Inhibition vs. enhancement of the nitrate-induced phototransformation of organic substrates by the *OH scavengers bicarbonate and carbonate.

Contrary to common expectations, the hydroxyl scavengers, carbonate and bicarbonate, are able to enhance the phototransformation by nitrate of a number of substituted phenols. Carbonate and bicarbonate, in addition to modifying the solution pH, are also able to induce a considerable formation of the carbonate radicals upon nitrate photolysis. The higher availability of less-reactive species than the hydroxyl radical would contribute to substantially enhance the photodegradation of the phenols/phenolates that are sufficiently reactive toward the carbonate radical. This phenomenon has a potentially important impact on the fate of the relevant compounds in surface waters. In contrast, the degradation of compounds that are not sufficiently reactive toward CO(3)(-*) is inhibited by carbonate and bicarbonate because of the scavenging of *OH.