GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 4, PAGES 393-396, FEBRUARY 15, 1995 Carbonyl sulfide (COS) measurements in the Arctic polar vortex K.A. Kourtidis •, R. Borchers •, P. Fabian 2,and J. Harnisch • Abstract. One stratospheric carbonyl sulfide (COS) vertical profile in the Arctic polar vortex has been retrieved from air samplescollectedby the MPAE balloon-borne cryogenic sampleron January 18, 1992, at Kiruna, Sweden. The measurements were made in thealtitude range 7.5-28.5 km. The upper tropospheric volume mixing ratios of COS were 355 4- 60 pptv. The stratospheric profile showsthat COS is subject to considerablesubsidence this time of the year. The lowest VMRs were encountered at around 20 km altitude, while above that height a COS increase was observed. A possible explanation could be reversible .uptake of COS by frozen sulfuric acidaerosols. Introduction Carbonyl sulfide (COS) is an ubiquitous constituent of the earth'satmosphere. Its sources are both natural andanthropogenic, the latter being currently estimated as around30% of the total [Chin and Davis, 1993]. The main natural sources are the ocean, where COS is produced through the photooxidation of dissolved or- ganic matter by UV-B radiation[Andreae and Ferek, 1992],and the soils. Other sources include biomass burning, carbon disulfide (CS2)conversion, andvarious anthropogenic processes [Khalil and Rasmussen, 1984; Chin and Davis, 1993; Posand Berresheim, 1993]. Its main sink seems to be uptake by vegetation [Goldan et al., 1988], with other important sinksbeing reac- tion with OH and stratospheric photolysis. The tro- pospheric abundance of COS is around 500 pptv [e.g. Bandy et al., 1992] and its lifetime isestimated as about 2 years [Khalil and Rasmussen, 1984]. It isthus the only sulfur-containing gaswhich is sufficiently long-lived to enter the stratosphere in considerable amounts. Its pho- tooxidation in the stratosphere will produce SO2which will in turn be converted to sulfuric acid and ultimately form sulfate aerosols. It is considered to be the pri- mary contributor to the stratospheric sulfateaerosol layer during volcanic quiescent periods [Crutzen, 197(}]. This highlyvariable layer of particles has its maximum •Max-Planck-Institut ffirAeronomie, Katlenburg-Lindau, Germany 2Ixhrstuhl fOr Biokimatologie und Immissionsforsehung, University of Munich, Germany Copyfight 1995 by theAmerican Geophysical Union. Paper number 94GL03306 0094-8534/95/94GL-03306503.00 at around 18-20 km altitude and can catalyze ozone depletion through heterogenous reactions taking place on the surface of the particles [Hofmann and Solomon, 1989; Rodriguez et al., 1991; Solomon et al., 1993]. It scatterssunlight and thus also influences the radiation budget of the atmosphere [Baldwin et al., 1976]. Verti- cal COS profiles in the stratosphere havebeenreported by various groups. The measuring techniques involved cryogenic sampling [Inn et al., 1981; Leifer,1989], and IR absorption spectroscopy [Louisnard et al., 1983; Zan- der et al., 1988]. COS volume mixingratios havebeen found to vary around 300-600 pptv near the tropopause [Carroll, 1985; Leifer, 1989], decreasing with altitude to about 10-150 pptv at 27 km height [Louisnard et al., 1983; Zander et al., 1988]. Measurements of condensation nuclei (CN) both with- in the Arctic and the Antarctic polar vortex haveshown enhanced concentrations above 20 km [Holmann et al., 1986; Holmann,1990; Wilson et al., 1990], whichwere attributed to condensation of sulfuric acid vapour pro- duced by photooxidation of COS and/or reaction of COS with enhanced OH within the vortex [Oppen- heimer, 1987; Holmann et al., 1989]. COS measure- ments within the polar vortex could help to test the relevance of these mechanisms. The first stratospheric COS vertical profile within the Arctic Polar vortex is presented here, together with someupper tropospheric measurements. Experimental methods The MPAE cryosamplerwas used to take air sam- ples at various altitudes (fromaround 6 km to around 30 km). The cryosampler hasbeen described in detail elsewhere [Fabian, 1981].Briefly, it consists of 15 evac- uated stainless steel tubes submerged in liquid neon. The activation of their remotely-controlled valves en- ables sampling of air at 15 altitudes. After recovery of the cryosampler, the samplesare stored at room tem- perature, and they are analysed in the laboratory by gas chromatography combined with various detectors. The cylinders have a volume of 1.4 lt, and the samples have a pressure of 30-70 bar at room temperature. Ver- tical profiles of many trace gases havebeenretrieved in the past after completion of morethan 20 flights[e.g. Fabian et al., 1985; Borchers et al., 1987; Singh et al., 1988]. The air samples obtained from the 1992flights were analysed for COS by gas chromatographic separa- tion on a temperature-programmed DB-1 capillary col- umn and mass spectrometric detection of COS at m/e 393