Gaseous and particulate iodine in the marine atmosphere

Abstract

Sixty gaseous iodine samples collected from a 20-meter tower on the windward shore of Oahu, Hawaii, during the summer of 1969 showed that the concentration of gaseous iodine ranged from 5 to 20 ng/m3. Particulate samples collected simultaneously with the gaseous samples showed that the atmospheric concentrations of gaseous iodine in marine air are 2–4 times the concentration of particulate iodine. Statistical calculations indicate that the particulate iodine concentration and gaseous iodine concentrations are directly related. Thermodynamic calculations indicate that, if only inorganic ionic equilibriums including the species I−, IO3−, I2(g), and I2(aq) are considered, sea salt particles in the marine atmosphere should act as an almost perfect sink for gaseous iodine. Similar thermodynamic calculations indicate that the sea surface should also be a sink for gaseous iodine if the iodide concentration at the sea surface is that which has been reported for bulk sea water. Although the mechanism of gaseous iodine injection into the atmosphere is still uncertain, it is possible that gaseous iodine is released to the atmosphere as iodine-rich organic material decomposes at the surface of the ocean and on sea salt particles. The fact that particulate iodine concentration is inversely proportional to particle size may be explained by the atmospheric residence time of particulate matter if the ionic equilibrium reactions involving gaseous iodine and particulate iodine proceed slowly in relation to these residence times.