Release of nitric oxide and iodine to the atmosphere from the freezing of sea-salt aerosol components

The known room-temperature, solution-phase reaction between nitrite ions and iodide ions, which occurs in acidic conditions (pH < 5.5), is shown to be accelerated when neutral aqueous solutions are frozen. The reaction is proposed to occur in liquid "micropockets" within the ice structure at temperatures between the freezing point and the eutectic temperature. The products, nitric oxide and molecular iodine, are known to play significant roles in atmospheric compositional change, and therefore, the results obtained here, which are not dependent on acidification, may impact on observed snowpack chemistry. Investigation of the effect of oxygen on the chemical processing indicates that a chain reaction mechanism is operative.