Global Distributions of Carbonyl Sulfide (OCS) in the Upper Troposphere and Stratosphere Michael Barkley & Paul Palmer, University of Edinburgh Chris Boone & Peter Bernath †, University of Waterloo ( † University of York) Parvadha Suntharalingham, UEA & Harvard University

Michael Barkley, University of EdinburghSlide 2 Outline  Introduction ♦ A quick tour of the OCS world - why is OCS important?  ACE retrievals of OCS ♦ What does the raw data tell us?  Validation - comparisons of ACE OCS to other OCS measurements ♦ ACE vs. ATMOS v3 data (Shuttle-borne high res n. FTIR) ♦ ACE vs. MkIV data (Balloon-borne high res n. FTIR)  Global Distributions ♦ Global Maps ♦ Zonal means & latitudinal profiles ♦ Estimate of OCS stratospheric Lifetime  Summary

Michael Barkley, University of EdinburghSlide 3 Why is OCS interesting & important?  Most long-lived and abundant sulphur gas in the atmosphere  OCS oxidised in stratosphere to form sulfate aerosol - which supposedly ‘sustains’ the Stratospheric Sulfate Aerosol layer (SSA) ♦ Attenuation of UV radiation ♦ Surface for heterogeneous chemistry  More recently: uptake of OCS by plants is very similar to uptake of CO 2 ♦ Can OCS constrain GPP/biospheric fluxes of C?  Uncertainty in budget OCS seasonal cycle similar to CO 2

Michael Barkley, University of EdinburghSlide 4 OCS Global Budget CS 2 SO 2 Aerosols Stratosphere Troposphere 41 (154) -130 (56)-238 (30)64 (32) CS 2 DMS 154 (37) 84 (54) 116 (58) 70 (50) Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks SO 2 OCS OCS (~2.5Tg) OCS (~0.3Tg) 0.31Tg0.34Tg ~9% Chin & Davis, JGR, 1995 Flux (error) [Gg S] Atmospheric Losses: OH: -94 (12) O: -11 (5) hv: -16 (5) Tot: -121 (14)

Michael Barkley, University of EdinburghSlide 5 Source/sink seasonal variability  Seasonal cycle determined by: ♦ NH: Vegetation and ocean ♦ SH: Ocean  Sources & sinks drive variability in lower atmosphere Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks Suntharalingham et al, 2008

Michael Barkley, University of EdinburghSlide 6 ACE OCS retrievals  Use improved v2.2 ‘research products’ ♦ More micro-windows & higher altitudes  Uses HITRAN 2004  8 interfering species fitted simultaneously: ♦ OCS ♦ Isotopologue 2 ♦ O 3 ♦ Isotopolgues 1 & 3 ♦ CO 2 ♦ Isotopolgues 1,2,3 & 4 ♦ H 2 O Centre [cm -1 ] Width [cm -1 ] Low-z [km] High-z [km] to 819 to to 1020 to to 1220 to to to 822 to to 823 to to 1823 to to 823 to to 1523 to to 1523 to to 812 to to 812 to 15 Low z = 8 – 2 x [sin(lat)] 2 Fitting windows Pole to Equator

Michael Barkley, University of EdinburghSlide 7 ACE OCS Total # occultations = No data below ~6 km or above ~31 km Few measurements > 600 pptv

Michael Barkley, University of EdinburghSlide 8 ACE vs. MkIV Balloon Profiles MkIV data courtesy of Geoff Toon, JPL, NASA

Michael Barkley, University of EdinburghSlide 9 ACE measurements (not) near Fort Sumner

Michael Barkley, University of EdinburghSlide 10 Comparing ACE to ATMOS: where & when?

Michael Barkley, University of EdinburghSlide 11 ACE vs. ATMOS ATMOS data courtesy of JPL, NASA

Michael Barkley, University of EdinburghSlide 12 Some useful numbers… Differences most likely due to improvements in spectroscopic 5 microns ACE – HITRAN 2004 ATMOS – Atmos line list ATMOS ~ 10% > ACE

Michael Barkley, University of EdinburghSlide 13 ACE OCS Global Distributions ( )

Michael Barkley, University of EdinburghSlide 14 Zonal Seasonal Means Profiles averaged in 15°latitude bins; only bins with a minimum of 10 profiles are plotted. Distributions largely determined by atmospheric transport

Michael Barkley, University of EdinburghSlide 15 Zonal Seasonal Means Profiles averaged in 15°latitude bins; only bins with a minimum of 10 profiles are plotted. HCN CO

Michael Barkley, University of EdinburghSlide 16 Zonal Seasonal Means Profiles averaged in 15°latitude bins; only bins with a minimum of 10 profiles are plotted. Data from: Atlantic cruises + Atlas-3 Notholt et al., Science, 2003

Michael Barkley, University of EdinburghSlide 17 Seasonal Maps at 9.5 km

Michael Barkley, University of EdinburghSlide 18 Seasonal Maps at 9.5 km INTEX-A 1 st July – 14 th August 2004 (Blake et al. 2008)

