Photochemical processes involving nitrite in surface water samples

A study into nitrite photochemistry was carried out on surface (both lake and river) water samples. In the tested samples, nitrite photolysis accounted for 0-60% of •OH photoproduction, nitrate for 0-40%, and dissolved organic matter (DOM) photochemistry played on average the main role. In real surface waters, an effect of radiation extinction by the water column would also be observed, and is expected to inhibit nitrate photochemistry at a higher extent compared to nitrite or DOM. Nitrite showed a definite time evolution with irradiation. Photodegradation prevailed in samples with the highest initial concentrations, while photogeneration with DOM transformation was evident in the presence of undetectable initial nitrite levels. Nitrite also accounted for up to 9% of •OH scavenging, which would produce up to 66% of photoformed nitrogen dioxide. The remaining percentage of nitrogen dioxide generation is accounted for by nitrate photolysis. Photogenerated nitrogen dioxide could then be involved in significant processes of aromatic nitration, in particular in the transformation of phenol into nitrophenols.