Dl. Sedlak et J. Hoigne, OXIDATION OF S(IV) IN ATMOSPHERIC WATER BY PHOTOOXIDANTS AND IRON IN THE PRESENCE OF COPPER, Environmental science & technology, 28(11), 1994, pp. 1898-1906
We have simulated some of the reactions that result in oxidation of S(
IV) and production of secondary photooxidants in cloud droplets, using
gamma-radiation to generate hydroperoxyl (HO2), superoxide (O-2(-)),
and hydroxyl (OH.) radicals in oxygenated, formate-containing solution
s. In the absence of transition metals, HO2/O-2(-) undergoes dispropor
tionation to form hydrogen peroxide (H2O2). S(IV) oxidation can be acc
ounted for entirely by reactions with H2O2 and OH. in such systems, an
d contrary to earlier reports, the oxidation of S (IV) by HO2/O-2(-) i
s unimportant. In solutions containing dissolved Fe, oxidation of S(IV
) also occurs through Fe(III)-catalyzed reactions with O-2. However, a
t the low concentrations of Cu (5-100 nM) typically measured in cloud
droplets, Fe-catalyzed oxidation of S(IV) by O-2 is inhibited through
the reduction of FeOH2+ by Cu(I), which is produced by the reduction o
f Cu2+ by HO2/O-2(-).