Iodine concentration and availability in atmospheric aerosol

Iodine has been determined in aerosol samples collected at a coastal site in southeast England using instrumental neutron activation analysis (INAA) and by an electrochemical technique, after aqueous extraction. Size distribution and enrichment factor data for the samples are consistent with a non-sea-salt source of iodine, presumably gas-to-particle conversion of volatile iodocarbons. On average, only ∼70% of INAA (i.e. total) iodine could be released from the aerosols as inorganic iodine by aqueous extraction at 95°C. Extraction at a more environmentally realistic temperature (20°C) decreased this yield to ∼25%. Through the use of high-energy UV light, which is known to destroy organic matter, the yield of aqueous extractable iodine at the lower temperature was increased for some samples. Thus, it appears likely that iodine is present in aerosol in varying proportions as soluble inorganic iodine, soluble organic iodine and insoluble, or unextractable, iodine. The different characteristics of these fractions are likely to have significant impacts on the cycling and reactivity of iodine in the atmosphere.