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Simulative Study on the Sources and Sinks of OCS under lightning

Simulative Study on the Sources and Sinks of OCS under lightning. Jie Zhu. Content. The importance of study on OCS, CS 2 , SO 2 /CH 4 Why study on lightning The similarity of natural lightning and spark discharge Some experimental results Mechanism of the reactions

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Simulative Study on the Sources and Sinks of OCS under lightning

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  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!

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