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Global Distributions of Carbonyl Sulfide (OCS) in the Upper Troposphere and Stratosphere

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. Outline.

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Global Distributions of Carbonyl Sulfide (OCS) in the Upper Troposphere and Stratosphere

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  1. 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

  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 resn. FTIR) • ACE vs. MkIV data (Balloon-borne high resn. FTIR) • Global Distributions • Global Maps • Zonal means & latitudinal profiles • Estimate of OCS stratospheric Lifetime • Summary Michael Barkley, University of Edinburgh

  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 CO2 • Can OCS constrain GPP/biospheric fluxes of C? • Uncertainty in budget OCS seasonal cycle similar to CO2 Michael Barkley, University of Edinburgh

  4. OCS Global Budget Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks Atmospheric Losses: OH: -94 (12) O: -11 (5) hv: -16 (5) --------- Tot: -121 (14) ~9% OCS(~0.3Tg) OCS SO2 Aerosols Stratosphere 0.31Tg 0.34Tg Chin & Davis, JGR, 1995 Troposphere Flux (error) [Gg S] 41 (154) SO2 OCS(~2.5Tg) OCS 84 (54) 116 (58) 154 (37) 70 (50) -130 (56) -238 (30) 64 (32) CS2 DMS CS2 Michael Barkley, University of Edinburgh

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

  6. ACE OCS retrievals Fitting windows • Use improved v2.2 ‘research products’ • More micro-windows & higher altitudes • Uses HITRAN 2004 • 8 interfering species fitted simultaneously: • OCS • Isotopologue 2 • O3 • Isotopolgues 1 & 3 • CO2 • Isotopolgues 1,2,3 & 4 • H2O Low z = 8 – 2 x [sin(lat)]2 Pole to Equator Michael Barkley, University of Edinburgh

  7. ACE OCS No data below ~6 km or above ~31 km Total # occultations = 10251 Few measurements > 600 pptv Michael Barkley, University of Edinburgh

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

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

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

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

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

  13. ACE OCS Global Distributions (2004-2006) Michael Barkley, University of Edinburgh

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

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

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

  17. Seasonal Maps at 9.5 km Michael Barkley, University of Edinburgh

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

  19. Mean Latitudinal Profiles Michael Barkley, University of Edinburgh

  20. Mean Latitudinal Profiles Michael Barkley, University of Edinburgh

  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] T1 = T2 x (dΩ2/dΩ1) x (Ω1/Ω2) • Use coincidental ACE measurements of CFC-11 and CFC-12 + & CFC lifetimes & tropospheric VMRs from the WMO 2006 report: • CFC-11 (CFCl3) • Ω = 254 pptv, T=45±10 yrs • CFC-12 (CF2Cl2) • 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 Edinburgh

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

  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 strats sink = tropospheric flux • Tropospheric sulfur flux (in the form of OCS) required to sustainthestratospheric 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 Edinburgh

  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 strats 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 Edinburgh

  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) Michael Barkley, University of Edinburgh

  26. End

  27. ACE vs. Aircraft Aircraft data courtesy of Stephen Montzka GMD, NOAA • GMD NOAA aircraft flights (grey lines) constrained to region: • 40 - 48 °N • 89 - 104.3 °W • ACE sampled over: • 25 - 55 °N • 70- 125 °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! Michael Barkley, University of Edinburgh

  28. Summary of MkIV and ATMOS instruments • MkIV • Balloon-borne high resolution FTIR • Covers 650-5650 cm-1 spectral region at 0.01 cm-1 resolution • Solar Occultation • ATMOS • Atmospheric Trace Molecule Spectroscopy experiment • Balloon-borne high resolution FTIR • Covers 600-4800 cm-1 spectral region at 0.01 cm-1 resolution • Solar Occultation Michael Barkley, University of Edinburgh

  29. Finely balancing the OCS global budget Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks “…within the large associated range of uncertainties..” • Total sources = 592 (166-1071)†[210-1049]* • Total sinks = 489 (380-597) †[902-1827]* • † = Suntharalingham et al, JGR (sub), 2007 (GEOS-Chem) • * =Montzka et al, JGR, 2007 (Observations + Kettle fluxes) Michael Barkley, University of Edinburgh

  30. Past Variability Drop not understood Sulfur emissions? Deforestation? Viscose rayon production of CS2? Little Ice Age 1550-1850 AD Montzka et al., JGR, 2004 Michael Barkley, University of Edinburgh

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