Michael Barkley, University of EdinburghSlide 19 Mean Latitudinal Profiles

Michael Barkley, University of EdinburghSlide 20 Mean Latitudinal Profiles

Michael Barkley, University of EdinburghSlide 21 OCS stratospheric lifetime  Long-lived trace gases in stratosphere are linearly correlated  provided lifetime of one species is known, the lifetime of the other can be estimated [see Plumb & Ko, 1992] T 1 = T 2 x (dΩ 2 /dΩ 1 ) x (Ω 1 /Ω 2 )  Use coincidental ACE measurements of CFC-11 and CFC-12 + & CFC lifetimes & tropospheric VMRs from the WMO 2006 report: ♦ CFC-11 (CFCl 3 ) ♦ Ω = 254 pptv, T=45±10 yrs ♦ CFC-12 (CF 2 Cl 2 ) ♦ Ω = 540 pptv, T=100±20 yrs  Tropospheric OCS = 500 pptv ♦ Note, don’t use ACE value as it represents UT

Michael Barkley, University of EdinburghSlide 22 Some more useful numbers… Best estimate = 64±21 yrs

Michael Barkley, University of EdinburghSlide 23 What does the stratospheric lifetime tell us?  ‘Back of envelope’ calculation ♦ OCS stratospheric sink = total mass of OCS in atmosphere / stratospheric lifetime  Using the best estimate for OCS lifetime = 64±21 yrs ♦ OCS stratospheric sink = 63 – 124 Gg OCS / yr ♦ = 34 – 66 Gg S / yr  No OCS source in strat s  sink = tropospheric flux  Tropospheric sulfur flux (in the form of OCS) required to sustain the stratospheric sulfate aerosol layer (see Chin and Davis, JGR, 1995 & references therein) ♦ = 30 – 170 Gg S / yr  i.e., our estimate is at the lower end of this range  Answer: Need to re-examine OCS contribution to SSA using ACE data and stratospheric sulfur/aerosol model

Michael Barkley, University of EdinburghSlide 24 What does the stratospheric lifetime tell us?  ‘Back of envelope’ calculation ♦ OCS stratospheric sink = total mass of OCS in atmosphere / stratospheric lifetime  Using the best estimate for OCS lifetime = 64±21 yrs ♦ OCS stratospheric sink = 63 – 124 Gg OCS / yr ♦ = 34 – 66 Gg S / yr  No OCS source in strat s  sink = tropospheric flux  Tropospheric sulfur flux (in the form of OCS) required to sustain the stratospheric sulfate aerosol layer (see Chin and Davis, JGR, 1995 & references therein) ♦ = 30 – 170 Gg S / yr  i.e., our estimate is at the lower end of this range  Answer: Need to re-examine OCS contribution to SSA using ACE data and stratospheric sulfur/aerosol model

Michael Barkley, University of EdinburghSlide 25 Summary  OCS important but large uncertainties in budget remain  ACE has provided the first global OCS UT/stratosphere distributions observed from space ♦ Generally good agreement with other OCS measurements ♦ Distributions governed by atmospheric transport ♦ Biomass burning is a significant source in SH tropics… ♦ …but is it weaker than previously thought?  Strong correlations with CFC-11 & CFC-12 yields: ♦ OCS stratospheric lifetime = 64 ± 21 yrs ♦ OCS stratospheric sink = 63 – 124 Gg OCS / yr  Next step, (someone) must incorporate ACE OCS measurements into global CTM  Results submitted to GRL paper (in revision)

End

Michael Barkley, University of EdinburghSlide 27 ACE vs. Aircraft  GMD NOAA aircraft flights (grey lines) constrained to region: ♦ °N ♦ °W  ACE sampled over: ♦ °N ♦ °W ♦ Necessary to get ACE data down to ~8 km  Construct mean aircraft profile (red line)  Interpolate across altitude gap (if necessary) and smooth (light green line)  First complete trop-strat OCS profiles! Aircraft data courtesy of Stephen Montzka GMD, NOAA

Michael Barkley, University of EdinburghSlide 28 Summary of MkIV and ATMOS instruments  MkIV ♦ Balloon-borne high resolution FTIR ♦ Covers cm -1 spectral region at 0.01 cm -1 resolution ♦ Solar Occultation  ATMOS ♦ Atmospheric Trace Molecule Spectroscopy experiment ♦ Balloon-borne high resolution FTIR ♦ Covers cm -1 spectral region at 0.01 cm -1 resolution ♦ Solar Occultation

Michael Barkley, University of EdinburghSlide 29 Finely balancing the OCS global budget  Total sources = 592 ( ) † [ ] *  Total sinks = 489 ( ) † [ ] * ♦ † = Suntharalingham et al, JGR (sub), 2007 (GEOS-Chem) ♦ * = Montzka et al, JGR, 2007 (Observations + Kettle fluxes) “…within the large associated range of uncertainties..” Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks

Michael Barkley, University of EdinburghSlide 30 Past Variability Sulfur emissions? Deforestation? Viscose rayon production of CS 2 ? Little Ice Age AD Drop not understood Montzka et al., JGR, 2004