Articles | Volume 17, issue 22
https://doi.org/10.5194/acp-17-14025-2017
https://doi.org/10.5194/acp-17-14025-2017
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

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 (AS ∕ SA) and AS mixed with sucrose (AS ∕ sucrose). 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 AS ∕ SA 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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Short summary
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.
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