Heterogeneous reactions of SO2 and NO2 on carbonaceous surfaces

Abstract

Four different types of carbonaceous material (active carbon, graphitized carbon black, source samples from a power plant and from an urban heating boiler) were exposed to synthetic gas mixtures of SO2 and SO2 + NO2 in sub-ppm ranges at two different relative humidities (60 and 90% r.h.). The interaction of SO2 and NO2 with the carbonaceous materials led to sulfate and to three other products: NO, HONO and NO2−. Formation of NO and NO2− was observed only on active carbon while the other three materials yielded HONO. It was also found that NO2 enhances the deposition of SO2 only on the source sample from the power plant at 60% r.h., whereas the material from the urban heating boiler had no effect both at low and high r.h. The results obtained show that no general statements on the effect of NO2 on the heterogeneous reaction of SO2 on these carbonaceous materials can be made and also that NO2 reactions in the presence of SO2 on carbon-containing surfaces should be considered as a source for the production of HONO in the urban environment.