Water vapour influence over the PAN stability: Homogeneous and heterogeneous processes between PAN-NO2-H2O

Abstract

The study of the interaction between H2O in gas phase and pollutants has gained great importance to understand the role of water in the atmospheric processes. In this contribution the stability of peroxyacetyl nitrate with water molecules in the gas phase was investigated using experimental and theoretical methods. The temporal variation of PAN concentration was monitored by infrared spectroscopy in the presence of H2O, NO2/H2O and NO/H2O mixtures. The main products observed were: methyl nitrate, carbon dioxide and nitrous acid. There is no evidence of acetic acid formation as was proposed in previous studies. The presence of water increases the rate of PAN disappearance as consequence of NO formation from the NO2 + H2O reaction and heterogeneous processes. Ab-initio calculations were performed to study the interaction between PAN and water molecules. Also, kinetics simulations were used to corroborate the experimental results.