Differential Optical Absorption Spectroscopy (DOAS)

  • Use differences of intensities, rather than absolute intensities
  • Simultaneously record many (typ. several 100) wavelength intervals (measurement of numerous gases)
  • High pass-filtering of spectra remove continuum
  • Fit reference spectra make use of all spectral information
  • High sensitivity, selectivity
  • Inherently calibrated
  • Warning against unknown absorbers

Differential reduction in intensity D’ due to differential absorption cross-section σ‘ of an atmospheric trace gas.

Cross sections of selected atmospheric absorbers

Lambert-Beers Law:

I = I0*exp(-σ*c*L)

  • σ: cross section
  • c: concentration of absorber
  • L: light path through absorber