Emerging investigator series: spatial distribution of dissolved organic matter in ice and at air–ice interfaces

Chakraborty, Subha; Kahan, Tara F.

doi:10.1039/c9em00190e

Cited by 7 publications

(24 citation statements)

References 56 publications

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“…These three features were separated using a method described in the Supporting Information (section S1) and similar to our previous work. 28 Maps of samples containing 0.6 M NaCl and no HA were reanalyzed from our previous publication 11 using this method. The spectral decomposition method allowed us to evaluate two parameters at each coordinate:…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

“…25−27 We recently used Raman microscopy to show that citric acid is distributed throughout ice samples in liquid channels, similar to organic dyes, and that sodium dodecyl sulfate and HA were largely excluded to the ice surface, forming near-complete surface films as predicted for larger organic solutes by molecular dynamic simulations. 28 These theoretical and experimental results suggest that the environment presented to atmospheric species in the overlying atmosphere could vary depending on the physical properties of the major organic solute(s) (e.g., a uniform organic film, primarily bare ice with scattered clumps of OM or bare ice with liquid channels containing dissolved organic species). Uptake and reactivity could be very different for each type of surface described.…”

Section: ■ Introductionmentioning

confidence: 93%

“…27 In this work, we investigate the distributions of liquid water and solutes in laboratory-prepared proxies for sea ice containing various amounts of OM. Whereas we have previously investigated distributions of liquid water and hydrohalite in frozen aqueous NaCl solutions 11 and of liquid water and OM in frozen aqueous solutions containing OM, 28 it is not known what the liquid water and solute distributions in ternary water−NaCl−OM solutions will be. It is possible that reaction environments at OM-containing sea ice surfaces are distinct from those at freshwater ice surfaces in the presence and absence of OM and at sea ice surfaces in the absence of OM.…”

Section: ■ Introductionmentioning

confidence: 99%

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Physical Characterization of Frozen Aqueous Solutions Containing Sodium Chloride and Humic Acid at Environmentally Relevant Temperatures

Chakraborty

Kahan

2020

ACS Earth Space Chem.

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Sea ice presents a complex reaction medium containing poorly understood distributions of solutes, ice, and sometimes liquid brine. We studied the three-dimensional distribution of liquid brine and dissolved organic matter using confocal Raman microscopy at environmentally relevant sodium chloride (NaCl) and dissolved carbon concentrations in frozen ternary solutions containing NaCl and humic acid (HA). While HA is predominantly excluded to the ice surface in the absence of salt, it coexists with liquid brine in the micrometer scale channels throughout the entire ice sample when salt is present. HA increased the extent of liquid coverage of the ice surface at each temperature studied, but the total amount of liquid water at the surface did not increase. This suggests that HA promotes spreading of liquid water at the surface of frozen salt solutions, but does not increase the extent of surface melting. HA suppressed the phase transition from solid ice + liquid brine to solid ice + solid hydrohalite (NaCl•2H 2 O) when samples were cooled. Phase-transition temperatures ranged from (−26.4 ± 0.6) °C (with 0.003 mg/L HA) to (−33.7 ± 0.5) °C (with 30 mg/L HA), compared to (−22.3 ± 0.5) °C in the absence of HA. The phase transition in the reverse direction (as the samples were warmed) occurred at (−21.8 ± 0.5) °C, very close to the Eutectic temperature (−21.1 °C) at all HA concentrations and in the absence of HA.

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Section: ■ Materials and Methodsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 93%

Section: ■ Introductionmentioning

confidence: 99%

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Physical Characterization of Frozen Aqueous Solutions Containing Sodium Chloride and Humic Acid at Environmentally Relevant Temperatures

Chakraborty

Kahan

2020

ACS Earth Space Chem.

