A Mechanism Observation On The Photochemical Reaction Between SO₂ And Atmospheric Aerosol

SO₂ is one of the principal sulfur-containing anthropogenic pollutants, whose oxidation leads to acid rain, its transport and transformation is thus a subject of great environmental interests. Nearly half of the global emissions of SO₂ are converted to particulate sulfate, and this sulfate is often associated with particles, either sea salts over the ocean or mineral dust over the continent. Among the most important natural particles are mineral particles and sea salts. In the past, the heterogeneous oxidation of SO₂ on aerosol particles has been studied extensively using a variety of techniques. However, less kinetic data are available on the uptake of SO₂ on the aerosol particles under light irradiation, which is crucial in understanding the role of aerosol particles in global sulfur-circle and heterogeneous chemistry.Combined with Scanning Electronic Microscopy(SEM), X-ray Fluorescence analyzer (XRF) and Ion Chromatogram(IC), the attempt has been done to observe photochemical oxidation of gaseous SO₂ on aerosol particles using an in suit diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) and White cell.Firstly, the photochemical oxidation of gaseous SO₂ onα-Fe₂O₃ was studied using DRIFTS. The results revealed that SO₂ could be oxidized to form sulfate on the surface ofα-Fe₂O₃ both under light irradiation and in the dark. However, the rate and quantity of sulfate are different. The quantity of sulfate under solar irradiation is slightly less than the one in the dark.Secondly, the photochemical oxidation of the gaseous SO₂ on hematite (α-Fe₂O₃)-NaCl mixtures was studied using DRIFTS. The results revealed that the sample containing 70% of NaCl (w/w) presented the highestγ_BET value under light irradiation, which increased by a factor of 1.48 compared to that of sample in the dark. In the case, the solar irradiation was showed an enhanced reactivity for SO₂ uptake.Finally, the photochemical oxidation reaction of the gaseous SO₂ on typical oxides (SiO₂,Al₂O₃,CaO,MgO)/China loess - NaCl mixtures was studied. The outline described here indicated that real aerosols containing mineral dust and sea-salt in the atmosphere could serve as an efficient scavenger of SO2, and promote significantly the formation of sulfate. But theγ_BET value under the real aerosol was lower by a factor of 1-3 than the value of the typical oxides (SiO₂, Al₂O₃,α-Fe₂O₃, CaO, MgO).