Inorganic iodine speciation in tropical Atlantic aerosol

Baker, Alex R.

doi:10.1029/2004gl020144

Cited by 90 publications

(108 citation statements)

References 15 publications

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“…The BASE case predicted comparatively low levels of HCHO (300−400 ppt in the OCEAN, AMERICA, and LOCAL scenarios and 400−500 ppt in the EUROPE scenario) and CH 3 In the presence of higher levels of aldehydes, Cl 2 mixing ratios were still within or closer to the range of the observations (in the OCEAN and EUROPE scenario, respectively), HOCl was underestimated by 5−30 ppt and BrCl was >10−20 ppt ( Figure S8). Because of the high reactivity with Br, aldehydes were very efficient in reducing the tendency of the model to overestimate bromine; however, Br inorg was still outside the range of the observations.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Sommariva

Glasow

2012

Environ. Sci. Technol.

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We used a one-dimensional model to simulate the chemical evolution of air masses in the tropical Atlantic Ocean, with a focus on halogen chemistry. The model results were compared to the observations of inorganic halogen species made in this region. The model could largely reproduce the measurements of most chlorine species, especially under unpolluted conditions, but overestimated sea salt chloride, BrCl, and bromine species. Agreement with the measurements could be improved by taking into account the reactivity with aldehydes and the effects of dimethyl sulfide (DMS) and Saharan dust on aerosol pH; a hypothetical HOX → X − aqueous-phase reaction could also improve the agreement with measured Cl 2 and HOCl, especially under semipolluted conditions. The results also showed that halogens speciation and concentrations are very sensitive to cloud processing. The model was used to calculate the impact of the observed levels of halogens: Cl atoms accounted for 5.4−11.6% of total methane sinks and halogens (mostly bromine and iodine) accounted for 35−40% of total ozone destruction. ■ INTRODUCTIONThe tropical marine boundary layer (MBL) is a region of particular interest for atmospheric chemistry: high levels of solar radiation, along with high temperatures and relative humidities, result in a highly oxidizing environment. It is estimated that the tropical atmosphere accounts for up to 80% of the global oxidation of methane (the second most important greenhouse gas) and that ∼25% of the global oxidation of methane occurs in the tropical MBL. 1 Halogen species (chlorine, bromine, iodine) are known to play an important role in the chemical processes of the MBL, particularly with regard to the nitrogen and ozone cycles, sulfur chemistry and particle formation: an overview of halogen chemistry and its impact on atmospheric chemical processes can be found in ref 2. Measurements of these species in the tropical region are sparse, but a number of recent studies 3−13 have reported observations of several halogen species in the tropical Atlantic Ocean. These studies suggested that halogen chemistry is responsible for a large fraction (∼30%) of ozone destruction in the Tropics 6 and up to 7% of the global methane destruction. 9 In this paper, we used the one-dimensional chemical model MISTRA to study halogen chemistry in the tropical Atlantic Ocean and the evolution of the chemical composition of air masses traveling across the ocean to the islands of Cape Verde, 900 km West of the coast of Africa. We compared the model results to the database of published observations of halogen species from this region with the objective of testing our understanding of halogen chemistry and of quantifying the impact of the observed halogens levels on ozone (O 3 ) and methane (CH 4 ). ■ METHODSModel. MISTRA is a one-dimensional model of the MBL. The model includes a description of meteorological and microphysical processes in the MBL and is described in detail in refs 14 and 15. Version 7.4.1 of MISTRA includes a number of improvement...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Sommariva

Glasow

2012

Environ. Sci. Technol.

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“…However, as already mentioned in the introduction, the scheme predicts negligible concentrations of I − but accumulation of IO − 3 in particles, both of which is not supported by an increasing number of observations (Baker, 2004(Baker, , 2005, as the most recent ones). Motivated by these obvious discrepancies, we found (after a thorough review of literature) that iodate might be reduced by pH-dependent reactions that are part of the complex system of the Dushman reaction (Dushman, 1904).…”

Section: Model Descriptionmentioning

confidence: 96%

“…Gas phase IO and OIO mixing ratios are both about 0.1 pmol mol −1 during daytime and approximately zero during nighttime. Please note that the concentrations of reactive iodine species in our model are far below the values measured in coastal regions (Alicke et al, 1999;Allan et al, 2001;Saiz-Lopez and Plane, 2004;Peters et al, 2005;Saiz-Lopez et al, 2006b), as we are trying to reproduce clean open ocean conditions. We assume a typical marine background aerosol size distribution (Hoppel and Frick, 1990) and distinguish between "sulfate" aerosol (dry aerosol radius <0.5 µm; initial composition 99.6% (NH 4 ) 2 SO 4 , 0.4% NH 4 NO 3 ) and "seasalt" aerosol (dry radius >0.5 µm; initial composition like sea water, initial pH like surface ocean water).…”

