Interaction of peroxynitric acid with solid H_2O ice

Abstract

The uptake of peroxynitric acid (PNA), HO_2NO_2 or HNO_4, on solid H_2O ice at 193 K (−80°C) was studied using a fast flow‐mass spectrometric technique. An uptake coefficient of 0.15 ± 0.10 was measured, where the quoted uncertainty denotes 2 standard deviations. The uptake process did not result in the production of gas phase products. The composition of the condensed phase was investigated using programmed heating (3 K min^(−1)) of the substrate coupled with mass spectrometric detection of desorbed species. Significant quantities of HNO_4 and HNO_3 desorbed from the substrates at temperatures above 225 K and 246 K, respectively. The desorbed HNO_3, which was less than 9% of the desorbed HNO_4 and remained unchanged upon incubation of the substrate, was likely due to impurities in the HNO_4 samples rather than reaction of HNO_4 on the substrate. The onset temperatures for HNO_4 desorption increased with increasing H_2O to HNO_4 ratios, indicating that HNO_4, like HNO_3, tends to be hydrated in the presence of water. These observations suggest possible mechanisms for removal of HNO_4 or repartitioning of total odd nitrogen species in the Earth's upper troposphere and stratosphere.