title: 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.
authors.affiliation: Los Gatos Research, 67 East Evelyn Avenue, Suite 3, Mountain View, California, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Provencal
authors.forename: Manish
authors.initials: M
authors.lastname: Gupta
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Owano
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Baer
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Ricci
authors.forename: Anthony
authors.initials: A
authors.lastname: O'Keefe
authors.forename: James R
authors.initials: JR
authors.lastname: Podolske