The O2 Dayglow Observations with the SPICAM IR Experiment on Mars-Express

Content Provider	Semantic Scholar
Author	Guslyakova, Svetlana A. Fedorova, Anna Korablev, Oleg Montmessin, Franck Lefêvre, Franck
Copyright Year	2011
Abstract	Introduction: Ozone is one of the most chemically reactive species of the Martian atmosphere. Study of temporal and space ozone variability along with water vapor variability is necessary to improve photochemical models which have to explain the CO2 atmosphere stability phenomenon. The point is that solar UV radiation dissociates CO2 into CO and O, but their recombination is a very slow process in comparison with O recombination into O2. So, O2 and CO concentrations are expected to be higher than those that were measured. A stably high CO2 concentration maintenance is associated with a chemistry involving “odd hydrogen” species (H, OH, HO2...), as OH can easily react with CO, thus forming CO2 [1]. These “odd hydrogen” species, with the exception of H2O2, had not been directly observed yet. As is known, O3 can be destroyed by odd hydrogen thereby it can be a sensitive tracer to HOx species. Observations: The SPICAM IR spectrometer onboard Mars express mission, launched in 2003, is capable to measure ozone concentration in the Martian atmosphere using observations of O2 molecule emission at 1.27 μm [2]. It covers the spectral range of 1-1.7 μm with spectral resolution of 0.5-1.2nm. The field of view of the spectrometer in the nadir-limb mode is 1° that corresponds to 15-100 km for limb observations depending on the distance to limb and ~5 km near the pericenter in nadir. In this work we present results of limb and nadir observations of the O2 emission and vertical retrieval of ozone profile based on SPICAM IR data. In the limb observation mode spacecraft scans a disc of the planet, its orientation remaining in an inertial attitude. From January 2004 to April 2010 there were made about 600 limb observations in IR range, but only 105 of them were analyzed, as most part of observations were made as a full spectrum with a low sampling. In case of nadir all dataset from 2004 to 2010 has been analyzed. O3 photolisys: Ozone can photodissociate in the following reactions: O3+hν→O(D)+O2(aΔg) (1) O3+hν→ O(P)+O2(ΧΣg) (2). The effectivity of the first reaction is equal to 90%. Photodissociation rate coefficient depends on the solar flux value, solar zenith angle, temperature [3]. For the radiative lifetime we have used the value τ = 4566s [4]. Excited O2 molecule can be deactivated through emission: O2(aΔg)→O2(ΧΣg)+hν (3) or collision: and O2(aΔg)+CO2→O2(ΧΣg)+CO2. (4) Emission (3) occurs at the wavelength 1.27μm and 1.58μm, though the second is 45 weaker while being measured in the laboratory. For the rate constant of deactivation through collision with CO2 we have used a value k = 10cm molecules s[5]. The O2 intensity in MR can be expressed as:
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Language	English
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