Article

Applied Physics B

, Volume 90, Issue 2, pp 301-309

First online:

New method for isotopic ratio measurements of atmospheric carbon dioxide using a 4.3 μm pulsed quantum cascade laser

  • D.D. NelsonAffiliated withAerodyne Research, Inc. Email author 
  • , J.B. McManusAffiliated withAerodyne Research, Inc.
  • , S.C. HerndonAffiliated withAerodyne Research, Inc.
  • , M.S. ZahniserAffiliated withAerodyne Research, Inc.
  • , B. TuzsonAffiliated withLaboratory for Air Pollution and Environmental Technology, EMPA, Swiss Federal Laboratories for Materials Testing and Research
  • , L. EmmeneggerAffiliated withLaboratory for Air Pollution and Environmental Technology, EMPA, Swiss Federal Laboratories for Materials Testing and Research

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

We present a new approach to the measurement of stable isotopic ratios of carbon dioxide using a near-room-temperature pulsed quantum cascade laser and a spectral ratio method based upon dual multiple pass absorption cells. The spectral ratio method improves precision and accuracy by reducing sensitivity to variations in the laser tuning rate, power and line width. The laser is scanned across three spectral lines (near 2310 cm-1) quantifying three CO2 isotopologues: 12C16O2, 13C16O2 and 12C16O18O. Isotopic ratios are determined simultaneously with a precision of 0.2δ for each ratio with a one-second measurement. Signal averaging for 400 s improves the precision to better than 0.03δ for both isotopic ratios (13 R and 18 R). Long-term accuracy of 0.2 to 0.3δ is demonstrated with replicate measurements of the same sample over a one-month period. The fast time response of this instrument is suitable for eddy flux measurements.