1. FACTORS GOVERNING THE SEASONAL VARIABILITY OF ATMOSPHERIC CARBONYL SULFIDE Parv Suntharalingam Harvard/Univ. of East Anglia A.J. Kettle, S. Montzka, D. J. Jacob GEOS-Chem Meeting April 12 th, 2007

2. Carbonyl Sulfide (COS) Uptake by Leaf During Photosynthesis Can Carbonyl Sulfide help in Constraining Estimates of Global Primary Production ? COS CO 2 COS and CO 2 are taken up through leaf stomata during photosynthesis CO 2 COS GPP : Gross flux of CO 2 converted to organic matter during photosynthesis

3. SEASONAL CYCLES OF COS and CO 2 COS measurements : S. Montzka (NOAA-GMD) CO 2 SH COS J F M A M J J A S O N D Seasonal cycles of COS and CO 2 are correlated, especially at forested sites. CAN COS MEASUREMENTS CONSTRAIN BIOSPHERIC CO 2 UPTAKE ? Significant uncertainties remain on aspects of COS budget

4. SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE COS Mean atmospheric conc. ~ 500 ppt

5. SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE ANTHROPOGENIC OCEAN CS 2 DMS COS Oxidation

6. SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE SOILS PLANTS ANTHROPOGENIC OCEAN CS 2 DMS COS Tropospheric Oxidation, Stratospheric Photolysis Oxidation

7. SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE SOILS PLANTS ANTHROPOGENIC OCEAN CS 2 DMS COS Tropospheric Oxidation, Stratospheric Photolysis Oxidation Biomass Burning ?? Uncertainty remains on source/sink fluxes

8. ATMOSPHERIC COS BUDGET Kettle et al. [2002] : Gridded Fields Not included here Biomass Burning : 35 Tg S (8%) Stratospheric Photolysis : 16 Tg (3.5%) Minor sources : < 3% ANNUALLY BALANCED BUDGET Total sources/sinks : 460 Gg S/year -238-130-92 -180280 Also based on : Chin and Davis, 1993; Watts, 2000

9. OUTLINE 1.Model atmospheric COS with recent best estimates of seasonal sources and sinks [Kettle et al. 2002] 2.Evaluate against measurements from global observation network [Montzka et al. 2006] 3.Which processes govern observed seasonal variability ? Can we improve estimates of prior COS fluxes? AIM : Improved constraints on factors governing COS seasonal variability

10. COS SURFACE OBSERVATION NETWORK : NOAA-GMD F lask measurements since 2000 [Montzka et al. 2006] Barrow (BRW) Mauna Loa (MLO) South Pole (SPO) cgo mhd alt brw kum mlo smo spo nwr hfm lef

11. GEOS-Chem COS SIMULATION INPUT FLUX DISTRIBUTIONS [Kettle et al. 2002] SOURCES Ocean (Direct; CS 2 and DMS oxidation to COS) Anthropogenic (Direct and CS 2 oxidation to COS) SINKS Terrestrial plant uptake Soil uptake COS oxidation by OH (tropospheric) To be Implemented Biomass burning Stratospheric photolysis GEOS-Chem Version 7-03-06 Resolution : 2x2.5; 30 vertical levels Meteorology Year : 2001

12. COS SINK DISTRIBUTIONS [Kettle et al. 2002] Plant Uptake (JAN) Plant Uptake (JUL) Soil Uptake (JAN) Soil Uptake (JUL) Plant fluxes derived from NPP and NDVI fields Soil uptake based on soil moisture and temperature. (Only 1 soil type) pmol/m 2 /sec

13. Anthropogenic (JAN) Anthropogenic (JUL) Ocean (JAN) Ocean (JUL) Anthropogenic COS fluxes distributed according to SO 2 emissions (GEIA 1985) Ocean fluxes based on ocean photochemical model and DMS distributions COS SOURCE DISTRIBUTIONS [Kettle et al. 2002] pmol/m 2 /sec

14. SEASONAL VARIABLITY OF COS FLUXES Flux Distributions : Kettle et al [2002] AGGREGATED FLUXES N Hemisphere variability driven by plant uptake and ocean fluxes S Hemisphere variability driven by ocean fluxes OCEAN TOTAL SURFACE COS FLUX PLANT SOILS ANTH.OCEAN Northern Hemisphere Southern Hemisphere Gg S per month

15. SEASONAL ANOMALIES AT MEASUREMENT SITES Data : S. Montzka (NOAA-GMD ) South Pole Cape Grim, Tasmania Barrow, AlaskaPark Falls, Wisconsin Seasonal cycle has similar phase at Southern Hemisphere and Northern Hemisphere sites Northern Hemisphere sites show larger seasonal amplitude Data for years 2001-2005

16. SEASONAL CYCLE AT REMOTE/OCEAN SITES Observations and Model : Seasonal Anomalies Good agreement at Southern Hemisphere remote/ocean sites X Observations Model

17. Good agreement at Southern Hemisphere remote/ocean sites Observed seasonality not well reproduced as move northwards X Observations Model SEASONAL CYCLE AT REMOTE/OCEAN SITES Observations and Model : Seasonal Anomalies

18. SEASONAL CYCLE AT TERRESTRIAL STATIONS Observations and Model : Seasonal Anomalies Observed seasonal cycle not well simulated at Northern Hemisphere terrestrial sites X Observations Model

19. GLOBAL PLANT UPTAKE OF COS SUMMARY OF ESTIMATES : (Table 4 : Sandoval-Soto et al. 2005 ) Units : Tg COS/year Brown and Bell (1986)2-5 Goldan et al. 19880.2-0.6 Kesselmeier and Merk (1993)0.93 + 0.07 Chin and Davis (1993)0.16-0.91 Watts (2000)0.56 + 0.1 Xu et al. (2002)2.3 + 0.5 Kettle et al. (2002)0.39 – 0.5 Sandoval-Soto et al. (2005)1.37-2.81 Kettle et al. [2002] NPP-based estimate is lower than recent estimates

20. SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3) X Observations Original Model Model: Increased plant uptake ORIG MODEL INCREASED UPTAKE MODEL Increased COS uptake by plants better matches observed seasonality

21. SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3) X Observations Original Model Increased plant uptake BUT Now need an additional source (for balanced annual budget)

22. SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3) X Observations Original Model Increased plant uptake BUT Now need an additional source (for balanced annual budget) Phase problems remain

23. SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3) X Observations Original Model Increased plant uptake BUT Now need an additional source (for balanced budget) Phase problems remain Missing source flux ?

24. SUMMARY Add source and sink for biomass burning and stratospheric photolysis Update anthropogenic COS emissions based on latest SO 2 inventories. Inverse model analysis of COS measurements to improve source/sink flux estimates Primary influences on COS seasonal cycle : Ocean fluxes in Southern Hemisphere; Plant uptake and ocean fluxes in Northern Hemisphere. Increasing plant uptake of COS by a factor of 3 (to 0.7 Tg S/year) improves model representation of seasonal cycle at terrestrial sites But, annual COS budget no longer in balance – missing source ? ONGOING/PLANNED WORK