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

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