Nitrate Radical Cannot Initiate Oxidation of Hg(0) to Hg(II) in the Laboratory or at Ground Level in the Atmosphere

Nitrate radical (NO3) has been suggested to participate in oxidizing gaseous Hg(0) in the atmosphere, most convincingly in the field study by Peleg et al. (Environ. Sci. Technol. 2015, 49, 14008-14018). This conclusion has been hard to reconcile with the two step mechanism of Hg(0) conversion to Hg(II) via Hg(I), due to the low value reported for the NO3-Hg(I) bond energy (5.0 kcal mol 1). We use a high level of computational chemistry to refine this , we find this bond energy to be 6.5 kcal mol-1, and we use standard statistical mechanics to compute the equilibrium constant, Kc(T) for NO3 + Hg(0) = NO3Hg(I). Our kinetic analysis finds, that under the conditions of Peleg et al., NO3 could not have contributed significantly to the formation of Hg(II). In addition, we find that the one experimental kinetic study of this reaction would not have been able to measure the rate constant.