Next Article in Journal
Extreme Rainfall and Flooding over Central Kenya Including Nairobi City during the Long-Rains Season 2018: Causes, Predictability, and Potential for Early Warning and Actions
Previous Article in Journal
Effects of Meteorology Nudging in Regional Hydroclimatic Simulations of the Eastern Mediterranean
Previous Article in Special Issue
Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface
Article Menu
Issue 12 (December) cover image

Export Article

Open AccessArticle
Atmosphere 2018, 9(12), 471; https://doi.org/10.3390/atmos9120471

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)

1
Department of Chemistry, University of Reading, Reading, Whiteknights RG6 6AD, UK
2
ISIS Pulsed Neutron and Muon Source, Science and Technology Facilities Council (STFC), Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 OQX, UK
3
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, Edgbaston B15 2TT, UK
*
Author to whom correspondence should be addressed.
Received: 12 September 2018 / Revised: 12 November 2018 / Accepted: 24 November 2018 / Published: 30 November 2018
(This article belongs to the Special Issue Physical Chemistry of the Air-Water Interface)
Full-Text   |   PDF [6132 KB, uploaded 30 November 2018]   |  

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 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. View Full-Text
Keywords: aerosol; monolayer; nitrate radical; cerebroside; palmitic acid; palmitoleic acid; neutron; reflectivity; infra-red; Brewster angle microscopy aerosol; monolayer; nitrate radical; cerebroside; palmitic acid; palmitoleic acid; neutron; reflectivity; infra-red; Brewster angle microscopy
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
SciFeed

Share & Cite This Article

MDPI and ACS Style

Woden, B.; Skoda, M.W.A.; Hagreen, M.; Pfrang, C. 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). Atmosphere 2018, 9, 471.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Atmosphere EISSN 2073-4433 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top