Physical Chemistry of the Air-Water Interface

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Biosphere/Hydrosphere/Land–Atmosphere Interactions".

Deadline for manuscript submissions: closed (15 October 2018) | Viewed by 20859

Special Issue Editor


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Guest Editor
Linde Laboratories, California Institute of Technology, Pasadena, CA 91125, USA
Interests: physical chemistry at the air-water interface; tropospheric and stratospheric chemistry; gas-liquid reactions

Special Issue Information

Dear Colleagues,

Interfacial water is not thin ‘water’. In the steep water density gradient present at the air–water interface (AWI), extreme anisotropy coexists with a hydrogen-bonding network constrained by the lack of inversion symmetry. These features give rise to unprecedented, unanticipated and often unimagined phenomena from what we know about bulk water. The composition of interfacial layers can also be very different from that of the bulk solutions beneath. The fascinating physical chemistry associated with these observations, however, will be not just another frontier research topic because it matters to what happens on the aerial surfaces of lungs, oceans, clouds and atmospheric aerosols. Understanding what determines the interfacial propensities of ions and molecules, how the interfacial hydrogen-bonding network mediates specific interactions between distant solutes, and how decreased hydration influences equilibria, reactivity and selectivity at the AWI are some of the outstanding issues in this field. Awareness that the AWI may appear different when probed from above and below the surface should inform the conclusions derived from future experiments. Approaches based on molecular dynamic calculations should deal with and possibly account for the collective, long-range interactions apparent in both bulk and interfacial water. Fundamental new concepts are likely to emerge from these studies.

Prof. Dr. Agustin J. Colussi
Guest Editor

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Keywords

  • Non-linear surface spectroscopy
  • Online electrospray ionization mass spectrometry
  • Cooperative effects in water
  • Hydrogen bonding in interfacial water
  • Interfacial atmospheric chemistry
  • Interfacial chemistry of lung epithelial fluids
  • Chemical equilibria in interfacial water
  • Ion hydration in interfacial water

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Published Papers (5 papers)

