Simulative Study on the Sources and Sinks of OCS under lightning

1. Simulative Study on the Sources and Sinks of OCS under lightning Jie Zhu

2. Content • The importance of study on OCS, CS2, SO2/CH4 • Why study on lightning • The similarity of natural lightning and spark discharge • Some experimental results • Mechanism of the reactions • Global calculation and discussion of practical analysis

3. About OCS • The most abundant sulfur gas in the atmosphere • Long-lived in the atmosphere (about 4 years) • Contribute to form SO2 and SO3, and sulfate aerosol

4. About CS2 CS2 oxidation is a very important source of OCS CS2+O OCS+S CS2+OH OCS+HS

5. SO2 and sulfur cycle in the atmosphere

6. Global Sulfur Emissions

7. Why study on lightning? Under UV light : CS2+OH Lightning flashes are a very normal nature phenomena, they happens 100 times/sec in the earth

8. Global lighting flashes distribution

9. What is lightning?

10. Spark discharge?

11. Franklin’s Kite Experiment Franklin’s famous kite experiment testifies lightning and spark discharge are actually the same thing Conclusion: Using spark discharge to simulate the lighting and to study the reactions of OCS under lightning is reasonable

12. An easily operated experiment • Gases studied are filled in the cell • Spark discharge in the cell • The reaction products are analyzed by FT-IR spectra technique

13. The system studied and products analysis • CS2+air system (pCS2=1.33103Pa, pair=1.01 105Pa) Products: CO2, CO,OCS, N2O • SO2+CH4+O2 system(pSO2=1.33103Pa, pCH4=1.33103Pa, pO2=1.01 105Pa) Products: CO, OCS • OCS system • OCS+O2(pOCS=1.33103Pa, pO2=1.01 105Pa) Products: CO2, CO, SO3 • OCS+dry air(pOCS=1.33103Pa, pair=1.01 105Pa) Products: CO2, CO, SO3, N2O • OCS+ water saturated air(pOCS=1.33103Pa, pair=1.01 105Pa) Products: CO2, CO, H2SO4, N2O

14. Reaction mechanism supposed e*+O2e+O+O e*+H2O e+OH+H •  CS2+air system: • e*+CS2e+CS+S • O+ CS2 OCS+S • OH+ CS2 OCS+S • CS+O2OCS+SO OH, O and e* particles are produced in a lightning flash

15. Reaction mechanism supposed • SO2+CH4+O2 system e*+SO2e+SO+O e*+CH4e+CH3(CH2、CH)+H CH2+SO2OCS+H2O CH+SOOCS+H • OCSsystem • e*+OCSe+CO+S • O+OCSSO+CO • OH+OCSCO2+SH • SO+O2 SO3 • SO3+H2OHSO4

16. Practical Calculations Main points: • The fraction of reaction of SO2 with CH4 to form OCS is relatively small because of very small reaction rate constant. (This will be discussed in the paper turned up). • The lightning flash produces reactive species as e*, O and OH. As OH>>O>>e*, we consider OH radicals be the main species to react with OCS, CS2 et al. • So the key reactions contributing to OCS changing in a lightning flash are: OH+ CS2 OCS+S, k1, OH+OCSCO2+SH, k2 OH radicals are the most important species!!!!

17. Practical Calculations • In a lightning flash, d[OCS]/dt=k1[CS2][OH]-k2[OCS][OH] • Using the data of the rate constant, k1=1.85 10 –13cm3s-1, k2= 5.7 10 –14cm3s-1,and the global mean OCS and CS2 concentration to calculate, we get: d[OCS]/dt < 0 That means lightning flashes destroy OCS in global scale.

18. References: • Egorova T, Zubov V, Jagovkina S, et al. Lightning production of Nox and Ozone. Phys. Chem.Earth.,1999,24(5):473-479 • Simon F, The mass budgets of carbonyl sulfide,dimethyl sulfide, carbon disulfide and hydrogen sulfide, Atmos. Environ.,2000，34：761-769 • William P, Julian H, The photooxidation of carbon disulfide, The Journal of Physical Chemistry.,1971,75(7):854-860 • Chin M, Davis DD. Global sources and sinks of OCS and CS2, and their distribution. Global Biogeochemical Cycles, 1993,&:321-337 • Atkinson R, et al. Rate constants for the reaction of OH radicals with OCS, CS2,and CH3SCH3 over the temperature range 299~430K，Chem. Phys. Lett., 1978,54:14-18 • Kuhn U, et at. Carbonyl sulfide exchange on an ecosystem scale: soil represents a dominant sink for atmospheric COS. Atmos. Environ.,1999,33: 995-1008

19. Thank You!