Sulphuric acid at grain boundaries in Antarctic ice

Mulvaney, Robert; Wolff, Eric W.; Oates, K.

doi:10.1038/331247a0

Cited by 196 publications

(175 citation statements)

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“…There is however good support for our assumed NO 3 À distribution in ice from observations of its tendency to accumulate at ice grain boundaries and from laboratory measurements. [24,34,35] Future work seeking to address the oxidising capacity due to OH within the snowpack through either measurements of its production and losses, or by direct observation would add support to this work too. The next uncertainty that we discuss again relates to scenario 3 in part two and it is the speciation and abundance of the OM detected in the snowpack.…”

Section: Resultsmentioning

confidence: 99%

“…[32] Concentrations of acidic solutes were found to be present at concentrations of ,10 mM at the South Pole. [33] However, because of the tendency of solutes to migrate to the surface layer in ice, [34,35] concentrations may become locally enhanced up to the 100-mM range [33] in the surface region.…”

Section: Ch 3 Ooh As a Source Of Hchomentioning

confidence: 99%

“…Furthermore, observations of the distribution of acid solutes within ice grains show a tendency for NO 3 À to accumulate at ice grain Chemical production of HCHO in the South Pole snowpack boundaries. [34,35] We also assume that OH produced in the bulk can only penetrate through four monolayers to reach the surface [40] due to the effects of Eqn 6a. Note that the results in Table 1 showing effective OM concentrations for particles of acetophenone of 0.035 mm in diameter are relevant in this scenario.…”

Section: Scenariomentioning

confidence: 99%

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Investigating the photo-oxidative and heterogeneous chemical production of HCHO in the snowpack at the South Pole, Antarctica

et al. 2014

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Environmental context. Snowpacks present a surprisingly active environment for photochemistry, leading to sunlight-induced oxidation of deposited organic matter and the subsequent emission of a variety of photochemically active trace gases. We seek to address questions regarding the ultimate fate of organic matter deposited onto snow in the remote regions of the world. The work is relevant to atmospheric composition and climate change.Abstract. We investigate snowpack fluxes of formaldehyde (HCHO) into the South Pole boundary layer using steadystate photochemical models. We study two chemical sources of HCHO within the snowpack. First, we study chemical production of HCHO from the processing of methyl hydroperoxide (CH 3 OOH): photolysis, reaction with the hydroxyl radical (OH ), and by an acid catalysed rearrangement. Assuming surface layer concentration effects for acidic solutes, we show that the acid catalysed production of HCHO within ice could contribute a non-negligible source to the snowpack HCHO budget. This novel source of HCHO complements existing explanations of HCHO fluxes based on physical emission of HCHO from snow. Secondly, we investigate HCHO production from the oxidation of organic matter (OM) by OH within snow to explain observed fluxes of photochemical origin from the South Pole snowpack. This work shows that laboratory-derived photochemical production rates of HCHO and our standard model are inconsistent with field observations, which has implications for the distribution of OM relative to oxidants within ice particles. We resolve this inconsistency using new laboratory measurements of the molecular dynamics of the OH photofragment from hydrogen peroxide (H 2 O 2 ) and nitrate (NO 3 À ) photolysis, which show that only OH produced in the outermost monolayers can contribute to gas phase and surface layer chemistry. Using these new measurements in conjunction with realistic treatments of ice grain size, H 2 O 2 and NO 3 À distribution within ice grains, diffusion of gas species within solid ice, and observed OM particle size distributions yields snowpack HCHO photochemical production rates more consistent with observations.

