Bromide and other ions in the snow, firn air, and atmospheric boundary layer at Summit during GSHOX

Dibb, Jack E.; Ziemba, L. D.; Luxford, J.; Beckman, P.

doi:10.5194/acp-10-9931-2010

Cited by 53 publications

(67 citation statements)

References 42 publications

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“…Our analysis is consistent with the results of Dibb et al (2010), who also concluded that bromide in the snow is photochemically activated and released into the boundary layer. The levels of BrO from this mechanism are modulated by the actinic flux and the diurnal evolution of the boundary layer.…”

Section: Discussionsupporting

confidence: 82%

“…Summit is located on top of the Greenland ice sheet at 3200 m altitude and, with a distance of at least 400 km from the nearest ocean, removed from large halogen sources. Small amounts of chloride and bromide are found in surface snow at Summit (see Dibb et al, 2010), but it is to date unclear if reactive gaseous halogens are present at sufficiently high levels to have an influence on atmospheric chemistry.…”

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confidence: 99%

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Longpath DOAS observations of surface BrO at Summit, Greenland

et al. 2011

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Abstract. Reactive halogens, and in particular bromine oxide (BrO), have frequently been observed in regions with large halide reservoirs, for example during bromine catalyzed coastal polar ozone depletion events. Much less is known about the presence and impact of reactive halogens in areas without obvious halide reservoirs, such as the polar ice sheets or continental snow.We report the first LP-DOAS measurements of BrO at Summit research station in the center of the Greenland ice sheet at an altitude of 3200 m. BrO mixing ratios in May 2007 and June 2008 were typically between 1-3 pmol mol −1 , with maxima of up to 5 pmol mol −1 . These measurements unequivocally show that halogen chemistry is occurring in the remote Arctic, far from known bromine reservoirs, such as the ocean. During periods when FLEXPART retroplumes show that airmasses resided on the Greenland ice sheet for 3 or more days, BrO exhibits a clear diurnal variation, with peak mixing ratios of up to 3 pmol mol −1 in the morning and at night. The diurnal cycle of BrO can be explained by a changing boundary layer height combined with photochemical formation of reactive bromine driven by solar radiation at the snow surface. The shallow stable boundary layer in the morning and night leads to an accumulation of BrO at the surface, leading to elevated BrO despite the expected smaller release from the snowpack during these times of low solar radiation. During the day when photolytic formation of reacCorrespondence to: J. Stutz (jochen@atmos.ucla.edu) tive bromine is expected to be highest, efficient mixing into a deeper neutral boundary layer leads to lower BrO mixing ratios than during mornings and nights.The extended period of contact with the Greenland snowpack combined with the diurnal profile of BrO, modulated by boundary layer height, suggests that photochemistry in the snow is a significant source of BrO measured at Summit during the 2008 experiment.

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Section: Discussionsupporting

confidence: 82%

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confidence: 99%

Longpath DOAS observations of surface BrO at Summit, Greenland

et al. 2011

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“…3. Overall the levels of BrO were lower and less diurnally consistent in 2008 compared to 2007, even when comparing the same June overlap period Liao et al, 2011;Dibb et al, 2010). Total mercury in surface snow was slightly less in 2008 than in 2007 during the overlap period, and GEM showed significantly less variation in 2008.…”

Section: Resultsmentioning

confidence: 95%

“…These stable conditions change to neutral or slightly unstable conditions resulting in enhanced mixing depths of ∼70-250 m during an ∼8 h "daytime" period centered around local solar noon (Helmig et al, 2002). Chemical species thought to be emitted from the snowpack, such as NO and often BrO, showed diurnal profiles with minima at solar noon due to a larger mixing volume (Thomas et al, 2011a;Dibb et al, 2010). While a portion of the RGM and FPM diurnal dips, during 7-13 June 2008 period (Fig.…”

Section: Results From Selected Periodsmentioning

confidence: 99%

Temperature and sunlight controls of mercury oxidation and deposition atop the Greenland ice sheet

Brooks¹,

Moore

Lew³

et al. 2011

Atmos. Chem. Phys.

