A long-term record of carbonyl sulfide (COS) in two hemispheres from firn air measurements

Carbonyl sulfide (COS) was measured in polar firn air from one Arctic and t wo Antarctic locations. The air samples represent atmospheric composition f rom the early to mid-20th century up to the present day. This provides the longest record to date of atmospheric COS. Southern Hemispheric (SH) concen trations appear to have been almost constant at 482 +/- 13 ppt over this pe riod, apart from a slight rise in the earliest part of the record. Northern Hemispheric (NH) concentrations also showed relatively little variation wi th a mean of 525 +/- 17 ppt. Over the last ten years, however, NH concentra tions appear to have declined by about 8 +/- 5%. Such a decline might be du e to decreased carbon disulfide (CS2) emissions by the viscose-rayon indust ry. The absence of any large trend in COS concentrations over the last fift y or more years argues against COS being the origin of reported increases i n stratospheric sulfate aerosol.