Influence Of Heterogeneous Reaction On Mineral Aerosol Optical Propertites

Mineral aerosol, one of main components of atmospheric aerosols (including Al2O3, Fe2O3, SiO2, CaO et al) in the troposphere, can impact the climate system by direct radiative forcing through absorbing and scattering solar and terrestrial radiation in the atmosphere, and act as cloud condensation nuclei (CCN) to indirectly influence the optical property and lifetime of clouds. Mineral aerosol can act as one kind of most activated species to react with SO2 and then change their optical properties and chemical composition etc. The similar reactions of SO2 also occour on the particle surface of mineral-sea salt mixture. Until now, the researches of SO2 heterogeneous reaction with aerosols have been mainly focusing on the reaction mechanism. However, studies on the impacts of SO2 heterogeneous reactions on mineral particle optical properties were limited.Combined with Transmission Electronic Microscopy(TEM), Ion Chromatogram (IC) and theory calculation of optical factors, the attempt was afforted to observe the optical variation and sulfate production of gaseous SO2 conversion on mineral aerosol particles using an in suit diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) and White cell. In addition, the variation of optical properties and sulfate production in the heterogeneous reaction was also simulated under Xe irradiation.Firstly, the variation of optical properties and sulfate production of gaseous SO2 heterogeneous reactions on typical oxides (SiO2,α-Fe2O3, CaO,α-Al2O3) and Iron oxidants(α-Fe2O3,Fe3O4,γ-Fe2O3和α-FeOOH) was studied using DRIFTS. The results revealed that the changes of optical properties and sulfate pruducts were great different for the heterogeneous reactions of SO2 with above oxides. Furthermore, it was approved that the rapid variation of optical coefficients appeared in the infrared band of 800-1300 cm-1 for the heterogeneous reactions of SO2 on different oxides. It was noted that Xe irradiation showed certain restrained effect to the heterogeneous reaction.Secondly, hematite as the representation of mineral aerosol, the variation of optical properties and sulfate production of the gaseous SO2 reacted on hematite (α-Fe2O3) was studied under different conditions of temperature, SO2 and O2 concentrations. The results revealed that optical properties and sulfate production showed an trend of initial increase and final decreasing with the increasing of temperature and O2 concentration, and an increasing trend with SO2 concentration. In addition, optical coefficients and sulfate production performed an evolution of initial increasing, midterm decreasing and final stabilizing.Finally, NaCl/KCl as the representation of sea salts, the variation of optical properties and sulfate production of the gaseous SO2 on hematite (α-Fe2O3)/Chinese loess-KCl/NaCl mixtures was studied. The results revealed that optical properties and sulfate production showed an trend of initial increasing and final decreasing with the increasing of NaCl/KCl mass fraction in the mixtures of a-Fe2O3-NaCl andα-Fe2O3-KCl. Optical coefficients and sulfate production of SO2 reacted on the Chinese loess were much larger under Xe irradiation than no Xe irradiation, and it was opposite for the SO2 reaction on the mixtures of Chinese loess-NaCl. This also revealed that Xe irradiation restrained the heterogeneous reactions of SO2 on of China loess-NaCl mixtures.