Autoxidation of sulphur dioxide in the presence of alcohols under conditions related to the tropospheric aqueous phase

In this work attempts were made to elucidate the monoterpenic alcohol inhibition of the S(IV) autoxidation by comparing the inhibiting activity of cis-verbenol (C10H15OH), myrtenol (C10H15OH) and nopol (C11H17OH) with that of ethanol (C2H5OH) and 2-propanol (C3H7OH). Results of laboratory experiments on the kinetics of S(IV) autoxidation in the presence of these alcohols were interpreted using the equation derived by Alyea and Bäckström (J. Am. Chem. Soc. 51 (1929) 90), brought into relationship with the actual mechanistic knowledge on the reactivity of the inhibitors with respect to sulphate radicals. The rate constants for the reaction: alc+SO4•−(+O2)→SO42−+H++HO2+ald involving cis-verbenol and myrtenol have been determined as equal to, respectively, 5.4×109 and 4.2×109 M−1 s−1. These results were obtained under the assumption that the main chain termination is due to simultaneous scavenging SO5•− radical anions by FeII and SO4•− radical anions by an alcohol. In the case of nopol the rough estimate gave for the rate constant of the latter reaction a value of 9.0×109 M−1 s−1 burdened with an error caused by the sulphoxy radical induced autoxidation of nopol. The studied airborne compounds of biological origin were shown to be potentially significant modifiers of the acidity formation in clouds and a sink for sulphoxy radicals participating in further transformations of these compounds.