Atmospheric Chemistry of Iodine Alfonso Saiz-Lopez,* John M. C. Plane,* Alex R. Baker, Lucy J. Carpenter, Roland von Glasow, Juan C. G omez Martín, Gordon McFiggans, and Russell W. Saunders Laboratory for Atmospheric and Climate Science (CIAC), CSIC, Toledo, Spain School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom School of Earth, Atmospheric & Environmental Sciences, University of Manchester, Manchester, M13 9PL, United Kingdom

Atmospheric Chemistry of Iodine

In the past 40 years, atmospheric chemists have come to realize that halogens exert a powerful influence on the chemical composition of the troposphere and through that influence affect the fate of pollutants and may affect climate. Of particular note for climate is that halogen cycles affect methane, ozone, and particles, all of which are powerful climate forcing agents through direct and indirect radiative effects. This influencecomes from the high reactivity of atomic halogen radicals (e.g.,Cl, Br, I) and halogen oxides (e.g., ClO, BrO, IO, and higher oxides), known as reactive halogen species in this review. These reactive halogens are potent oxidizers for organic and inorganic compounds throughout the troposphere.

Tropospheric Halogen Chemistry: Sources, Cycling,and Impacts

https://orbit.dtu.dk/files/4023711/ACA-Review-129I-speciation-finalversion.pdf

A review on speciation of iodine-129 in the environmental and biological samples

Halogen chemistry is well known for ozone destruction in the stratosphere, however reactive halogens also play an important role in the chemistry of the troposphere. In the last two decades, an increasing number of reactive halogen species have been detected in a wide range of environmental conditions from the polar to the tropical troposphere. Growing observational evidence suggests a regional to global relevance of reactive halogens for the oxidising capacity of the troposphere. This critical review summarises our current understanding and uncertainties of the main halogen photochemistry processes, including the current knowledge of the atmospheric impact of halogen chemistry as well as open questions and future research needs.

Reactive halogen chemistry in the troposphere

. Temporal variations in the amount of radionuclides released into the atmosphere during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident and their atmospheric and marine dispersion are essential to evaluate the environmental impacts and resultant radiological doses to the public. In this paper, we estimate the detailed atmospheric releases during the accident using a reverse estimation method which calculates the release rates of radionuclides by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric and oceanic transport, dispersion and deposition models. The atmospheric and oceanic models used are WSPEEDI-II (Worldwide version of System for Prediction of Environmental Emergency Dose Information) and SEA-GEARN-FDM (Finite difference oceanic dispersion model), both developed by the authors. A sophisticated deposition scheme, which deals with dry and fog-water depositions, cloud condensation nuclei (CCN) activation, and subsequent wet scavenging due to mixed-phase cloud microphysics (in-cloud scavenging) for radioactive iodine gas (I2 and CH3I) and other particles (CsI, Cs, and Te), was incorporated into WSPEEDI-II to improve the surface deposition calculations. The results revealed that the major releases of radionuclides due to the FNPS1 accident occurred in the following periods during March 2011: the afternoon of 12 March due to the wet venting and hydrogen explosion at Unit 1, midnight of 14 March when the SRV (safety relief valve) was opened three times at Unit 2, the morning and night of 15 March, and the morning of 16 March. According to the simulation results, the highest radioactive contamination areas around FNPS1 were created from 15 to 16 March by complicated interactions among rainfall, plume movements, and the temporal variation of release rates. The simulation by WSPEEDI-II using the new source term reproduced the local and regional patterns of cumulative surface deposition of total 131I and 137Cs and air dose rate obtained by airborne surveys. The new source term was also tested using three atmospheric dispersion models (Modele Lagrangien de Dispersion de Particules d'ordre zero: MLDP0, Hybrid Single Particle Lagrangian Integrated Trajectory Model: HYSPLIT, and Met Office's Numerical Atmospheric-dispersion Modelling Environment: NAME) for regional and global calculations, and the calculated results showed good agreement with observed air concentration and surface deposition of 137Cs in eastern Japan.

