Interaction of peroxynitric acid with solid H 2 O ice

The uptake of peroxynitric acid (PNA), HO 2 NO 2 or HNO 4 , on solid H 2 O 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 2 O 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.