Kinetics and mechanism of the heterogeneous reaction of N2O5 with mineral dust particles

Abstract

The heterogeneous interaction of N₂O₅ with Saharan dust particles was investigated using aerosol flow tubes with detection of N₂O₅ by cavity-ring-down spectroscopy. The uptake coefficient, γ, was determined to be 0.02 ± 0.01 on airborne Saharan dust particles, independent of relative humidity (RH, 0–67%) and initial N₂O₅ concentration (5 × 10¹¹–3 × 10¹³ molecule cm⁻³). Analysis of gas- and particulate phase products suggests that N₂O₅ undergoes heterogeneous hydrolysis forming particulate nitrate. The independence of γ on the initial N₂O₅ concentration indicates that, on the seconds time scale of these experiments, the heterogeneous reaction of N₂O₅ with dust particles is not restricted to the external particle surface but internal reactive sites are also available. The particles could be deactivated with respect to N₂O₅ uptake only when pre-treated with very high levels of HNO₃.