Abstract
Carbonyl sulfide (COS) and other trace gases were measured in firn air collected near South Pole (89.98°S) and from air trapped in ice at Siple Dome, Antarctica (81.65°S). The results, when considered with ambient air data and previous ice core measurements, provide further evidence that atmospheric mixing ratios of COS over Antarctica between 1650 and 1850 A.D. were substantially lower than those observed today. Specifically, the results suggest annual mean COS mixing ratios between 300 and 400 pmol mol−1 (ppt) during 1650–1850 A.D. and increases throughout most of the twentieth century. Measurements of COS in modern air and in the upper layers of the firn at South Pole indicate ambient, annual mean mixing ratios between 480 and 490 ppt with substantial seasonal variations. Peak mixing ratios are observed during austral summer in ambient air at South Pole and Cape Grim, Tasmania (40.41°S). Provided COS is not produced or destroyed in firn, these results also suggest that atmospheric COS mixing ratios have decreased 60–90 ppt (10–16%) since the 1980s in high latitudes of the Southern Hemisphere. The history derived for atmospheric mixing ratios of COS in the Southern Hemisphere since 1850 is closely related to historical anthropogenic sulfur emissions. The fraction of anthropogenic sulfur emissions released as COS (directly or indirectly) needed to explain the secular changes in atmospheric COS over this period is 0.3–0.6%.
Highlights
[2] Carbonyl sulfide (COS) is a long-lived trace gas that is believed to contribute sulfur to the stratospheric aerosol layer [Crutzen, 1976; Chin and Davis, 1995; Ko et al, 2003]
Their results suggested fairly constant COS mixing ratios during the early to mid twentieth century in both hemispheres, in the oldest samples they collected in the Southern Hemisphere (SH) COS was as much as 60 pmol molÀ1 lower than the 480 ppt measured at the surface
COSb COS,b CO2,e d15N of N2e COSb glass flasks and three Al cylinders paired glass flasks not applicable paired glass and stainless steel (Tasmania only) flasks aAir was sampled with the inflatable bladder technique described by Schwander et al [1993] and Battle et al [1996]. bAdditional gases were measured in these samples but are not considered here (CH4, CO, N2O, SF6, chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, chlorinated solvents, methyl halides, halons, and benzene). cAir was sampled from eight permanent tubes installed in January of 1998 [Severinghaus et al, 2001]. dCOS ice core measurements from 82.3 to 90.7 m were published previously by Aydin et al [2002]. eCompounds were used in the modeling of Siple Dome firn; data were published previously by Butler et al [1999]
Summary
[2] Carbonyl sulfide (COS) is a long-lived trace gas that is believed to contribute sulfur to the stratospheric aerosol layer [Crutzen, 1976; Chin and Davis, 1995; Ko et al, 2003]. [5] Aydin et al [2002] reported the first measurements of COS in air from an Antarctic ice core They found COS mixing ratios of 373 ± 37 ppt during 1616 – 1694 A.D. in Antarctica, about 23% lower than observed in the modern atmosphere. [6] Here we report additional measurements of COS from Antarctic firn and ice that supplement published ice and firn atmospheric histories They provide further evidence for substantially lower atmospheric mixing ratios of COS during preindustrial times and suggest substantial declines during recent years in the SH atmosphere
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