Active chlorine release from marine aerosols: Roles for reactive iodine and nitrogen species

Recent laboratory measurements of the uptake of gaseous hypoiodous acid (HOI) on NaCl, NaBr, and sea‐salt surfaces have been used to aid calculation of the expected liberation of chlorine atoms from sea‐salt aerosol resulting from marine boundary layer (MBL) iodine chemistry. An existing model has been extended to include reactive chlorine chemistry resulting from two activation mechanisms. Measurements of the iodine monoxide (IO) and nitrate (NO 3 ) radicals from three recent field experiments have been used to constrain numerical simulations, investigating the relative importance of the iodine‐and nitrogen‐mediated mechanisms. These calculations show that the reactive uptake of both HOI and N 2 O 5 in the MBL can liberate Cl atoms from sea‐salt aerosol at a significant rate. A characteristic pulse of Cl production leading to several thousand molecules per cubic centimeter after sunrise may prove to be a useful diagnostic for the iodine‐mediated mechanism. Steady daytime production is predicted, leading to steady state [Cl] of several hundred to a few thousand molecules per cubic centimeter, perhaps over wide areas of the oceans. In addition, under certain conditions reactive bromine chemistry due to IBr release from fresh sea salt by reaction of HOI may dominate ICl production.