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 · 10−22cm³molec.−1s−1) and N2O5 + 2H2O → 2HNO3 + H2O (k2 = 1.8 · 10−39cm6molec.−2s−1) is influenced by wall effects to less than 5%. The importance of the gas‐phase N2O5 hydrolysis in the troposphere is discussed.