Photochemical reaction of peroxynitrite and carbon dioxide could account for up to 15 %of carbonate radicals generation in surface waters

The carbonate radical (CO3-) is a photoinduced transient species occurring in surface waters. The carbonate radical can transform both natural compounds and xenobiotics. For instance, it can react with electron-rich substrates such as anilines, phenols and organic sulfur compounds. Here we used the APEX software to assess photochemical reactions, including the formation rates of transient species, based on water chemistry and depth, under summertime irradiation conditions. We found that the reaction between peroxynitrite and carbon dioxide is a potentially significant source of CO3- in sunlit surface waters, and could account for up to 10–15 % of the total CO3- formation. The peroxynitrite pathway to CO3- would be most significant at pH 7–8 and would be enhanced in waters with elevated nitrate and low alkalinity. Therefore, the proposed process could add to the known photochemical sources of CO3- in surface-water environments.