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Section: Resultsmentioning

confidence: 99%

Section: Ch 3 Ooh As a Source Of Hchomentioning

confidence: 99%

Section: Scenariomentioning

confidence: 99%

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Investigating the photo-oxidative and heterogeneous chemical production of HCHO in the snowpack at the South Pole, Antarctica

et al. 2014

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“…The combination of these two techniques not only enables them to characterize the structural features of a sample but also permits them to identify the elemental constituents and contaminants that may be present. These techniques have been used to analyze snowflakes (Wolff and Reid, 1994), but have been more extensively applied to identifying impurities and their distribution in natural ices Iliescu et al, 2002), including Vostok ice and polar ice (Barnes et al, 2001;Cullen and Baker, 2000;Mulvaney et al, 1988;Wolff et al, 1988). Future research in this area may provide valuable information on the type and source of pollutants that are captured during snow and ice formation, as well as on how the elemental composition of polar and glacial ice changes through the ages.…”

Section: Discussionmentioning

confidence: 99%

“…These problems were solved by equipping the SEM with a cold stage that maintained the temperature of the ice sample near that of liquid nitrogen. As a result, samples of ice could be imaged, analyzed, and photographed (Barnes et al, 2001;Baker, 2000, 2002;Dominé et al, 2001;Iliescu et al, 2002;Kuroiwa, 1969;Muguruma, 1961;Mulvaney et al, 1988;Wolff et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Collecting, shipping, storing, and imaging snow crystals and ice grains with low‐temperature scanning electron microscopy

Erbe

Rango

Foster

et al. 2003

Microscopy Res & Technique

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Methods to collect, transport, and store samples of snow and ice have been developed that enable detailed observations of these samples with a technique known as low-temperature scanning electron microscopy (LTSEM). This technique increases the resolution and ease with which samples of snow and ice can be observed, studied, and photographed. Samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far as 5,000 miles. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. The samples are not subjected to the melting or sublimation artifacts. LTSEM allows individual crystals to be observed for several hours with no detectable changes. Furthermore, the instrument permits recording of photographs containing the parallax information necessary for three-dimensional imaging of the true shapes of snowflakes, snow crystals, snow clusters, ice grains, and interspersed air spaces. This study presents detailed descriptions of the procedures that have been used successfully in the field and the laboratory to collect, ship, store, and image snow crystals and ice grains.

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Surface and Englacial Drainage of Glaciers and Ice Sheets

Nienow

Hubbard

2005

Encyclopedia of Hydrological Sciences

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Supraglacial drainage occurs wherever snowpack, firn, or ice at the glacier surface is at the pressure melting point and supplied with additional energy, thereby generating melt water. Energy sources vary, but net radiation is usually the dominant source, although inputs of rainwater can also provide large volumes of surface runoff. The surface melt water is routed through the snowpack, firn, and across the glacier surface according to the local hydraulic gradient. In general, routing of water through snow and firn is slow (10 −4 –10 −5 m s −1 ), contributing to a significant lag between melt water production and runoff at the glacier snout, whereas flow across exposed ice surfaces is typically 3–5 orders of magnitude faster. Under certain conditions where parts of the snowpack, firn, and/or ice surface are below the pressure melting point, the melt water will refreeze. Otherwise, the melt water will be routed supraglacially to the glacier margin unless intersected by a pathway from the glacier surface to the glacier interior. Such pathways include crevasses and moulins, and in temperate glaciers, microscale englacial veins. Flow rates through the englacial system vary considerably according to the hydraulic efficiency of the route taken. The routing of melt waters through both supraglacial and englacial drainage systems therefore affects the runoff response of an ice mass to rain and melt water inputs. During the course of a melt season, the efficiency of routing through both systems evolves, thereby altering the runoff response time to input variations.

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Sulphuric acid at grain boundaries in Antarctic ice

Cited by 196 publications

References 8 publications

Investigating the photo-oxidative and heterogeneous chemical production of HCHO in the snowpack at the South Pole, Antarctica

Investigating the photo-oxidative and heterogeneous chemical production of HCHO in the snowpack at the South Pole, Antarctica

Collecting, shipping, storing, and imaging snow crystals and ice grains with low‐temperature scanning electron microscopy

Surface and Englacial Drainage of Glaciers and Ice Sheets

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