Trend evolution of carbonyl sulfide above Jungfraujoch deduced from ground-based FTIR and ACE-FTS satellite observations

Carbonyl sulfide (OCS) is the most abundant sulfur-containing trace gas in the atmosphere and accounts for a substantial portion of the sulfur in the stratospheric aerosol layer which influences the Earth’s radiation budget and stratospheric ozone chemistry. There remain large uncertainties on some components strengths of the atmospheric OCS budget and on the OCS contribution for sustaining the Stratospheric Sulfate Aerosol (SSA) layer at background levels during quiet volcanic periods.

Monitoring OCS trends can help improving our knowledge about these uncertainties. Using the SFIT-2 algorithm to retrieve atmospheric abundance of OCS from high-resolution ground-based infrared solar spectra recorded on a regular basis with a Fourier Transform Infrared spectrometer (FTIR), under clear-sky conditions, at the NDACC site (Network for the Detection of Atmospheric Composition Change, http://www.ndacc.org) of the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580m asl), we have produced an updated OCS long-term trend from 1995 to 2011, representative for both the troposphere and stratosphere at northern mid-latitudes.

In this contribution, we present and critically discuss the recent OCS trend evolution, in particular the end of the slow decline of its abundance observed in 2002 and the maximum reached in 2008. Comparisons with in-situ measurements in a comparable site and with ACE-FTS satellite observations are in good agreement. They confirm the tropospheric nature of the OCS evolution and suggest that OCS is probably not the main contributor of the SSA layer background level. Some potential anthropogenic causes are also discussed, as aluminium production and coal combustion in China.