Abstract. The primary chemistry following photolysis of NO3−(aq) and HCOO−(aq) at 200nm is studied by femtosecond spectroscopy using UV and IR techniques supported by electron structure calculations. In the case of NO3−(aq) the dominant primary product is the trans conformer of peroxynitrite, OONO−, whereas the more stable cis conformer is not observed initially. The protonation dynamics of peroxynitrite (a base) is followed in the picosecond region and is well described by the Smoluchowski equation. O−(aq) is observed in the case of HCOO−(aq), but the balancing fragment, CHO(aq) is absent, which likely indicates that it reacts with the aqueous solvent in less than a picosecond. The solid state reactions take place in a sealed reaction chamber of glass or brass. Magnetite [Fe3O4(s)] or pyrite [FeS2(s)] is placed in the chamber which is exposed to gentle mechanical agitation. After several weeks of agitation X-ray diffraction and Mössbauer spectroscopy on the sample show an oxidation of magnetite to hematite [Fe2O3(s)] and of pyrite to [FeSO4(s)]. These findings offer an explanation for the reddish color of Mars and the presence of sulphates in the North Polar Region of Mars.