Development of airborne instrument for CO measurement

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An airborne instrument for fast-response, high-precision measurement of tropospheric carbon monoxide (CO) was developed using a vacuum ultraviolet (VUV) resonance fluorescence technique. The excitation radiation is obtained by a DC discharge CO resonance lamp combined with an optical filter for the CO 4^<th> positive band emission around 150nm. The optical filter consists of a VUV monochromator and a crystalline quartz window (<147nm cutoff). The crystalline quartz window ensures sharp discrimination against wavelengths below 135.7nm, which yields a positive interference from water vapor. Laboratory tests showed that the optical system achieves a precision of 1.1 parts per billion by volume(ppbv) at a CO concentration of 100ppbv for a 1-seconds intergration period, and flow system provides a response time(1/e time constant) of about 2 seconds. The aircraft measurement campaign Biomass Burning and Lightning Experiment-phase B (BIBLE-B ) took place between August and September 1999 over Australia. The flight data obtained during this campaign are used to demonstrate the high precision and fast response of the instrument. An intercomarison of the VUV CO measurement and a gas chromatographic CO measurement was conducted during BIBLE-B. Overall, these two independent measurements showed good agreement, within the experimental uncertainties.