Night-time oxidation at the air–water interface: co-surfactant effects in binary mixtures

Federica Sebastiani, Richard A. Campbell, Christian Pfrang*

*Corresponding author for this work

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The ageing of organic-coated aqueous aerosols at night is investigated by reacting NO3 with binary surfactant mixtures floating on water. The surfactants are oleic acid (OA), methyl oleate (MO) and stearic acid (SA). Deuterated surfactants mixed with hydrogenous surfactants were studied using neutron reflectometry to determine the reaction kinetics of organic two-component monolayers with NO3 at the air–water interface for the first time. We measured the rate coefficients for OA monolayers, mixed with hydrogenous co-surfactant MO or SA to be (3 ± 1) × 10−8 cm2 per molecule per s or (3.6 ± 0.9) × 10−8 cm2 per molecule per s and MO monolayers mixed with hydrogenous co-surfactant OA or SA to be (0.7 ± 0.4) × 10−8 cm2 per molecule per s or (3 ± 1) × 10−8 cm2 per molecule per s. The initial desorption lifetimes of NO3, τd,NO3,1, were 8 ± 3 ns, 14 ± 4 ns, 12 ± 3 ns and 21 ± 10 ns. The approximately doubled desorption lifetime for MO–SA compared to the other mixtures is consistent with a more accessible double bond associated with the larger area per molecule of MO in the presence of SA facilitating NO3 attack. The significantly slower reactive loss of MO–OA compared to a MO monolayer demonstrates that multi-component surfactant mixtures need to be studied in addition to single-component monolayers. Such a retarded decay would cause the residence time to change from ca. 4 to 22 minutes associated with increased transport distances of surfactant species together with any other pollutants that may be protected underneath the surfactant film.
Original languageEnglish
Pages (from-to)1-14
Number of pages14
JournalEnvironmental Science: Atmospheres
Issue number6
Publication statusPublished - 12 Sept 2022

Bibliographical note

Funding Information:
The authors would like to thank Dr Francesco Piscitelli, Dr Ernesto Scoppola and Dr Kunal Rastogi for the help during the night shifts on FIGARO. We would like to thank the Partnership for Soft Condensed Matter for access to the ellipsometer, and the ILL (Grenoble, France) for allocations of beam time on FIGARO. We are grateful for technical support at ILL from Simon Wood. FS is grateful for support from the ILL and the University of Reading in the framework of the NEATNOx studentship. CP thanks NERC (grant number NE/G000883/1) for support.

Publisher Copyright:
© 2022 RSC.

ASJC Scopus subject areas

  • Analytical Chemistry
  • Chemistry (miscellaneous)
  • Environmental Chemistry
  • Pollution


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