Kinetics of Heterogeneous Reaction of H₂O₂ and SO₂ on Coal Fly Ash: Temperature Effect and Their Synergistic Effects

Coal-derived fly ash is a major aerosol composition in the atmosphere and presents a major challenge in understanding the atmospheric environment. In this study, the heterogeneous uptake of hydrogen peroxide and sulfur dioxide on coal fly ash was investigated using a Knudsen cell reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial mixing ratio of H₂O₂ and SO₂ from 10 to 60 ppbv, and the temperature dependence of the uptake coefficients was also carried out over a range from 253 to 313 K. The mixing ratio of H₂O₂ and SO₂ showed little effect on the uptake coefficients for these heterogeneous processes. As a function of temperature, the initial uptake coefficients of H₂O₂ and SO₂ on coal fly ash were (0.48–1.65) × 10⁻⁴ and (1.50–8.54) × 10⁻⁵, respectively, which decreased with an increase in temperature. The steady-state uptake coefficients of H₂O₂ on coal fly ash were in the range of 2.46 × 10⁻⁵ to 4.84 × 10⁻⁵, which increased with an increase in temperature. Furthermore, we examined the synergistic effects between SO₂ and H₂O₂ in their reaction on coal fly ash and found the existence of gaseous H₂O₂ appeared to enhance the ability of SO₂ uptake on coal fly ash. Therefore, this finding suggests that the oxidation of SO₂ on the surface of coal fly ash by gaseous H₂O₂ would promote SO₂ consumption and transformation.