The role of carbonyl sulphide as a source of stratospheric sulphate aerosol and its impact on climate 1Atmospheric Chemistry Department, Max-Planck-Institute for Chemistry, Mainz, Germany
01 Feb 2012
2Institute for Physics of the Atmosphere, Johannes Gutenberg University, Mainz, Germany
3The Cyprus Institute, Nicosia, Cyprus, and King Saud University, Riyadh, Saudi Arabia
Received: 09 June 2011 – Published in Atmos. Chem. Phys. Discuss.: 22 July 2011 Abstract. Globally, carbonyl sulphide (COS) is the most abundant sulphur gas in the atmosphere.
Our chemistry-climate model (CCM) of the lower and middle atmosphere with
aerosol module realistically simulates the background stratospheric sulphur
cycle, as observed by satellites in volcanically quiescent periods. The model
results indicate that upward transport of COS from the troposphere largely
controls the sulphur budget and the aerosol loading of the background
stratosphere. This differs from most previous studies which indicated that
short-lived sulphur gases are also important. The model realistically
simulates the modulation of the particulate and gaseous sulphur abundance in
the stratosphere by the quasi-biennial oscillation (QBO). In the lowermost
stratosphere organic carbon aerosol contributes significantly to extinction.
Further, using a chemical radiative convective model and recent spectra, we
compute that the direct radiative forcing efficiency by 1 kg of COS is 724
times that of 1 kg CO2. Considering an anthropogenic fraction of 30%
(derived from ice core data), this translates into an overall direct
radiative forcing by COS of 0.003 W m−2. The direct global warming
potentials of COS over time horizons of 20 and 100 yr are
GWP(20 yr) = 97 and GWP(100 yr) = 27, respectively (by mass).
Furthermore, stratospheric aerosol particles produced by the photolysis of
COS (chemical feedback) contribute to a negative direct solar radiative
forcing, which in the CCM amounts to −0.007 W m−2 at the top of the
atmosphere for the anthropogenic fraction, more than two times the direct
warming forcing of COS. Considering that the lifetime of COS is twice that of
stratospheric aerosols the warming and cooling tendencies approximately
Revised: 19 January 2012 – Accepted: 23 January 2012 – Published: 01 February 2012
Citation: Brühl, C., Lelieveld, J., Crutzen, P. J., and Tost, H.: The role of carbonyl sulphide as a source of stratospheric sulphate aerosol and its impact on climate, Atmos. Chem. Phys., 12, 1239-1253, doi:10.5194/acp-12-1239-2012, 2012.