Kinetics of ammonia and ammonium ion inhibition of the atmospheric oxidation of aqueous sulfur dioxide by oxygen

This is the first study, which shows both NH3 and NH4+ to inhibit the autoxidation of aqueous SO2 in the pH range 7.0-8.5. The rate of the autoxidation, R-aut, in both buffered and unbuffered media at a fixed pH is in conformity with the rate law: R-aut = R-0/(1+B[Inh](T)) where R-0 is rate in the absence of the inhibitors, B is a pH dependent empirical constant and [Inh](T) is the analytical concentration of NH3 or NH4+. Both ammonia and ammonium ions appear to inhibit the autoxidation either by scavenging SO4- radicals or by forming less-reactive/unreactive Co(II)-NH3 complexes or both. The atmospheric relevance of the inhibition by ammonia and ammonium ions is discussed.