Attempts have been made to analyse H2O2 and HCHO conserved insurface snow and shallow firn cores in both polar regions regarding theirconcentrations in ancient atmospheres. However, recent fieldmeasurements at several polar locations have demonstrated that anactive photochemistry takes place in the top layers of the surface snowinfluencing not only trace gas concentrations in the boundary layerabove the snow, but also concentrations of several compounds presentin the snow. Since H2O2 and HCHO undergo effective photochemicaldestruction in the gas phase, it can be assumed that both can also bedestroyed if they are present in the surface snow. Here we reportresults of laboratory experiments performed to quantify thephotochemical destruction of H2O2 and HCHO in snow. In closedchambers artificial snow samples containing H2O2 and HCHO wereexposed to high radiation intensities in the UV and visible range. Aneffective decay of H2O2 and HCHO has been observed in allexperiments. Attempts are made to calculate decay rates for bothcompounds in natural surface snow layers. The significance of theseprocesses for the interpretation of H2O2 and HCHO concentrations innatural snow regarding ancient atmospheric concentrations is discussed.