Speciation of 127 I and 129 I in atmospheric aerosols at Risø, Denmark: insight into sources of iodine isotopes and their species transformations

• Published in: Atmospheric Chemistry and Physics
• Main Authors: L. Zhang, X. Hou, S. Xu
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2016
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Fukushima; Kattegat; North Atlantic
• Online Access: https://doi.org/10.5194/acp-16-1971-2016; https://doaj.org/article/960484a6cf3b4c56a3da2a43543c4987

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 129 I and 127 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 −3 for 127 I and (11.3–97.0) × 10 5 atoms m −3 for 129 I, corresponding to 129 I ∕ 127 I atomic ratios of (17.8–86.8) × 10 −8 . The contribution of Fukushima-derived 129 I (peak value of 6.3 × 10 4 atoms m −3 ) is estimated to be negligible (less than 6 %) compared to the total 129 I concentration in northern Europe. The concentrations and species of 129 I and 127 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 129 I than aerosols transported over the European continent. The high 129 I concentrations of the marine aerosols are attributed to secondary emission of marine discharged 129 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 127 I (7.8–13.7 %) and 129 I (6.5–14.1 %) in ocean-derived aerosols, but accounted for 20.2–30.3 % for 127 I and 25.6–29.5 % for 129 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 129 I and 127 I found in NaOH-soluble fractions is likely bound with organic substances. In ...