Heterogeneous Reactions Between Airborne Sulfur Containing Compounds With Mineral Oxides And Atmospheric Particles

Atmospheric particles or aerosols play an significant role in atmospheric irradiation balance and changes of chemical components, and many key chemical processes including ozone depletion and acid deposition are known to be concerned with them. Heterogeneous and multiphase reactions on the surface of atmospheric particles are important ways for the production and elimination of atmospheric reactive gases. However, not all of these chemical processes have been known well due to the complexity of gas-phase species, and differences of particle concentrations, surface property and reactivity of condensed-phase species. To obtain more information about these heterogeneous and multiphase processes, it is a routine research approach to investigate the reactions between classified atmospheric trace gases and aerosol particles.Sulfur-containing compounds are the major pollutions in the atmosphere, and mineral dust particles are one of the most active components of aerosols. It is significant to study the heterogeneous reactions between them, for revealing the contribution of atmospheric particles to the conversion of sulfur-containing compounds in the atmosphere.The reaction system based on long optical path FTIR monitoring was established in this work. Combined X-ray Photoelectron Spectroscopy(XPS), in situ Diffused Reflectance Infrared Fourier Transform Spectroscopy(DRIFTS) and Transmission FTIR, the heterogeneous (photo) reactions between sulfur-containing gases, sulfur dioxide(SO₂), carbonyl sulfide(COS) and dimethyl sulfide(DMS), and typical oxides in mineral dust and collected atmospheric particles were investigated, and the reaction mechanisms and kinetics were discussed detailedly in this paper.Firstly, the mechanism of the heterogeneous reaction SO₂/O₂ + Oxides(or particles) was proved to be adsorption of SO₂ on the oxides forming SO₃^2- or HSO₃^2-, and then oxidized into SO₄^2- by hydroxyls and active adsorbed O atoms. The reactivity of different oxides with SO2 was compared, and the apparent reaction rate coefficient of collected atmospheric particles with SO₂ was determined as 2.28×10^-5 s^-1. It can be deduced that the heterogeneous reactions of SO₂ with atmospheric particles may contribute significantly to the conversion of SO₂ in the atmosphere, if the reaction rate coefficient could keep constant under all conditions.