Simulative Study on the Sources and Sinks of OCS under lightning

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Simulative Study on the Sources and Sinks of OCS
under lightning

• Jie Zhu

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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

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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

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About CS2

• CS2 oxidation is a very important source of OCS
• CS2O ?OCSS
• CS2OH ?OCSHS

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SO2 and sulfur cycle in the atmosphere
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Global Sulfur Emissions
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Why study on lightning?

• Under UV light CS2OH
• Lightning flashes are a very normal nature
  phenomena, they happens 100 times/sec in the earth

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Global lighting flashes distribution
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What is lightning?
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Spark discharge?
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?Franklins 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
Franklins Kite Experiment
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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

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The system studied and products analysis

• CS2air system (pCS21.33?103Pa, pair1.01
  ?105Pa)
• Products CO2, CO,OCS, N2O
• SO2CH4O2 system(pSO21.33?103Pa,
  pCH41.33?103Pa, pO2 1.01 ?105Pa)
• Products CO, OCS
• OCS system
• OCSO2(pOCS1.33?103Pa, pO2 1.01 ?105Pa)
• Products CO2, CO, SO3
• OCSdry air(pOCS1.33?103Pa, pair 1.01 ?105Pa)
• Products CO2, CO, SO3, N2O
• OCS water saturated air(pOCS1.33?103Pa, pair
  1.01 ?105Pa)
• Products CO2, CO, H2SO4, N2O

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Reaction mechanism supposed

• eO2 ?eOO
• e H2O ?eOHH

• ? CS2air system
• eCS2?eCSS
• O CS2 ?OCSS
• OH CS2 ?OCSS
• CSO2?OCSSO

OH, O and e particles are produced in a
lightning flash
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Reaction mechanism supposed

• SO2CH4O2 system
• eSO2?eSOO
• eCH4?eCH3(CH2?CH)H
• CH2SO2?OCSH2O
• CHSO ?OCSH

• OCS system
• eOCS?eCOS
• OOCS?SOCO
• OHOCS?CO2SH
• SOO2 ?SO3
• SO3H2O ?HSO4

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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 ?OHgtgt?Ogtgt?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
  ?OCSS, k1,
  OHOCS?CO2SH, k2

OH radicals are the most important species!!!!
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Practical Calculations

• In a lightning flash,
• dOCS/dtk1CS2OH-k2OCSOH
• Using the data of the rate constant, k11.85 ?10
  13cm3s-1, k2 5.7 ?10 14cm3s-1,and the global
  mean OCS and CS2 concentration to calculate, we
  get
• dOCS/dt lt 0
• That means lightning flashes destroy OCS in
  global scale.

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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.,2000,34761-769
• 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 299430K,Chem. Phys.
  Lett., 1978,5414-18
• 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

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Thank You!