Section: Model Descriptionmentioning

confidence: 99%

“…In contrast, several observational data provide evidence for a non-negligible iodide content in aerosol samples (Gäbler and Heumann, 1993;Wimschneider and Heumann, 1995;Baker, 2004Baker, , 2005. Baker (2004Baker ( , 2005 determined the speciation of soluble iodine (iodide, iodate, organic iodine) during two extended ship cruises in the Atlantic Ocean and found highly variable I − /IO − 3 ratios. His measurements clearly show that the concentrations of iodide and iodate in aerosol are often of similar magnitude, that there are samples that do not contain iodate (but iodide), and that iodate is predominantly present in large aerosol (>1 µm diameter).…”

Section: Introductionmentioning

confidence: 99%

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Modelling iodide – iodate speciation in atmospheric aerosol: Contributions of inorganic and organic iodine chemistry

2007

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Abstract. The speciation of iodine in atmospheric aerosol is currently poorly understood. Models predict negligible iodide concentrations but accumulation of iodate in aerosol, both of which is not confirmed by recent measurements. We present an updated aqueous phase iodine chemistry scheme for use in atmospheric chemistry models and discuss sensitivity studies with the marine boundary layer model MIS-TRA. These studies show that iodate can be reduced in acidic aerosol by inorganic reactions, i.e., iodate does not necessarily accumulate in particles. Furthermore, the transformation of particulate iodide to volatile iodine species likely has been overestimated in previous model studies due to negligence of collision-induced upper limits for the reaction rates. However, inorganic reaction cycles still do not seem to be sufficient to reproduce the observed range of iodide -iodate speciation in atmospheric aerosol. Therefore, we also investigate the effects of the recently suggested reaction of HOI with dissolved organic matter to produce iodide. If this reaction is fast enough to compete with the inorganic mechanism, it would not only directly lead to enhanced iodide concentrations but, indirectly via speed-up of the inorganic iodate reduction cycles, also to a decrease in iodate concentrations. Hence, according to our model studies, organic iodine chemistry, combined with inorganic reaction cycles, is able to reproduce observations. The presented chemistry cycles are highly dependent on pH and thus offer an explanation for the large observed variability of the iodide -iodate speciation in atmospheric aerosol.

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“…Disagreement exists between observations of the atmospheric ratio of I − /IO 3 − , with one study of tropical Atlantic Ocean air finding a majority of IO 3 − and negligible I − [13] and another study finding non-negligible I − concentrations in aerosols [14]. Current models of atmospheric chemistry [3] find that the aerosol I − concentration is negligible due to its transformation into species that revert to the gas phase.…”

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confidence: 99%

Speciation analysis of iodine and bromine at picogram-per-gram levels in polar ice

Spolaor

Vallelonga²,

Gabrieli

et al. 2012

Anal Bioanal Chem

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Iodine and bromine species participate in key atmospheric reactions including the formation of cloud condensation nuclei and ozone depletion. We present a novel method coupling a high-performance liquid chromatography with ion chromatography and inductively coupled plasma mass spectrometry, which allows the determination of iodine (I) and bromine (Br) species (IO 3 − , I − , Br − , BrO 3 − ) at the picogram-per-gram levels presents in Antarctic ice. Chromatographic separation was achieved using an ION-PAC® AS16 Analytical Column with NaOH as eluent. Detection limits for I and Br species were 5 to 9 pg g −1 with an uncertainty of less than 2.5% for all considered species. Inorganic iodine and bromine species have been determined in Antarctic ice core samples, with concentrations close to the detection limits for iodine species, and approximately 150 pg g −1 for Br − . Although iodate (IO 3 − ) is the most abundant iodine species in the atmosphere, only the much rarer iodide (I − ) species was present in Antarctic Holocene ice. Bromine was found to be present in Antarctic ice as Br − .

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Inorganic iodine speciation in tropical Atlantic aerosol

Cited by 90 publications

References 15 publications

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Modelling iodide – iodate speciation in atmospheric aerosol: Contributions of inorganic and organic iodine chemistry

Speciation analysis of iodine and bromine at picogram-per-gram levels in polar ice

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