Gas-phase reaction of N2O5 with water vapor: Importance of heterogeneous hydrolysis of N2O5 and surface desorption of HNO3 in a large teflon chamber

Abstract

Laboratory measurements of the gas-phase hydrolysis of N2O5 are always preturbed by wall reactions. Their contribution could be quantified in a large double-walled teflon bag chamber by introducing HNO3 into the chamber and analysing its temporal evolution in the gas-phase at low and high relative humidities, and by varying the surface-to-volume ratio of the chamber. By fitting a model to the experimental results, a consistent set of rate coefficients for adsorption and desorption of HNO3 from the chamber walls could be obtained. The desorption is so slow that the gas-phase hydrolysis of N2O5 via the reactions N2O5 + H2O → 2HNO3 (k1=2.5 · 10-22 cm3molec.-1s-1) and N2O5 + 2H2O → 2HNO3 + H2O (k2=1.8 · 10-39 cm6molec.-2s-1) is influenced by wall effects to less than 5%. The importance of the gas-phase N2O5 hydrolysis in the troposphere is discussed. Copyright 1998 by the American Geophysical Union.