Imidazole-2-carboxaldehyde (IC) reactivity in the presence of halide anions (Cl^–, Br^–, I^–) has been studied by laser flash photolysis in aqueous solution at room temperature. The absorption spectrum of the triplet state of IC has been measured with a maximum absorption at 330nm and a weaker absorption band around 650nm. Iodide anions proved to be efficient quenchers of the triplet state IC, with a rate coefficient k_q of (5.33±0.25)×10⁹M⁻¹s⁻¹. Quenching by bromide and chloride anions was less efficient, with k_q values of (6.27±0.53)×10⁶M⁻¹s⁻¹ and (1.31±0.16)×10⁵M⁻¹s⁻¹, respectively. The halide (X^–) quenches the triplet state; the resulting transient absorption feature matches that of the corresponding radical anion (X₂^–). We suggest that this type of quenching reactions is a driving force of oxidation reactions in the oceanic surface microlayer (SML) and a source of halogen atoms in the atmosphere.