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A continuous radiolysis has been used for the kinetic study of the radical driven bisulfite oxidation in oxygenated and N20-02 saturated solutions. The initiation rates and initial bisulfite concentrations were varied over the ranges (3 x 10-1°)-(3 x lo-,) M s-l and 10-,-(3 x M, respectively. For oxygenated and N20-02 saturated solutions the long chain length bisulfite oxidation with the rate determining propagation reaction SO5-+ HSO3-(k) was observed at low initiation rates. The measurement of the peroxydisulfate formation rates has shown that the main t e d n a t i o n step in an N20-02 saturated solution is the reaction S05-+ SOS--S20s2-+ 0 2 (k7b) and in oxygenated solution is the reaction S05-+ H02 (klo). The rate constants ks =(3.6 f 0.5) x lo3 and k10 = (5 f 1) x lo7 M-' have been derived. The upper limit of the initiation reaction between of hydroperoxyl radical and bisulfite H02 + HS03-has been estimated as 20 M-' s-l, IntroductionThe free-radical mechanism of bisulfite autoxidation in acid solutions is important for an improved understanding of the acidification of atmospheric droplets'-8 by the emission of SO2 for an improved understanding of the chemistry of flue-gas scrubber's chemical processes9 and so on. For the first time the chain autoxidation of sulfite ion has been observed by Backstrom.Io Later the direct observations of oxysulfur radicals, so3-, s04-, and SOS-, involved in the chain mechanism of S(IV) oxidation, have been reported."-I6 It was found that the rate constants of the propagation reactions of so,-with 0 2 and SO,-with HS03-are veryThe peroxymonosulfate radical is considered as a chain carrier determining the oxidation rate of bisulfite ion, because the propagation reaction so5-+ HS03-is S~O W .~, '~ Therefore, the rate of chain oxidation of bisulfite critically depends on an absolute values of the rate constants of SO5-radical termination reactions. The high concentration of hydroperoxyl radicals in the atmosphere and thereof high solubility require the determination of the termination reaction (SO5-+ HOz) rate constant. In particular, the predominant role of the termination reaction SO5-+ 0 2 -(H02) has been demonstrated for sulfite photo~xidation'~ and for bisulfite oxidation under the action of ionizing radiation.I8 However, the rate constants of these reactions are unknown. The hydroperoxyl radicals may also play a role in the chain initiation by the reaction with bisulfite, H02 + HSO,-, but the available data are scanty and di~crepant.'~-*~ Since the considered reactions of the oxysulfur and hydroperoxyl radicals are of such importance in the autoxidation of S(IV), we have determined the rate constants of the reactions: propagation reaction of SO5-radicals with HSO3-, termination reaction SO5-+ HO2, and initiation reaction of HO2 radicals with HSO3-. Both continuous electron beam irradiation and y-irradiation of the bisulfite solutions have been employed for radical production and a kinetic study of bisulfite oxidation. BackgroundThe peroxymonosulfate and hydroperoxyl radica...

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