Atmospheric Carbonyl Sulphide (OCS) measured remotely by FTIR solar absorption spectrometry
Abstract. Atmospheric OCS abundances have been retrieved from spectra measured by the JPL MkIV Fourier Transform Infra-Red (FTIR) spectrometer during 24 balloon flights and during nearly 1100 days of ground-based observations since 1985. Our spectral fitting approach uses broad windows to enhance the precision and robustness of the retrievals. Since OCS has a vertical profile similar in shape to that of N2O, and since tropospheric N2O is very stable, we reference the OCS observations to those of N2O, measured simultaneously in the same airmass, to remove the effects of stratospheric transport, allowing a clearer assessment of secular changes in OCS. Balloon measurements reveal less than 5 % change in stratospheric OCS amounts over the past 25 years. In the troposphere a springtime peak of tropospheric OCS is seen, followed by a rapid early summer decrease, similar to the behavior of CO2. This results in a peak-to-peak seasonal cycle of 5–6 % of the total OCS column at Northern mid-latitudes. In the long-term tropospheric OCS record, a 5 % decrease is seen during 1990–2002, followed by a 5 % increase from 2003 to 2012.