Search for hydrogen peroxide in the martian atmosphere by the planetary fourier spectrometer onboard mars express

We searched for hydrogen peroxide (H₂O₂) in the Martian atmosphere using data measured by the Planetary Fourier Spectrometer (PFS) onboard Mars Express during five martian years (MY27-31). It is well known that H₂O₂ plays a key role in the oxidizing capacity of the Martian atmosphere. However, only a few studies based on ground-based observations can be found in the literature. Here, we performed the first analysis of H₂O₂ using long-term measurements by a spacecraft-borne instrument. We used the ν₄ band of H₂O₂ in the spectral range between 359cm^-1 and 382cm^-1 where strong features of H₂O₂ are present around 362cm^-1 and 379cm^-1. Since the features were expected to be very weak even at the strong band, sensitive data calibrations were performed and a large number of spectra were selected and averaged. We made three averaged spectra for different seasons over relatively low latitudes (50°S-50°N). We found features of H₂O₂ at 379cm^-1, whereas no clear features were detected at 362cm^-1 due to large amounts of uncertainty in the data. The derived mixing ratios of H₂O₂ were close to the detection limits: 16±19ppb at Ls=0-120°, 35±32ppb at Ls=120-240°, and 41±28ppb at Ls=240-360°. The retrieved value showed the detection of H₂O₂ only for the third seasonal period, and the values in the other periods provided the upper limits. These long-term averaged abundances derived by the PFS generally agreed with the ones reported by ground-based observations. From our derived mixing ratio of H₂O₂, the lifetime of CH₄ in the Martian atmosphere is estimated to be several decades in the shortest case. Our results and sporadic detections of CH₄ suggest the presence of strong CH₄ sinks not subject to atmospheric oxidation.