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: 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.