Iodine monoxide at a clean marine coastal site: observations of high frequency variations and inhomogeneous distributions

Commane, R.; Seitz, K.; Bale, Catherine S.E.; Bloss, William J.; Buxmann, Joelle; Ingham, T.; Platt, U.; Pöhler, Denis; Heard, Dwayne E.

doi:10.5194/acp-11-6721-2011

Cited by 29 publications

(32 citation statements)

References 49 publications

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“…Both studies are providing strong evidence that, in contrast to coastal regions where iodocarbon emissions of macroalgae are likely the major source for iodine (e.g. Seitz et al, 2010;Commane et al, 2011), in the open ocean direct marine emissions of inorganic iodine (here assumed to be I 2 ) are important as a source of reactive iodine in the MBL, in line with recent findings of Carpenter et al (2013). This conclusion is corroborated by the following findings of our study:…”

Section: Discussionsupporting

confidence: 92%

Iodine monoxide in the Western Pacific marine boundary layer

et al. 2013

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Abstract. A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved if an additional sea-air flux of inorganic iodine (e.g., I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.

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Section: Discussionsupporting

confidence: 92%

Iodine monoxide in the Western Pacific marine boundary layer

et al. 2013

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“…This is consistent with previous measurements of IO at Mace Head which showed maximum levels up to 5 pptv (Saiz-Lopez et al, 2006;Alicke et al, 1999). However, other measurements taken over "hot spots" of exposed seaweed beds have shown IO peak values of up to 50 pptv (Commane et al, 2011). Thus, it can be concluded that the observed background signal could be explained by the presence of IO that would nevertheless not contribute to atmospheric SO 2 oxidation because of a too small IO + SO 2 rate constant.…”

Section: Could X Be a Criegee Radical Produced From Ozonolysis?supporting

confidence: 80%

Missing SO<sub>2</sub> oxidant in the coastal atmosphere? – observations from high-resolution measurements of OH and atmospheric sulfur compounds

et al. 2014

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Abstract. Diurnal and seasonal variations of gaseous sulfuric acid (H 2 SO 4 ) and methane sulfonic acid (MSA) were measured in NE Atlantic air at the Mace Head atmospheric research station during the years 2010 and 2011. The measurements utilized selected-ion chemical ionization mass spectrometry (SI/CIMS) with a detection limit for both compounds of 4.3 × 10 4 cm −3 at 5 min signal integration. The H 2 SO 4 and MSA gas-phase concentrations were analyzed in conjunction with the condensational sink for both compounds derived from 3 nm to 10 µm (aerodynamic diameter) aerosol size distributions. Accommodation coefficients of 1.0 for H 2 SO 4 and 0.12 for MSA were assumed, leading to estimated atmospheric lifetimes on the order of 7 and 25 min, respectively. With the SI/CIMS instrument in OH measurement mode alternating between OH signal and background (non-OH) signal, evidence was obtained for the presence of one or more unknown oxidants of SO 2 in addition to OH. Depending on the nature of the oxidant(s), its ambient concentration may be enhanced in the CIMS inlet system by additional production. The apparent unknown SO 2 oxidant was additionally confirmed by direct measurements of SO 2 in conjunction with calculated H 2 SO 4 concentrations. The calculated H 2 SO 4 concentrations were consistently lower than the measured concentrations by a factor of 4.7 ± 2.4 when considering the oxidation of SO 2 by OH as the only source of H 2 SO 4 . Both the OH and the background signal were also observed to increase significantly during daytime aerosol nucleation events, independent of the ozone photolysis frequency, J (O 1 D), and were followed by peaks in both H 2 SO 4 and MSA concentrations. This suggests a strong relation between the unknown oxidant(s), OH chemistry, and the atmospheric photolysis and photooxidation of biogenic iodine compounds. As to the identity of the atmospheric SO 2 oxidant(s), we have been able to exclude ClO, BrO, IO, and OIO as possible candidates based on ab initio calculations. Nevertheless, IO could contribute significantly to the observed CIMS background signal. A detailed analysis of this CIMS background signal in context with recently published kinetic data currently suggests that Criegee intermediates (CIs) produced from ozonolysis of alkenes play no significant role for SO 2 oxidation in the marine atmosphere at Mace Head. On the other hand, SO 2 oxidation by small CIs such as CH 2 OO produced photolytically or possibly in the photochemical degradation of methane is consistent with our observations. In addition, H 2 SO 4 formation from dimethyl sulfide oxidation via SO 3 as an intermediate instead of SO 2 also appears to be a viable explanation. Both pathways need to be further explored.

