Cavity-enhanced quantum-cascade laser-based instrument for carbon monoxide measurements

Abstract

An autonomous instrument based on off-axis integrated cavity output spectroscopy has been developed and successfully deployed for measurements of carbon monoxide in the troposphere and tropopause onboard a NASA DC-8 aircraft. The instrument (Carbon Monoxide Gas Analyzer) consists of a measurement cell comprised of two high-reflectivity mirrors, a continuous-wave quantum-cascade laser, gas sampling system, control and data-acquisition electronics, and data-analysis software. CO measurements were determined from high-resolution CO absorption line shapes obtained by tuning the laser wavelength over the R(7) transition of the fundamental vibration band near 2172.8 cm(-1). The instrument reports CO mixing ratio (mole fraction) at a 1-Hz rate based on measured absorption, gas temperature, and pressure using Beer's Law. During several flights in May-June 2004 and January 2005 that reached altitudes of 41,000 ft (12.5 km), the instrument recorded CO values with a precision of 0.2 ppbv (1-s averaging time) and an accuracy limited by the reference CO gas cylinder (uncertainty < 1.0%). Despite moderate turbulence and measurements of particulate-laden airflows, the instrument operated consistently and did not require any maintenance, mirror cleaning, or optical realignment during the flights.

Evaluation of new laser spectrometer techniques for in-situ carbon monoxide measurements

“…However, for long-term monitoring programmes, such high temporal resolution is not required, and appropriate averaging intervals will lead to compatible data with all techniques. The precision of the tested ICOS-QCL analyser was slightly better (standard deviation of 0.09 ppb over one hour at 271.1 ppb CO) compared to data acquired with a prototype instrument (0.2 ppb over 10 min at 32.7 ppb) (Provencal et al, 2005). A further aspect that potentially compromises the instrument performance is instrument drift, i.e.…”

IASI carbon monoxide validation over the Arctic during POLARCAT spring and summer campaigns

“…On board the DC-8 many measurements were performed including aerosol properties, black carbon (BC), SO 2 , peroxy acetic acid, acetaldehyde, acetone, acetonitrile, benzene, isoprene, methanol, toluene, Hg, CO, O 3 , CH 2 O, H 2 O 2 , H 2 O, HO 2 , HCN, OH, HNO 3 , PAN, NO, NO 2 , NO y , and H 2 SO 4 . Measurements of CO on the NASA DC-8 as part of ARCTAS were made using a tunable diode laser absorption (TDLAS) (Sachse et al, 1987) whilst measurements on the P-3B were made using the COBALT instrument, which employs off-axis Integrated Cavity Output Spectroscopy (oa-ICOS) (Provencal et al, 2005).…”

Carbon monoxide measurements onboard the CARIBIC passenger aircraft using UV resonance fluorescence

“…TDLAS in the mid-infrared (Sachse et al, 1987, Wienhold et al, 1998, do show a comparable performance, but are much more complex and require skilled personnel for its use. Recently, a CRDS instrument has been reported to have achieved a precision of 0.2 ppbv with 1 s time resolution onboard aircraft, accompanied by nearly care-free operation (Provencal et al, 2005). We are not aware of any long-term experience with this instrument.…”

“…These four techniques were inter-compared at the high-altitude Jungfraujoch observatory (Switzerland) and found to agree within 2 % for one-hourly averages. Increasingly used are commercial instruments based on wavelength-scanned cavity ring-down spectroscopy (WS CRDS, Provencal et al, 2005;WMO, 2010). The original tunable diode laser absorption spectroscopy (TDLAS) was pioneered by several groups for research aircraft applications (Sachse et al, 1987;Wienhold et al, 1998).…”