Seaweed, Iodine, New Particles and Atmospheric Chemistry—The Current State of Play

The first events of coastal new particle formation have already been observed by Aitken in the late 19th century. Only a few years ago, however, a large field campaign at Mace Head, Ireland was dedicated to the investigation of bursts of new tiny atmospheric particles occurring at low tide. During the same campaign, iodine oxide was detected for the first time in the troposphere. A link between these two properties was rapidly established and since then an increasing number of studies tried to elucidate the exact processes behind this. This research involves scientists from very different fields, such as physics, chemistry, meteorology, climatology and biology, and researchers working in the field, laboratory and with numerical models, and has shown the potential relevance of inorganic iodine in the atmosphere for ozone and climate forcing. This Research Front collects a variety of papers that aim to answer questions about the processes and relevance of iodine for the atmosphere in general and foremost for coastal particle formation. In addition to Mace Head, iodine oxides have also been detected at the Cape Verde Islands, at Cape Grim (Tasmania, Australia), Kerguelen Islands, Antarctica, Brittany and on the Isles of Shoale off the coast of New England. Even more so than chlorine and bromine, iodine can very effectively destroy ozone, one of the most important substances in atmospheric chemistry. Unlike ozone destruction in the stratosphere, which is caused by anthropogenic halogens, the coastal events are entirely natural. Apart from the effect of iodine on photochemistry, the studies at Mace Head and in several laboratories have shown that very strong bursts of new aerosol particles with diameters of a few nanometers are produced by high concentrations of iodine oxides.