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“…We have shown that humic acid forms films that nearly completely cover ice surfaces at concentrations relevant to polar snow and ice. 23 At the surface of frozen seawater, we predict that anthracene will reside primarily in liquid brine channels, and that its reaction mechanism and kinetics will be determined both by self-association (possibly indicating bimolecular reactions) and by singlet oxygen formation.…”

Section: Discussionmentioning

confidence: 96%

“…18,19 The key to predicting reactivity of aromatic species (and perhaps non-aromatic species) in snow and ice may lie in elucidating the interactions of these species with each other and with their surroundings. Heterogeneous distribution of some inorganic [20][21][22] and organic solutes 23,24 at the air-ice interface has been demonstrated using microscopic techniques, but experimental observation of the distribution and speciation of aromatic pollutants at air-ice interfaces is not available. In this work we use wavelength-resolved fluorescence microscopy to investigate the distribution and chemical speciation of the aromatic pollutant anthracene adsorbed to frozen surfaces of atmospheric relevance and use these insights to explain anthracene photodegradation kinetics at frozen surfaces.…”

Section: Introductionmentioning

confidence: 99%

Direct Observation of Anthracene Clusters at Ice Surfaces

2022

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Heterogeneous processes can control atmospheric composition. Snow and ice present important, but poorly understood, reaction media that can greatly alter the composition of air in the cryosphere in polar and temperate regions. Atmospheric scientists struggle to reconcile model predictions with field observations in snow-covered regions due to experimental challenges associated with monitoring reactions at air-ice interfaces, and debate regarding reaction kinetics and mechanisms has persisted for over a decade. In this work, we use wavelength-resolved fluorescence microscopy to determine the distribution and chemical speciation of the pollutant anthracene at the surfaces of environmentally relevant frozen surfaces. We show that anthracene adsorbs to frozen surfaces in monomeric form, but that following lateral diffusion, molecules ultimately reside within brine channels at saltwater ice surfaces, and in micron-sized clusters at freshwater ice surfaces; emission profiles indicate extensive self-association. We also measure anthracene photodegradation kinetics in aqueous solution and artificial snow prepared from frozen freshwater and saltwater solutions and use the micro-spectroscopic observations to explain the rate constants measured in different environments. These results resolve long-standing debates and will improve predictions of pollutant fate in the cryosphere. The techniques used can be applied to numerous surfaces within and beyond the atmospheric sciences.

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Chemical Morphology Controls Reactivity of OH Radicals at the Air–Ice Interface

et al. 2021

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At the air−ice interface, some aromatic compounds such as benzene and anthracene are surprisingly unreactive toward OH. This may be a consequence of the poor solvation of these compounds at the interface, resulting in clustering there. We test this hypothesis by comparing the reaction of OH with pyrene, a 4ring polyaromatic hydrocarbon (PAH), to reactions of OH with the more water-soluble compounds coumarin and 7-hydroxycoumarin (7OHC). We observe that OH reacts readily with coumarin and 7OHC at both liquid and frozen air−water interfaces. Pyrene, a much less soluble compound, reacts with OH at the liquid surface but not at the air−ice interface. We report evidence of pyrene aggregation at the ice surface based on its broadened and redshifted emission spectrum alongside fluorescence mapping of anthracene, a closely related 3-ring PAH, which shows bunching at the ice surface. By contrast, fluorescence mapping shows that coumarin is fairly homogeneously distributed at the air−ice interface. Together, these results suggest that the limited reactivity of some compounds toward OH at the ice surface may be a consequence of their propensity to self-aggregate, demonstrating that chemical morphology can play an important role in reactions at the ice surface.

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Emerging investigator series: spatial distribution of dissolved organic matter in ice and at air–ice interfaces

Abstract: Organic solutes in snow and ice can be distributed heterogeneously throughout the ice bulk and across the ice surface. This may affect air-surface interactions and heterogeneous reactions in snow-covered regions.

Cited by 7 publications

References 56 publications

Physical Characterization of Frozen Aqueous Solutions Containing Sodium Chloride and Humic Acid at Environmentally Relevant Temperatures

Physical Characterization of Frozen Aqueous Solutions Containing Sodium Chloride and Humic Acid at Environmentally Relevant Temperatures

Direct Observation of Anthracene Clusters at Ice Surfaces

Chemical Morphology Controls Reactivity of OH Radicals at the Air–Ice Interface

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