The fate of nitrogen upon nitrite irradiation: Formation of dissolved vs. gas-phase species

Nitrite photochemical transformation is an important sink for nitrite and a source of nitric oxide, which affects the air-water partitioning of (NO)-N-center dot. It is shown here that aliphatic and aromatic (OH)-O-center dot scavengers alter the photochemical fate of nitrogen, in addition to enhancing nitrite photodegradation. In aerated solution, the addition of phenol as scavenger induced a significant formation of gas-phase nitrogen species from irradiated nitrite, differently from nitrite alone or in the presence of 2-propanol. Moreover, phenol strongly favoured the photochemical production of gas-phase nitric oxide in aerated solution: an upper limit of about 20% could be established for the nitrite fraction that may be transformed into gas-phase (NO)-N-center dot under these conditions. The photochemical production of (NO)-N-center dot was considerably higher in the absence of oxygen, most likely because the scavenging of nitric oxide by superoxide is an important (NO)-N-center dot sink in aerated systems. These results suggest that the concentration of dissolved oxygen and the nature of the (OH)-O-center dot scavenger(s) may considerably affect the phototransformation of nitrite into gas-phase nitrogen compounds, and particularly into nitric oxide, in aqueous solution and at water-air interfaces. (C) 2015 Elsevier B.V. All rights reserved.