Reactivity of organic sulfur compounds deposited on the surface of sea salts: Influence of humidity and UV-Vis light

L. JUNCAL, L. PICONE, R. M. ROMANO,; S. SENG, A. M. MOREAU, I. DE WAELE, Y. TOBÓN Y S. SOBANSKA

Milán

Conferencia; EAC 2015, European Aerosol Conference; 2015

In this study, laboratory experiments were conducted to simulate heterogeneous reaction at the surface of sea salt particle (NaCl) coated with Methyl thioglycolate (MTG) and exposed to humidity and UV-Vis light. We have used MTG (CH3OC(O)CH2SH) as model of low volatile sulfur compound of industrial or biological origin. Observation of processes occurring on NaCl surfaces was performed by µ-Raman spectroscopy, µ-FT-IR, Atomic Force Microscopy (AFM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The combined use of these techniques is a powerful tool to determine the morphology and the distribution of molecular species, as well as the first layers (few nm) at the surface of particles (Scolaro et al. 2009, Gaspar et al. 2004).MTG deposited on the NaCl (100) surface by evaporation formed micrometric size droplets composed of the disulfide derivative of MTG, identified by both µ-Raman and µ-FTIR.After irradiation with UV-Vis light, formation of sulfate on the surface of NaCl was evidenced at the surface scale. The formation of SO42- was confirmed by ToF-SIMS measurement.The photochemical behavior of sulfur compounds on sea salt surface was investigated by complementary approaches. Experiments showed original and non-expected results with atmospheric interest. The formation of SO42- through the photo-degradation of an organosulfur compound on NaCl surface is for the first time demonstrated. The combination of µ-Raman Spectroscopy, µ-FT-IR, AFM and ToF-SIMS imaging has shown to be a powerful tool for studying the heterogeneous chemistry of the particle surfaces.