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Research

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17 pages, 652 KiB  
Article
Biogeochemical Equation of State for the Sea-Air Interface
by Scott Elliott, Zachary Menzo, Amadini Jayasinghe, Heather C. Allen, Oluwaseun Ogunro, Georgina Gibson, Forrest Hoffman and Oliver Wingenter
Atmosphere 2019, 10(5), 230; https://doi.org/10.3390/atmos10050230 - 30 Apr 2019
Cited by 7 | Viewed by 3087
Abstract
We have recently argued that marine interfacial surface tension must have a distinctive biogeography because it is mediated by fresh surfactant macromolecules released locally through the food web. Here we begin the process of quantification for associated climate flux implications. A low dimensionality [...] Read more.
We have recently argued that marine interfacial surface tension must have a distinctive biogeography because it is mediated by fresh surfactant macromolecules released locally through the food web. Here we begin the process of quantification for associated climate flux implications. A low dimensionality (planar) equation of state is invoked at the global scale as our main analysis tool. For the reader’s convenience, fundamental surfactant physical chemistry principles are reviewed first, as they pertain to tangential forces that may alter oceanic eddy, ripple, and bubble fields. A model Prandtl (neutral) wind stress regime is defined for demonstration purposes. It is given the usual dependence on roughness, but then in turn on the tension reduction quantity known as surface pressure. This captures the main net influences of biology and detrital organics on global microlayer physics. Based on well-established surrogate species, tangent pressures are related to distributed ecodynamics as reflected by the current marine systems science knowledge base. Reductions to momentum and related heat-vapor exchange plus gas and salt transfer are estimated and placed on a coarse biogeographic grid. High primary production situations appear to strongly control all types of transfer, whether seasonally or regionally. Classic chemical oceanographic data on boundary state composition and behaviors are well reproduced, and there is a high degree of consistency with conventional micrometeorological wisdom. But although our initial best guesses are quite revealing, coordinated laboratory and field experiments will be required to confirm the broad hypotheses even partially. We note that if the concepts have large scale validity, they are super-Gaian. Biological control over key planetary climate-transfer modes may be accomplished through just a single rapidly renewed organic monolayer. Full article
(This article belongs to the Special Issue Physical Chemistry of the Air-Water Interface)
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19 pages, 6132 KiB  
Article
Night-Time Oxidation of a Monolayer Model for the Air–Water Interface of Marine Aerosols—A Study by Simultaneous Neutron Reflectometry and in Situ Infra-Red Reflection Absorption Spectroscopy (IRRAS)
by Ben Woden, Maximilian W. A. Skoda, Matthew Hagreen and Christian Pfrang
Atmosphere 2018, 9(12), 471; https://doi.org/10.3390/atmos9120471 - 30 Nov 2018
Cited by 13 | Viewed by 4006
Abstract
This paper describes experiments on the ageing of a monolayer model for the air–water interface of marine aerosols composed of a typical glycolipid, galactocerebroside (GCB). Lipopolysaccharides have been observed in marine aerosols, and GCB is used as a proxy for these more complex [...] Read more.
This paper describes experiments on the ageing of a monolayer model for the air–water interface of marine aerosols composed of a typical glycolipid, galactocerebroside (GCB). Lipopolysaccharides have been observed in marine aerosols, and GCB is used as a proxy for these more complex lipopolysaccharides. GCB monolayers are investigated as pure films, as mixed films with palmitic acid, which is abundant in marine aerosols and forms a stable attractively mixed film with GCB, particularly with divalent salts present in the subphase, and as mixed films with palmitoleic acid, an unsaturated analogue of palmitic acid. Such mixed films are more realistic models of atmospheric aerosols than simpler single-component systems. Neutron reflectometry (NR) has been combined in situ with Fourier transform infra-red reflection absorption spectroscopy (IRRAS) in a pioneering analysis and reaction setup designed by us specifically to study mixed organic monolayers at the air–water interface. The two techniques in combination allow for more sophisticated observation of multi-component monolayers than has previously been possible. The structure at the air–water interface was also investigated by complementary Brewster angle microscopy (BAM). This study looks specifically at the oxidation of the organic films by nitrate radicals (NO3•), the key atmospheric oxidant present at night. We conclude that NO3• oxidation cannot fully remove a cerebroside monolayer from the surface on atmospherically relevant timescales, leaving its saturated tail at the interface. This is true for pure and salt water subphases, as well as for single- and two-component films. The behaviour of the unsaturated tail section of the molecule is more variable and is affected by interactions with co-deposited species. Most surprisingly, we found that the presence of CaCl2 in the subphase extends the lifetime of the unsaturated tail substantially—a new explanation for longer residence times of materials in the atmosphere compared to lifetimes based on laboratory studies of simplified model systems. It is thus likely that aerosols produced from the sea-surface microlayer at night will remain covered in surfactant molecules on atmospherically relevant timescales with impact on the droplet’s surface tension and on the transport of chemical species across the air–water interface. Full article
(This article belongs to the Special Issue Physical Chemistry of the Air-Water Interface)
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16 pages, 2659 KiB  
Article
Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface
by Simone Pezzotti and Marie-Pierre Gaigeot
Atmosphere 2018, 9(10), 396; https://doi.org/10.3390/atmos9100396 - 11 Oct 2018
Cited by 19 | Viewed by 4061
Abstract
The knowledge of the water structure at the interface with the air in acidic pH conditions is of utmost importance for chemistry in the atmosphere. We shed light on the acidic air-water (AW) interfacial structure by DFT-MD simulations of the interface containing one [...] Read more.
The knowledge of the water structure at the interface with the air in acidic pH conditions is of utmost importance for chemistry in the atmosphere. We shed light on the acidic air-water (AW) interfacial structure by DFT-MD simulations of the interface containing one hydronium ion coupled with theoretical SFG (Sum Frequency Generation) spectroscopy. The interpretation of SFG spectra at charged interfaces requires a deconvolution of the signal into BIL (Binding Interfacial Layer) and DL (Diffuse Layer) SFG contributions, which is achieved here, and hence reveals that even though H 3 O + has a chaotropic effect on the BIL water structure (by weakening the 2D-HBond-Network observed at the neat air-water interface) it has no direct probing in SFG spectroscopy. The changes observed experimentally in the SFG of the acidic AW interface from the SFG at the neat AW are shown here to be solely due to the DL-SFG contribution to the spectroscopy. Such BIL-SFG and DL-SFG deconvolution rationalizes the experimental SFG data in the literature, while the hydronium chaotropic effect on the water 2D-HBond-Network in the BIL can be put in perspective of the decrease in surface tension at acidic AW interfaces. Full article
(This article belongs to the Special Issue Physical Chemistry of the Air-Water Interface)
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18 pages, 2005 KiB  
Article
The FuGas 2.3 Framework for Atmosphere–Ocean Coupling: Comparing Algorithms for the Estimation of Solubilities and Gas Fluxes
by Vasco M. N. C. S. Vieira, Pavel Jurus, Emanuela Clementi and Marcos Mateus
Atmosphere 2018, 9(8), 310; https://doi.org/10.3390/atmos9080310 - 9 Aug 2018
Cited by 3 | Viewed by 3543
Abstract
Accurate estimates of the atmosphere–ocean fluxes of greenhouse gases and dimethyl sulphide (DMS) have great importance in climate change models. A significant part of these fluxes occur at the coastal ocean which, although much smaller than the open ocean, have more heterogeneous conditions. [...] Read more.
Accurate estimates of the atmosphere–ocean fluxes of greenhouse gases and dimethyl sulphide (DMS) have great importance in climate change models. A significant part of these fluxes occur at the coastal ocean which, although much smaller than the open ocean, have more heterogeneous conditions. Hence, Earth System Modelling (ESM) requires representing the oceans at finer resolutions which, in turn, requires better descriptions of the chemical, physical and biological processes. The standard formulations for the solubilities and gas transfer velocities across air–water surfaces are 36 and 24 years old, and new alternatives have emerged. We have developed a framework combining the related geophysical processes and choosing from alternative formulations with different degrees of complexity. The framework was tested with fine resolution data from the European coastal ocean. Although the benchmark and alternative solubility formulations generally agreed well, their minor divergences yielded differences of up to 5.8% for CH4 dissolved at the ocean surface. The transfer velocities differ strongly (often more than 100%), a consequence of the benchmark empirical wind-based formulation disregarding significant factors that were included in the alternatives. We conclude that ESM requires more comprehensive simulations of atmosphere–ocean interactions, and that further calibration and validation is needed for the formulations to be able to reproduce it. We propose this framework as a basis to update with formulations for processes specific to the air–water boundary, such as the presence of surfactants, rain, the hydration reaction or biological activity. Full article
(This article belongs to the Special Issue Physical Chemistry of the Air-Water Interface)
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Review

