Spontaneous oxidation of I− in water microdroplets and its atmospheric implications

Atomic and molecular iodine, I˙ and I₂, play important roles in the atmosphere, such as the catalytic depletion of ozone and the oxidation of gaseous elemental mercury. It is known that the major source of I˙ and I₂ in the atmosphere is the photodissociation of organoiodine molecules released by algae in the sea. In this study, we show the striking results of the spontaneous and ultrafast oxidation of I^- into I˙, which further evolves into I₂^- and I₃^- in water microdroplets, presenting a previously unknown source of I˙ and I₂ in atmospheric water, such as the sea spray or cloud microdroplets. Mass spectrometric evidence shows that spontaneously generated hydroxyl radicals in water microdroplets are responsible for the oxidation of I^-. Taken together, we opine that microdroplet chemistry may adopt significant roles in atmospheric redox chemistry.