Seminar on Physics and Chemistry of the Atmosphere (Abstract)

Photochemical decomposition of nitrate (NO₃-) in artificial snow
 

Emmanuel Quansah
AWI Bremerhaven

09.07.2004, 13.00 c.t.
Room N3380

Photolysis of NO₃- in surface snow has been reported to modify the composition of surface snow, of the interstitial air of surface snow, and the overlying atmosphere.
Therefore, laboratory experiments were performed to investigate the photochemical reaction of NO₃- in artificial snow under natural conditions and to compare NO₃- photolysis with that of hydrogen peroxide (H₂O₂) and formaldehyde (HCHO). For these experiments, artificial snow prepared from purified water containing sodium nitrate was used.
Samples of the snow were irradiated in the UV and visible range, which resulted in the decomposition of the NO₃-. The decomposition followed a first-order decay rate, which suggests photolysis reactions.
The results indicate that the photolysis of NO₃- is comparable to that of H₂O₂ under similar conditions. The analysis of the irradiated samples demonstrated that nitrite (NO₂-) is a product of the NO₃- photolysis in snow. However, a comparison of the lost NO₃- with the produced NO₂- revealed that only a small fraction of the decomposed NO₃- remained as NO₂- in the snow. Most likely, most of the NO₃- is converted into volatile compounds like NO and/or NO₂.
Further experiments with formate (HCOO-) added, with the aim of examining hydroxyl radicals (OH) as possible products of NO₃- photolysis are in progress.