Photooxidation of Halides by Chlorophyll at the Air-Salt Water Interface

Glancing angle laser-induced fluorescence was used to follow the kinetics of chlorophyll loss at the air-salt water interface under the influence of visible radiation. Aqueous solutions of NaCl, NaBr, NaI, KNO3, and NaNO2 in a range of concentrations up to similar to 1 M were used as substrates. The first-order reaction rate depends linearly on salt concentration for the halide salts but does not vary with concentration for nitrate or nitrite salts. At the same salt concentration, the chlorophyll loss rate is greatest for the bromide-containing solutions, followed by those containing chloride and then iodide. The results are consistent with a mechanism in which photoproduced chlorophyll cations are reduced by halide anions and subsequently react with the halogen atoms thus produced. This mechanism gives a novel route for gas-phase halogenated species, and possibly nitrogen oxides, to be released to the marine boundary layer.