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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 22 | Copyright
Atmos. Chem. Phys., 17, 14025-14037, 2017
https://doi.org/10.5194/acp-17-14025-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 24 Nov 2017

Research article | 24 Nov 2017

Electrospray surface-enhanced Raman spectroscopy (ES-SERS) for probing surface chemical compositions of atmospherically relevant particles

Masao Gen and Chak K. Chan Masao Gen and Chak K. Chan
  • School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China

Abstract. We present electrospray surface-enhanced Raman spectroscopy (ES-SERS) as a new approach to measuring the surface chemical compositions of atmospherically relevant particles. The surface-sensitive SERS is realized by electrospraying Ag nanoparticle aerosols over analyte particles. Spectral features at v(SO42−), v(C–H) and v(O–H) modes were observed from the normal Raman and SERS measurements of laboratory-generated supermicron particles of ammonium sulfate (AS), AS mixed with succinic acid (ASSA) and AS mixed with sucrose (ASsucrose). SERS measurements showed strong interaction (or chemisorption) between Ag nanoparticles and surface aqueous sulfate [SO42−] with [SO42−]AS ∕ sucrose > [SO42−]AS ∕ SA > [SO42−]AS. Enhanced spectra of the solid AS and ASSA particles revealed the formation of surface-adsorbed water on their surfaces at 60% relative humidity. These observations of surface aqueous sulfate and adsorbed water demonstrate a possible role of surface-adsorbed water in facilitating the dissolution of sulfate from the bulk phase into its water layer(s). Submicron ambient aerosol particles collected in Hong Kong exhibited non-enhanced features of black carbon and enhanced features of sulfate and organic matter (carbonyl group), indicating an enrichment of sulfate and organic matter on the particle surface.

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We propose electrospray-surface enhanced Raman spectroscopy (ES-SERS) for measuring the surface chemical compositions of atmospherically relevant particles. The observations of surface aqueous sulfate and adsorbed water demonstrate a possible role of the water in facilitating the dissolution of sulfate from the bulk phase into its water layers. ES-SERS of submicron ambient aerosol particles collected in Hong Kong indicated an enrichment of sulfate and organic matter on the particle surface.
We propose electrospray-surface enhanced Raman spectroscopy (ES-SERS) for measuring the surface...
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