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data_processing

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Data processing

CO2 data reduction

(1) Compute the isotopologue composition of your reference gas

…using the following parameters:

  • δ13CRef: the nominal carbon isotope composition of your reference gas vs VPDB
  • δ18ORef: the nominal oxygen isotope composition of your reference gas vs VSMOW
  • λ = 0.5164, the terrestrial mass-dependent fractionation parameter between 17O and 18O [missing reference]
  • R13-VPDB = 0.0112372, the abundance ratio of 13C/12C for VPDB [missing reference]
  • R17-VSMOW = 0.0003799, the abundance ratio of 17O/16O for VSMOW [missing reference]
  • R18-VSMOW = 0.0020052, the abundance ratio of 18O/16O for VSMOW [missing reference]

(1.a) Compute abundance ratios of 13C/12C, 17O/16O and 18O/16O

  • R13-Ref = R13-VPDB × (1 + δ13CRef/1000)
  • R18-Ref = R18-VSMOW × (1 + δ18ORef/1000)
  • R17-Ref = R17-VSMOW × (R18-Ref / R18-VSMOW)λ

(1.b) Compute abundances of 12C, 13C, 16O, 17O and 18O

  • C12-Ref = 1 / (1 + R13-Ref)
  • C13-Ref = R13-Ref / (1 + R13-Ref)
  • C16-Ref = 1 / (1 + R17-Ref + R18-Ref)
  • C17-Ref = R17-Ref / (1 + R17-Ref + R18-Ref)
  • C18-Ref = R18-Ref / (1 + R17-Ref + R18-Ref)

(1.c) Compute abundances of isotopologues with masses 44 to 49

…by making the assumption that your reference gas is stochastic (this is usually not true, but we correct for that later in the process).

  • Mass 44:
    • C12-16-16-Ref = C12-Ref × C16-Ref × C16-Ref
  • Mass 45:
    • C13-16-16-Ref = C13-Ref × C16-Ref × C16-Ref
    • C12-17-16-Ref = C12-Ref × C17-Ref × C16-Ref × 2
  • Mass 46:
    • C12-18-16-Ref = C12-Ref × C18-Ref × C16-Ref × 2
    • C13-17-16-Ref = C13-Ref × C17-Ref × C16-Ref × 2
    • C12-17-17-Ref = C12-Ref × C17-Ref × C17-Ref
  • Mass 47:
    • C13-18-16-Ref = C13-Ref × C18-Ref × C16-Ref × 2
    • C13-17-17-Ref = C13-Ref × C17-Ref × C17-Ref
    • C12-18-17-Ref = C12-Ref × C18-Ref × C17-Ref × 2
  • Mass 48:
    • C13-18-17-Ref = C13-Ref × C18-Ref × C17-Ref × 2
    • C12-18-18-Ref = C12-Ref × C18-Ref × C18-Ref
  • Mass 49:
    • C13-18-18-Ref = C13-Ref × C18-Ref × C18-Ref

(1.d) Compute binned abundances of isotopologues grouped by mass

  • C44-Ref = C12-16-16-Ref
  • C45-Ref = C13-16-16-Ref + C12-17-16-Ref
  • C46-Ref = C12-18-16-Ref + C13-17-16-Ref + C12-17-17-Ref
  • C47-Ref = C13-18-16-Ref + C13-17-17-Ref + C12-18-17-Ref
  • C48-Ref = C13-18-17-Ref + C12-18-18-Ref
  • C49-Ref = C13-18-18-Ref

(2) Compute the composition of your sample gas

(2.a) Measure the abundance ratios of your sample gas for masses 45 to 49

…based on voltage measurements from your dual-inlet spectrometer:

  • V44-Ref … V49-Ref for your reference gas
  • V44-Sample … V49-Sample for your sample gas

Ideally, these voltages reflect abundance ratios, so that:

  • R45-Sample = R45-Ref × V45-Sample / V44-Sample × V44-Ref / V45-Ref
  • R46-Sample = R46-Ref × V46-Sample / V44-Sample × V44-Ref / V46-Ref
  • R47-Sample = R47-Ref × V47-Sample / V44-Sample × V44-Ref / V47-Ref
  • R48-Sample = R48-Ref × V48-Sample / V44-Sample × V44-Ref / V48-Ref
  • R49-Sample = R49-Ref × V49-Sample / V44-Sample × V44-Ref / V49-Ref

And, using the conventional δ notation (relative to your reference gas):

  • δ45 = 1000 × (1 - R45-Sample/R45-Ref) = 1000 × (1 - V45-Sample / V44-Sample × V44-Ref / V45-Ref)
  • δ46 = 1000 × (1 - R46-Sample/R46-Ref) = 1000 × (1 - V46-Sample / V44-Sample × V44-Ref / V46-Ref)
  • δ47 = 1000 × (1 - R47-Sample/R47-Ref) = 1000 × (1 - V47-Sample / V44-Sample × V44-Ref / V47-Ref)
  • δ48 = 1000 × (1 - R48-Sample/R48-Ref) = 1000 × (1 - V48-Sample / V44-Sample × V44-Ref / V48-Ref)
  • δ49 = 1000 × (1 - R49-Sample/R49-Ref) = 1000 × (1 - V49-Sample / V44-Sample × V44-Ref / V49-Ref)

(2.b) Compute the bulk composition of your sample gas

(to be continued soon)

data_processing.1273073268.txt.gz · Last modified: 2012/04/04 09:08 (external edit)