/pdf/detailed-source-term-estimation-of-the-atmospheric-release-17h8zqzsdq.pdf

Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model

Iodine oxides, such as iodate, should be the only thermodynamically stable sink species for iodine in the tro- posphere. However, field observations have increasingly found very little iodate and significant amounts of iodide and soluble organically bound iodine (SOI) in precipitation and aerosols. The aim of this study was to investigate io- dine speciation, including the organic fraction, in rain, snow, and aerosols in an attempt to further clarify aqueous phase iodine chemistry. Diurnal aerosol samples were taken with a 5 stage cascade impactor and a virtual impactor (PM2.5) from the Mace Head research station, Ireland, during sum- mer 2006. Rain was collected from Australia, New Zealand, Patagonia, Germany, Ireland, and Switzerland and snow was obtained from Greenland, Germany, Switzerland, and New Zealand. Aerosols were extracted from the filters with water and all samples were analysed for total soluble iodine (TSI) by inductively coupled plasma mass spectrometry (ICP-MS) and iodine speciation was determined by coupling an ion chromatography unit to the ICP-MS. The median concentra- tion of TSI in aerosols from Mace Head was 222 pmol m 3 (summed over all impactor stages) of which the majority was associated with the SOI fraction (median day: 90±4%, night: 94±2% of total iodine). Iodide exhibited higher concen- trations than iodate (median 6% vs. 1.2% of total iodine), and displayed significant enrichment during the day com- pared to the night. Interestingly, up to 5 additional, presum- ably anionic iodo-organic peaks were observed in all IC-ICP- MS chromatograms, composing up to 15% of the TSI. Sol- uble organically bound iodine was also the dominant frac- tion in all rain and snow samples, with lesser amounts of iodide and iodate (iodate was particularly low in snow). Two of the same unidentified peaks found in aerosols were also observed in precipitation from both Southern and Northern Hemispheres. This suggests that these species are transferred from the aerosols into precipitation and that they have ei- ther a relatively long lifetime or are rapidly recycled. It is thought that SOI is formed by reactions between HOI or I2 and organic matter derived from the ocean surface layer. SOI may then photolytically decompose to yield iodide and the unidentified species. The data in this study show that io- dine oxides are the least abundant species in rain, snow, and aerosols and therefore considerably more effort is required on aqueous phase iodine chemistry for a holistic understand- ing of the iodine cycle.

/pdf/iodine-speciation-in-rain-snow-and-aerosols-2t51bwjoy3.pdf

Iodine speciation in rain, snow and aerosols

[1] Atmospheric iodine models currently predict iodate as the only stable iodine sink species in the troposphere. However, it is shown here using ion chromatograph inductively coupled plasma-mass spectroscopy (IC-ICP-MS) that iodate is the least abundant iodine species in precipitation (rain and snow) collected from various locations in southern Germany, the Swiss Alps, and Patagonia (Chile). The majority of iodine is associated with organic compounds (average 56%) followed by iodide (average 27%). Although the exact structure of the organic fraction remains ambiguous and is probably of higher molecular weight, a smaller portion of the iodo-organic compounds are anionic (5–20% of total I). One of these anionic organo-I peaks is present in all rain and most snow chromatograms and is generally responsible for 5–18% of total iodine. This suggests a ubiquitous atmospheric iodine species. The data indicate that organic iodine compounds play an important role in the global atmospheric iodine cycle and the atmospheric iodine sink. As such, future tropospheric iodine models must consider organic-I reactions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006JD007356

