Iodine speciation in rain and snow: Implications for the atmospheric iodine sink

Atmospheric iodine models currently predict iodate as the only stable iodine sink species in the troposphere. However, it is shown here using ion chromatograph inductively coupled plasma-mass spectroscopy (IC-ICP-MS) that iodate is the least abundant iodine species in precipitation ( rain and snow) collected from various locations in southern Germany, the Swiss Alps, and Patagonia ( Chile). The majority of iodine is associated with organic compounds ( average 56 ) followed by iodide ( average 27 ). Although the exact structure of the organic fraction remains ambiguous and is probably of higher molecular weight, a smaller portion of the iodo-organic compounds are anionic (5-20 of total I). One of these anionic organo-I peaks is present in all rain and most snow chromatograms and is generally responsible for 5-18 of total iodine. This suggests a ubiquitous atmospheric iodine species. The data indicate that organic iodine compounds play an important role in the global atmospheric iodine cycle and the atmospheric iodine sink. As such, future tropospheric iodine models must consider organic-I reactions.