(Invited Presentation) Oxidization of SO2 to sulfate by O3, NO2 and nitrate on the surface of mineral dust particles
Heterogeneous reactions between SO2(50PPM)/O3(50PPM) mixing gas and individual CaCO3, Ca(NO3)2 particles (with the geometric diameter of about 6 to 7 micrometers) under various RH conditions were investigated using Micro-Raman Spectrometry and flow reaction system. Chemical composition and microscopic morphology of the individual particles were determined in situ with Micro-Raman spectrometer during the reactions. Individual CaCO3 particles started reaction with SO2/O3 mixing gas at RH values of 55% and 80%, producing CaSO4. The reactive uptake coefficient (¦ĂSO2) was in the order of 10-7 to 10-8 using the geometric surface area of the individual particles. Individual Ca(NO3)2 particles could react completely with SO2/O3 mixing gas at RH values of ≥ 15%. The product was CaSO4. The reactive uptake coefficient (¦ĂSO2) was in the order of 10-6 to 10-7 using the geometric surface area of the individual particles. The reaction rate increased with the RH. At RH=80%, individual Ca(NO3)2 particles with the geometric diameter of 6 micrometers could react completely with SO2/O3 mixing gas in 480 minutes to produce CaSO4.
Under the same RH and concentration of SO2 and O3, the reaction rate of individual Ca(NO3)2 particles with SO2/O3 mixing gas was much higher than that of individual CaCO3 particles with SO2/O3 mixing gas. Thus the formation of Ca(NO3)2 from CaCO3 particles could accelerate the transform of S(IV) to S(VI) in the atmosphere. The possible gaseous product of the reaction between SO2/O3 mixing gas and Ca(NO3)2 particles was HNO3, indicating the heterogeneous reactions between SO2/O3 mixing gas and Ca(NO3)2 particles were sinks of SO2 and O3 and are a potential source of gaseous HNO3, and might have important impacts on the formation of acid rain and atmospheric oxidizability.