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15 pages, 601 KiB  
Review
Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry
by Agustín J. Colussi and Shinichi Enami
Atmosphere 2019, 10(2), 47; https://doi.org/10.3390/atmos10020047 - 26 Jan 2019
Cited by 23 | Viewed by 4529
Abstract
One of the research priorities in atmospheric chemistry is to advance our understanding of heterogeneous reactions and their effect on the composition of the troposphere. Chemistry on aqueous surfaces is particularly important because of their ubiquity and expanse. They range from the surfaces [...] Read more.
One of the research priorities in atmospheric chemistry is to advance our understanding of heterogeneous reactions and their effect on the composition of the troposphere. Chemistry on aqueous surfaces is particularly important because of their ubiquity and expanse. They range from the surfaces of oceans (360 million km2), cloud and aerosol drops (estimated at ~10 trillion km2) to the fluid lining the human lung (~150 m2). Typically, ambient air contains reactive gases that may affect human health, influence climate and participate in biogeochemical cycles. Despite their importance, atmospheric reactions between gases and solutes on aqueous surfaces are not well understood and, as a result, generally overlooked. New, surface-specific techniques are required that detect and identify the intermediates and products of such reactions as they happen on liquids. This is a tall order because genuine interfacial reactions are faster than mass diffusion into bulk liquids, and may produce novel species in low concentrations. Herein, we review evidence that validates online pneumatic ionization mass spectrometry of liquid microjets exposed to reactive gases as a technique that meets such requirements. Next, we call attention to results obtained by this approach on reactions of gas-phase ozone, nitrogen dioxide and hydroxyl radicals with various solutes on aqueous surfaces. The overarching conclusion is that the outermost layers of aqueous solutions are unique media, where most equilibria shift and reactions usually proceed along new pathways, and generally faster than in bulk water. That the rates and mechanisms of reactions at air-aqueous interfaces may be different from those in bulk water opens new conceptual frameworks and lines of research, and adds a missing dimension to atmospheric chemistry. Full article
(This article belongs to the Special Issue Physical Chemistry of the Air-Water Interface)
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