oxidation of Cu1 and Fe11 by H202 is a source of the OH radicals in oceans comparable with nitrite photolysis, whereas photochemistry of Cu11 chlorocom-plexes provides Cl radicals [81] ... 

Zafiriou, O. C., and True, M. B. (1979). Nitrite photolysis as a source of free radicals in productive surface waters. Geophys. Res. Lett. 6(2), 81—84. 

Alkyl halides (RX X = Cl, I) are an important source of halogens in the atmosphere. The major tropospheric sinks of these compounds are photolysis (RBr, RI) and reaction with OH radicals. In the case of alkyl iodides (RI) relative kinetic studies of their OH reactions in photoreactors are complicated by fast reactions with the 0( P) atoms generated by the photochemical OH radical sources. Figure 1 below shows a In-ln plot of the kinetic data from an experiment performed in a large photoreactor to determine the OH rate coefficient for the reaction OH + CH3CH2CH2I relative to OH + ethene using the photolysis of methyl nitrite (CH3ONO) as the OH radical source. A recent example of the implementation of the relative kinetic technique for the determination of OH radical rate coefficients in a photoreactor can be found in Olariu et al. (2000). 

Nitrite photolysis as radical source 28,933 Nitrites s. Alkyl nitrite... 

Estimate the near-surface hydroxyl radical steady-state concentration at noon ([HO ] s (noon)) and averaged over a day ([HO ] s(24 h)) in Greifensee (47.5°N) on a clear summer day. Assume that photolysis of nitrate (NOj) and nitrite (NOj) are the major sources, and that DOM, HCOj, and CO are the major sinks for HO in Greifensee. The concentrations of the various species are given in the margin. 

Excimer laser photolysis of ethyl nitrite was studied at 248 and 351 nm as a function of O2 pressure (Zellner). In contrast to methyl nitrite, the photolysis produced not only C2H5O radicals but also methyl radicals with high yield. This study indicates that photolysis of higher alkyl nitrites is not an appropriate source for the laboratory generation of alkoxy radicals. 

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