Effect of dissolved organic compounds on the photodegradation of the herbicide MCPA in aqueous solution.

This work shows that the addition of phenol and 2-propanol as model organic compounds significantly decreases the direct photolysis quantum yield of 4-chloro-2-methylphenoxyacetic acid (MCPA) upon UVB irradiation in aqueous solution. Laser flash photolysis data suggest that 2-propanol is able to decrease the formation of the MCPA excited states under irradiation. A decrease from 0.

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.

Bicarbonate-enhanced transformation of phenol upon irradiation of hematite, nitrate, and nitrite.

Bicarbonate enhances the transformation of phenol upon irradiation of hematite, and phenol nitration upon irradiation of both nitrate and nitrite. Hematite under irradiation is able to oxidise the carbonate ion to the CO3-. radical, which in turn oxidises phenol to the phenoxyl radical faster compared to the direct photo-oxidation of phenol by hematite.

Formation of organobrominated compounds in the presence of bromide under simulated atmospheric aerosol conditions.

Photobromination of phenol takes place upon UV/Vis irradiation of FeIII and bromide under acidic conditions, and most likely involves the brominating agent Br2(-*). Bromination is also observed in the presence of nitrate and bromide under UV irradiation, most likely involving Br2(-*) formed upon oxidation of bromide by *OH. Moreover, quantitative bromination of phenol is observed in the dark in the presence of hydrogen peroxide and bromide.