Carbonyl sulfide concentration in the Arctic lowermost stratosphere and stratosphere-troposphere transport

Concentrations of carbonyl sulfide (COS) were measured in whole air samples collected between East Asia (Japan) and the Arctic (Spitsbergen) up to an altitude of 12 km during the Arctic Airborne Measurement Program 98 (AAMP98). Continuously measured O₃ and CO₂ concentrations were used to interpret the distribution of COS concentrations. A latitudinal gradient to lower concentrations of COS was observed poleward of 70°N; concentrations of COS were 421 ± 27 pptv poleward of 70°N and 461 ± 30 pptv at 60-70°N. The relationship between COS concentration and the O₃/CO₂ ratio indicates that the concentrations of COS near the ozonopause were almost equal to those in the troposphere, and then decreased as the O₃/CO₂ ratio increased. Tropospheric influence was observed up to potential temperatures of 350 K in this study. According to the AAMP98 observations, on the basis of the trajectory analysis and the O₃/O₂ ratio, distribution of COS in the Arctic lowermost stratosphere is certainly effected by the downward transport of an arctic stratospheric air mass and by the horizontal transport of a tropospheric air mass across the tropopause over midlatitudes. The sulfate aerosol produced by COS oxidation is estimated to be very small at the observed altitudes between East Asia and the Arctic in late winter.