Spontaneous oxidation of I - in water microdroplets and its atmospheric implications.

Atomic and molecular iodine, I˙ and I 2 , 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 I 2 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 I 2 - and I 3 - in water microdroplets, presenting a previously unknown source of I˙ and I 2 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.