Investigation on Reaction Mechanism of Yellow Sand Particles with Several Air Pollutants

To investigate the heterogeneous uptake of SO2 by yellow sand (China loess, Kosa) particles, we used a cylindrical flow reactor to evaluate the deposition of SO2 onto yellow sand particles. The reactor, which was developed in our laboratory, permits us to vary experimental conditions (e.g., flow rate, gas concentration, relative humidity [R.H.]), and because the gas flow in the reactor was laminar, so that we could evaluate only the SO2 deposition that was due to the diffusion of SO2 molecules in the reactor.Exposure experiments of yellow sand particles to SO2 and HF were performed by the above reactor. The deposition velocities in the exposure to single component gas were compared with those in the exposure to mixed gas.It can be considered that the competitive depositions of SO2 and HF would occur in the latter exposure.The SO2 uptake coefficient depended on relative humidity. These marked changes at R.H. = 60% were probably caused by the formation of a bulk water film on the yellow sand particles; the formation of the water film substantially changed the properties of the mineral dust surface. An SO2 uptake coefficient that takes R.H. into consideration should be used in atmospheric models to predict the dynamics of the interaction between yellow sand particles and SO2