, Volume 61, Issue 1, pp 31-55
Date: 05 Jun 2009

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

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This is the first study, which shows both NH3 and NH 4 + 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:

$$ R_{aut} ={{R_0 } \mathord{\left/ {\vphantom {{R_0 } {\left( {{\text{1 + }}B\left[ {\text{Inh}} \right]_{\text{T}} } \right)}}} \right. } {\left( {{\text{1 + }}B\left[ {\text{Inh}} \right]_{\text{T}} } \right)}} $$
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 NH 4 + . Both ammonia and ammonium ions appear to inhibit the autoxidation either by scavenging SO 4 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.