Carbonyl Sulphide (OCS) Variability with Latitude in the Atmosphere

Carbonyl sulphide (OCS) is an important precursor of sulphate aerosols and consequently a key species in stratospheric ozone depletion. The SPectrometre InfraRouge d'Absorption a Lasers Embarques (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 Qualite de l'Air (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 30 km 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 68 +/- 20 years at polar latitudes and 58 +/- 14 years at tropical latitudes leading to a global stratospheric sink of 49 +/- 14 Gg S y(-1).