Heterogeneous Loss of Gas-Phase Ozone on n-Hexane Soot Surfaces: Similar Kinetics to Loss on Other Chemically Unsaturated Solid Surfaces

The heterogeneous loss of ozone on n-hexane soot surfaces has been studied in a coated-wall flow tube connected to a mass spectrometer for gas-phase analysis. Uptake measurements confirm earlier studies that the initial uptake is primarily noncatalytic and that the number of reactive surface sites is close to that of a full monolayer. The initial uptake kinetics exhibit an inverse dependence on ozone gas-phase concentration, as expected in the surface-saturated limit if the reaction proceeds via a Langmuir-Hinshel wood mechanism. Support for this reaction's not being an Eley-Rideal process comes from the lack of temperature dependence of the initial uptake coefficient from 260 to 360 K and that a saturated surface coverage of adsorbed dodecane does not affect the kinetics. It is demonstrated that there is a strong similarity between the initial uptake kinetics for ozone loss on a wide variety of surfaces, including soot; 1-hexadecene (as studied in this work); metal oxides, including atmospheric mineral dust; and PAHs adsorbed on a variety of surfaces. This suggests that the ozone loss may proceed through a common reaction pathway on such surfaces.