On the Speciation of Iodine in Marine Aerosol

Abstract

Iodine has a profound impact on tropospheric chemistry through its role in ozone depletion, particle formation, and impact on the oxidative capacity (see Saiz-Lopez et al., 2012, and references therein). In a previous publication (Gómez Martín et al., 2021), we reported the spatial variability of total iodine (TI) in aerosol by compiling and homogenizing a comprehensive data set of field observations at open ocean, insular, and coastal locations and appending to it previously unpublished measurements, spanning a period of 55 years. The analysis of the latitudinal and longitudinal dependence of TI in aerosol provided for the first time observational evidence from the field showing that the dominant global source of atmospheric iodine to the atmosphere is the reaction between iodide and ozone on the sea-water interface (Carpenter et al., 2013). After uptake on particle surfaces, iodine undergoes a rich aqueous-phase chemistry, which is known to depend on the origin and chemical properties of the aerosol (e.g., acidity ) but still remains poorly understood. Iodine speciation determines whether recycling to the gas phase can proceed through formation of volatile species, which is thought to occur via iodide (I − ), or aerosol becomes essentially an atmospheric iodine sink through accumulation of species assumed to be stable and unreactive, that is, iodate (IO 3 − ; Vogt et al., 1999). However, current aerosol chemical schemes cannot explain the concentrations of I − , IO 3 − , and soluble organic iodine (SOI) observed in field campaigns. Models predict negligible concentrations of I − following recycling to the gas phase and high concentrations of IO 3 − ,

Environmental iodine speciation quantification in seawater and snow using ion exchange chromatography and UV spectrophotometric detection

“…The heights are given in centimetres (cm) from the snow sea-ice interface (0 cm). Errors for IO iodide in the late summer Arctic sea-ice snow samples were similar to those in rain, continental snow and aerosol [29,30,79,78] but significantly different to what occurs in marine surface waters (Section 3.2).…”

“…Nevertheless, Wong and Cheng [70] found that the presence of dissolved organic iodine is important in the oceans, and therefore likely in other environments, because it easily converts to iodide. In marine atmospheric aerosol, iodine speciation is poorly understood but dissolved organic iodine has been found to comprise the major component of the soluble iodine content of fine aerosol [30]. Conversion of dissolved organic iodine to iodide could be an important mechanism to recycle particle phase iodine to the gas phase, which is thought to occur via iodide [71].…”

“…The conserved concentration of total dissolved iodine in seawater can be breached through the lateral migration of low oxygen continental shelf/shelf slope/estuarine and coastal waters across the sediment interface, producing a flux of iodine from sediments into ocean basins resulting in higher than expected concentrations [27,28]. In other aqueous systems, the iodine species composition is more variable and concentrations of dissolved organic iodine can be equal to or greater than iodide in estuarine waters, groundwater, rainwater, snow and atmospheric aerosol [23,26,[29][30][31].…”

Chemical Implications of Rapid Reactive Absorption of I2O4 at the Air-Water Interface

“…Even in field-collected aerosols, I 2 O 4 was also absent, and the detected soluble iodine was primarily iodate anion (IO 3 − ), 17 whose concentration cannot be interpreted by current aerosol chemical schemes. 18 I 2 O 4 was speculated to be hydrolyzed to HIO 3 (I 2 O 4 + H 2 O → HIO 3 + HIO 2 ) and detected as IO 3 − in aqueous aerosol. 17,18 In the humid marine environment (RH = 70−80%), 19 this hypothesis, if valid, seems to explain well the link of the mysterious fate of I 2 O 4 , the missing source of IO 3 − , and aerosol growth.…”

“…24 Moreover, due to the uptake of gaseous iodine species, iodine is reported to be more enriched in aerosol than in seawater. 18,25 Considering all the evidence, it is necessary and essential to explore the air−water interfacial reaction of I 2 O 4 mediated by H 2 SO 4 and amines, which could be a potential driver for marine aerosol growth.…”