Enhancement by anthraquinone-2-sulphonate of the photonitration of phenol by nitrite: Implication for the photoproduction of nitrogen dioxide by coloured dissolved organic matter in surface waters

Anthraquinone-2-sulphonate (AQ2S) under UVA irradiation is able to oxidise nitrite to NO2 and to induce the nitration of phenol. The process involves the very fast reactions of the excited triplet state 3AQ2S* and its 520-nm absorbing exciplex with water, at different time scales (ns and μs, respectively). Quinones are ubiquitous components of coloured dissolved organic matter (CDOM) in surface waters and AQ2S was adopted here as a proxy of CDOM. Using a recently developed model of surface-water photochemistry, we found that the oxidation of nitrite to NO2 by 3CDOM* could be an important NO2 source in water bodies with high [NO2-] to [NO3-] ratio, for elevated values of column depth and NPOC.