Pascal Jeseck

Carbonyl Sulphide (OCS) Variability with Latitude in the Atmosphere

Abstract Carbonyl sulphide (OCS) is an important precursor of sulphate aerosols and consequently a key species in stratospheric ozone depletion. The SPectromètre InfraRouge dAbsorption à Lasers Embarqués (SPIRALE) and shortwave infrared (SWIR) balloon-borne instruments have flown in the tropics and in the polar Arctic, and ground-based measurements have been performed by the Qualité de lAir (QualAir) Fourier Transform Spectrometer in Paris. Partial and total columns and vertical profiles have been obtained to study OCS variability with altitude, latitude, and season. The annual total column variation in Paris reveals a seasonal variation with a maximum in April–June and a minimum in November–January. Total column measurements above Paris and from SWIR balloon-borne instrument are compared with several MkIV measurements, several Network for the Detection of Atmospheric Composition Change (NDACC) stations, aircraft, ship, and balloon measurements to highlight the OCS total column decrease from tropical to polar latitudes. OCS high-resolution in situ vertical profiles have been measured for the first time in the altitude range between 14 and 30u2005km at tropical and polar latitudes. OCS profiles are compared with Atmospheric Chemistry Experiment (ACE) satellite measurements and show good agreement. Using the correlation between OCS and N2O from SPIRALE, the OCS stratospheric lifetime has been accurately determined. We find a stratospheric lifetime of 68u2009±u200920 years at polar latitudes and 58u2009±u200914 years at tropical latitudes leading to a global stratospheric sink of 49u2009±u200914u2005Ggu2005Su2005y−1.

Mesures spectroscopiques de constituants et de polluants atmosphériques par techniques in situ et à distance, au sol ou embarquées

Resume La spectroscopie infrarouge est un outil puissant pour mesurer precisement les concentrations despeces a letat de trace dans latmosphere par lutilisation des signatures spectrales, caracteristiques des differentes especes moleculaires, qui sont associees aux bandes de vibration–rotation dans linfrarouge moyen ou proche. Differentes methodes basees sur la spectroscopie quantitative permettent de realiser des mesures tropospheriques ou stratospheriques : absorption a long parcours in situ, absorption/emission atmospherique par spectrometrie de Fourier avec des instruments a haute resolution spectrale installes au sol ou embarques a bord davion, sous ballon ou sur satellite.

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

Water is the main constituent of interstellar ices, and it plays a key role in the evolution of many regions of the interstellar medium, from molecular clouds to planet-forming disks1. In cold regions of the interstellar medium, water is expected to be completely frozen out onto the dust grains. Nonetheless, observations indicate the presence of cold water vapour, implying that non-thermal desorption mechanisms are at play. Photodesorption by ultraviolet photons has been proposed to explain these observations2,3, with the support of extensive experimental and theoretical work on ice analogues4–6. In contrast, photodesorption by X-rays, another viable mechanism, has been little studied. The potential of this process to desorb key molecules such as water, intact rather than fragmented or ionized, remains unexplored. We experimentally investigated X-ray photodesorption from water ice, monitoring all desorbing species. We found that desorption of neutral water is efficient, while ion desorption is minor. We derived yields that can be implemented in astrochemical models. These results open up the possibility of taking into account the X-ray photodesorption process in the modelling of protoplanetary disks or X-ray-dominated regions.The X-ray-induced photodesorption of water from astrophysical ices, intact, has been little studied. However, it could be a key process in producing the cold water vapour that is seen in these regions. Here, the yield of such a mechanism is experimentally quantified.