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Abstract. We conducted the first ever mercury speciation measurements atop the Greenland ice sheet at Summit Station (Latitude 72.6 • N, Longitude 38.5 • W, Altitude 3200 m) in the Spring and Summer of 2007 and 2008. These measurements were part of the collaborative Greenland Summit Halogen-HO x experiment (GSHOX) campaigns investigating the importance of halogen chemistry in this remote environment. Significant levels of BrO (1-5 pptv) in the near surface air were often accompanied by diurnal dips in gaseous elemental mercury (GEM), and in-situ production of reactive gaseous mercury (RGM). While halogen (i.e. Br) chemistry is normally associated with marine boundary layers, at Summit, Greenland, far from any marine source, we have conclusively detected bromine and mercury chemistry in the near surface air. The likely fate of the formed mercurybromine radical (HgBr) is further oxidation to stable RGM (HgBr 2 , HgBrOH, HgBrCl. . . ), or thermal decomposition. These fates appear to be controlled by the availability of Br, OH, Cl, etc. to produce RGM (Hg(II)), versus the lifetime of HgBr by thermal dissociation. At Summit, the production of RGM appears to require a sun elevation angle of >5 degrees, and an air temperature of < −15 • C. Possibly the availability of Br, controlled by photolysis J(Br 2 ), requires a sun angle >5 degrees, while the formation of RGM from HgBr requires a temperature < −15 • C . A portion of the deposited RGM is readily photoreduced and re-emitted to the air as GEM. However, a very small fraction becomes buried at depth. Extrapolating core samples from Summit to the Correspondence to: S. Brooks (steve.brooks@noaa.gov) entire Greenland ice sheet, we calculate an estimated net annual sequestration of ∼13 metric tons Hg per year, buried long-term under the sunlit photoreduction zone.

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“…Brooks et al (2011) concluded to the existence of bromine and mercury chemistry. It was suggested that snowpack photochemistry could be a possible source of BrO to the atmosphere (Dibb et al, 2010;Stutz et al, 2011). However the sources of bromide remained unclear and could be the falling snow and the transport of some bromine species from the free troposphere or marine regions.…”

Section: Examining Oxidation Pathways With Halogensmentioning

confidence: 99%

Dynamic recycling of gaseous elemental mercury in the boundary layer of the Antarctic Plateau

et al. 2012

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Abstract. Gaseous elemental mercury (Hg 0 ) was investigated in the troposphere and in the interstitial air extracted from the snow at Dome Concordia station (alt. 3320 m) on the Antarctic Plateau during January 2009. Measurements and modeling studies showed evidence of a very dynamic and daily cycling of Hg 0 inside the mixing layer with a range of values from 0.2 ng m −3 up to 2.3 ng m −3 . During low solar irradiation periods, fast Hg 0 oxidation processes in a confined layer were suspected. Unexpectedly high Hg 0 concentrations for such a remote place were measured under higher solar irradiation due to snow photochemistry. We suggest that a daily cycling of reemission/oxidation occurs during summer within the mixing layer at Dome Concordia.Hg 0 concentrations showed a negative correlation with ozone mixing ratios, which contrasts with atmospheric mercury depletion events observed during the Arctic spring. Unlike previous Antarctic studies, we think that atmospheric Hg 0 removal may not be the result of advection processes. The daily and dramatic Hg 0 losses could be a consequence of surface or snow induced oxidation pathways. It remains however unclear whether halogens are involved. The cycling of other oxidants should be investigated together with Hg species in order to clarify the complex reactivity on the Antarctic plateau.

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Bromide and other ions in the snow, firn air, and atmospheric boundary layer at Summit during GSHOX

Cited by 53 publications

References 42 publications

Longpath DOAS observations of surface BrO at Summit, Greenland

Longpath DOAS observations of surface BrO at Summit, Greenland

Temperature and sunlight controls of mercury oxidation and deposition atop the Greenland ice sheet

Dynamic recycling of gaseous elemental mercury in the boundary layer of the Antarctic Plateau

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