Iodine speciation in marine aerosol

• Main Author: Yodle, Chan
• Published: University of East Anglia 2015
• Subjects: 577
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.679150

Iodine chemistry in the marine aerosol plays important roles in the marine boundary layer such as ozone destruction and new aerosol particle formation. Iodine has a complex chemistry in the gas and aerosol phases and to date, what controls iodine speciation, the interactions and roles of individual iodine species are not well understood. This research aims to identify key controls on iodine speciation in marine aerosol. Effects of filter types on iodine and extraction methods were tested to provide optimum conditions for extraction of iodine species. Coupling of ion chromatography and inductively coupled plasma – mass spectrometry (IC-ICP-MS) for the measurement of iodine speciation was developed to provide a reliable analytical method. These optimised methods were used to determine iodine speciation in samples collected during cruises in the Atlantic Ocean (AMT21) and the Pacific Ocean (TransBrom and SHIVA). Major ions were also determined in these samples by ion chromatography (IC) with the results providing insight into the chemical characteristics aerosol samples. A high variability of the total soluble iodine (TSI) was observed between AMT21 (12–82, median 30 pmol m-3) and TransBrom (1.6–27, median 6.9 pmol m-3) and SHIVA (5.9–15, median 8.4 pmol m-3). The proportions of iodide (I-), iodate (IO3-) and soluble organic iodine (SOI) on the three cruises also showed a high variability: AMT21: I- 5.2–39%, median 14%; IO3- 36–99%, median 66%; and SOI 13–47%, median 28%, TransBrom: I- 8.8–64%, median 46%; IO3- 1.8–65%, median 6.2%; and SOI 5.9–50%, median 39%, SHIVA: I- 22–79%, median 42%; IO3- 17–66%, median 39%; and SOI non-determinable value–41%, median 14%. Three main types of aerosol with distinctive iodine speciation were identified: polluted aerosol, clean seasalt and mineral dust. pH seems to play an important role in regulating iodine speciation. The formation of HOI and the reduction of iodate are driven by acidic conditions in polluted aerosol. In clean less acidic seasalt aerosol, a high iodine enrichment was observed (565–1675, median 725), especially in the fine mode aerosol. For mineral dust, uptake of HIO3 on calcium carbonate surfaces seems to dominate.