Iodine speciation in rain and snow: Implications for the atmospheric iodine sink

Iodine is an essential trace element for all mam- mals and may also influence climate through new aerosol formation. Atmospheric bromine cycling is also important due to its well-known ozone depletion capabilities. Despite precipitation being the ultimate source of iodine in the ter- restrial environment, the processes effecting its distribution, speciation and transport are relatively unknown. The aim of this study was to determine the effect of orographically induced precipitation on iodine concentrations in snow and also to quantify the inorganic and organic iodine and bromine species. Snow samples were collected over an altitude profile ( 840 m) from the northern Black Forest and were analysed by ion-chromatography - inductively coupled plasma mass spectrometry (IC-ICP-MS) for iodine and bromine species and trace metals (ICP-MS). All elements and species concen- trations in snow showed significant ( r 2 >0.65) exponential decrease relationships with altitude despite the short (5 km) horizontal distance of the transect. In fact, total iodine more than halved (38 to 13 nmol/l) over the 840 m height change. The results suggest that orographic lifting and subsequent precipitation has a major influence on iodine concentrations in snow. This orographically induced removal effect may be more important than lateral distance from the ocean in determining iodine concentrations in terrestrial precipitation. The microphysical removal process was common to all ele- ments indicating that the iodine and bromine are internally mixed within the snow crystals. We also show that organ- ically bound iodine is the dominant iodine species in snow (61-75%), followed by iodide. Iodate was only found in two samples despite a detection limit of 0.3 nmol/l. Two un- known but most likely anionic organo-I species were also identified in IC-ICP-MS chromatograms and comprised 2- 10% of the total iodine. The majority of the bromine was inorganic bromide with a max. of 32% organo-Br.

/pdf/iodine-and-bromine-speciation-in-snow-and-the-effect-of-3un369n7bq.pdf

Iodine and bromine speciation in snow and the effect of orographically induced precipitation

Iodine is a vital micronutrient for all mammals, including humans. Despite iodine's listing by the WHO as the world's most easily preventable cause of brain damage, there is very little known about iodine cycling in terrestrial freshwaters, particularly regarding temporal changes in speciation. This study presents iodine speciation (measured by IC-ICP-MS) data from one year of monthly sampling of a dimictic humic lake in the Black Forest (Mummelsee). Total soluble iodine (TSI) levels in the Mummelsee's water column averaged 1.9 ± 0.3 μg L-1. Soluble organically bound iodine (SOI) accounted for the majority of TSI in the lake (85 ± 7%) and inflow (76 ± 6%). SOI showed few changes throughout the year, despite stratification, anoxia in the hypolimnion and ice cover. Iodide was lost from the epilimnion during the summer, autumn and winter, which may be related to (micro)biological uptake and sedimentation of dead organic matter. Efficient biological uptake was also suggested by a sediment core, where we found high total iodine concentrations (av. 11.8 ± 1.7 mg kg-1) and a significant correlation with organic carbon content (p <0.001). In the hypolimnion a strong iodide flux was observed from the sediments into the water column during lake stratification and low DO levels. Based on I/Corg ratios in the sediment core, the iodide flux into the lake probably occurs by biological decomposition of organic material in the upper 20 cm of the sediments. Iodate levels in the epilimnion increased consistently over the year, whereas it was reduced below detection limits in the hypolimnion during anoxia. The winter turnover lead to reintroduction of oxygen into the hypolimnion and rapid formation of iodate and SOI. During the turnover event, near complete loss of iodide from the water column was also observed. SOI will play the largest role in iodine cycling in the Mummelsee; however, further studies are needed on the biological transformation of iodine species in freshwaters for a more complete understanding of iodine cycling.

/pdf/iodine-speciation-and-cycling-in-fresh-waters-a-case-study-3mf5k6ee43.pdf

Michael Petri

Papers

Iodine speciation in rain, snow and aerosols

Iodine speciation in rain and snow: Implications for the atmospheric iodine sink

Iodine and bromine speciation in snow and the effect of orographically induced precipitation

Iodine speciation and cycling in fresh waters: a case study from a humic rich headwater lake (Mummelsee)

An iodine mass-balance for Lake Constance, Germany: insights into iodine speciation changes and fluxes