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“…Observations of BrO and IO radicals within the MBL have demonstrated widespread impacts on atmospheric composition and chemistry (Alicke et al, 1999;Sander et al, 2003;Leser et al, 2003;Saiz-Lopez and Plane, 2004;SaizLopez et al, 2004SaizLopez et al, , 2006Peters et al, 2005;Whalley et al, 2007;Mahajan et al, 2010a;Commane et al, 2011;Dix et al, 2013;Gomez Martin et al, 2013;Le Breton et al, 2017), including significant effects on HO x concentrations and on the HO 2 : OH ratio in coastal and marine locations (Bloss et al, 2005a(Bloss et al, , 2010Sommariva et al, 2006;Kanaya et al, 2007;Whalley et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

et al. 2018

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Abstract. The chemistry of the halogen species bromine and iodine has a range of impacts on tropospheric composition, and can affect oxidising capacity in a number of ways. However, recent studies disagree on the overall sign of the impacts of halogens on the oxidising capacity of the troposphere. We present simulations of OH and HO 2 radicals for comparison with observations made in the remote tropical ocean boundary layer during the Seasonal Oxidant Study at the Cape Verde Atmospheric Observatory in 2009. We use both a constrained box model, using detailed chemistry derived from the Master Chemical Mechanism (v3.2), and the three-dimensional global chemistry transport model GEOSChem. Both model approaches reproduce the diurnal trends in OH and HO 2 . Absolute observed concentrations are well reproduced by the box model but are overpredicted by the global model, potentially owing to incomplete consideration of oceanic sourced radical sinks. The two models, however, differ in the impacts of halogen chemistry. In the box model, halogen chemistry acts to increase OH concentrations (by 9.8 % at midday at the Cape Verde Atmospheric Observatory), while the global model exhibits a small increase in OH at the Cape Verde Atmospheric Observatory (by 0.6 % at midday) but overall shows a decrease in the global annual mass-weighted mean OH of 4.5 %. These differences reflect the variety of timescales through which the halogens impact the chemical system. On short timescales, photolysis of HOBr and HOI, produced by reactions of HO 2 with BrO and IO, respectively, increases the OH concentration. On longer timescales, halogen-catalysed ozone destruction cycles lead to lower primary production of OH radicals through ozone photolysis, and thus to lower OH concentrations. The global model includes more of the longer timescale responses than the constrained box model, and overall the global impact of the longer timescale response (reduced primary production due to lower O 3 concentrations) overwhelms the shorter timescale response (enhanced cycling from HO 2 to OH), and thus the global OH concentration decreases. The Earth system contains many such responses on a large range of timescales. This work highlights the care that needs to be taken to understand the full impact of any one process on the system as a whole.

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Iodine monoxide at a clean marine coastal site: observations of high frequency variations and inhomogeneous distributions

Cited by 29 publications

References 49 publications

Iodine monoxide in the Western Pacific marine boundary layer

Iodine monoxide in the Western Pacific marine boundary layer

Missing SO<sub>2</sub> oxidant in the coastal atmosphere? – observations from high-resolution measurements of OH and atmospheric sulfur compounds

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

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Iodine monoxide at a clean marine coastal site: observations of high frequency variations and inhomogeneous distributions

Cited by 29 publications

References 49 publications

Iodine monoxide in the Western Pacific marine boundary layer

Iodine monoxide in the Western Pacific marine boundary layer

Missing SO&lt;sub&gt;2&lt;/sub&gt; oxidant in the coastal atmosphere? – observations from high-resolution measurements of OH and atmospheric sulfur compounds

Impacts of bromine and iodine chemistry on tropospheric OH and HO&lt;sub&gt;2&lt;/sub&gt;: comparing observations with box and global model perspectives

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Resources

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Missing SO<sub>2</sub> oxidant in the coastal atmosphere? – observations from high-resolution measurements of OH and atmospheric sulfur compounds

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives