Photochemical Effects in the Heterogeneous Reaction of Soot with Ozone at Low Concentrations

Abstract

The soot-ozone reaction at low concentrations (ppm O3) hasbeen examined todetermine any influence of solar radiation on its products and kinetics. Theeffect of simulatedsolar radiation is to change the product distribution towardsCO2(g), CO (g) and H2O(g) at theexpense of soot surface functional groups formation. Little effect on theextent or rate ofdiminution of O3 through this rapid reaction is observed. Theinitial rate laws for formation ofall products remain the same under simulated solar radiation, with changes inthe rate constants(and thus in the relative importance of mechanistic pathways) responsible forthe differingproduct distributions. Decarboxylation of soot surface functionalities hasbeen shown to be onepossible mechanism underlying these effects. Atmospheric soot, particularlythat emitted nearthe tropopause by increasing numbers of subsonic and supersonic aircraft, mayplay a role inozone depletion; the rapid diminution of ozone in soot's presence isunaffected by solarradiation.