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Speciation of <sup>127</sup>I and <sup>129</sup>I in atmospheric aerosols at Risø, Denmark: insight into sources of iodine isotopes and their species transformations
oleh: L. Zhang, L. Zhang, X. Hou, X. Hou, S. Xu
Format: | Article |
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Diterbitkan: | Copernicus Publications 2016-02-01 |
Deskripsi
Speciation analysis of iodine in aerosols is a very useful approach for understanding geochemical cycling of iodine in the atmosphere. In this study, overall iodine species, including water-soluble iodine species (iodide, iodate and water-soluble organic iodine), NaOH-soluble iodine, and insoluble iodine have been determined for <sup>129</sup>I and <sup>127</sup>I in the aerosols collected at Risø, Denmark, during March and May 2011 (shortly after the Fukushima nuclear accident) and in December 2014. The measured concentrations of total iodine are in the range of 1.04–2.48 ng m<sup>−3</sup> for <sup>127</sup>I and (11.3–97.0) × 10<sup>5</sup> atoms m<sup>−3</sup> for <sup>129</sup>I, corresponding to <sup>129</sup>I ∕ <sup>127</sup>I atomic ratios of (17.8–86.8) × 10<sup>−8</sup>. The contribution of Fukushima-derived <sup>129</sup>I (peak value of 6.3 × 10<sup>4</sup> atoms m<sup>−3</sup>) is estimated to be negligible (less than 6 %) compared to the total <sup>129</sup>I concentration in northern Europe. The concentrations and species of <sup>129</sup>I and <sup>127</sup>I in the aerosols are found to be strongly related to their sources and atmospheric pathways. Aerosols that were transported over the contaminated seas contained higher concentrations of <sup>129</sup>I than aerosols transported over the European continent. The high <sup>129</sup>I concentrations of the marine aerosols are attributed to secondary emission of marine discharged <sup>129</sup>I in the contaminated seawater in the North Sea, North Atlantic Ocean, English Channel, Kattegat, etc., rather than direct gaseous release from the European nuclear reprocessing plants (NRPs). Water-soluble iodine was found to be a minor fraction to the total iodine for both <sup>127</sup>I (7.8–13.7 %) and <sup>129</sup>I (6.5–14.1 %) in ocean-derived aerosols, but accounted for 20.2–30.3 % for <sup>127</sup>I and 25.6–29.5 % for <sup>129</sup>I in land-derived aerosols. Iodide was the predominant form of water-soluble iodine, accounting for more than 97 % of the water-soluble iodine. NaOH-soluble iodine seems to be independent of the sources of aerosols. The significant proportion of <sup>129</sup>I and <sup>127</sup>I found in NaOH-soluble fractions is likely bound with organic substances. In contrast to water-soluble iodine, the sources of air masses exerted distinct influences on insoluble iodine for both <sup>129</sup>I and <sup>127</sup>I, with higher values for marine air masses and lower values for terrestrial air masses.