2.4. Carbon Monoxide
2.4.1. In Situ Carbon Monoxide Measurements
Instruments based upon gas chromatography and mercuric oxide reduction and UV absorption (Reduced Gas Analyzer (RGA) from Trace Analytical Inc, Menlo Park, California) were installed at BRW and MLO in 1991 and 1992, respectively. The analytical techniques have been described previously [Bakwin et al., 1994]. In brief, the analysis of samples using a RGA were compared to standards bracketing the range of mole fractions found at the site, and standards were referenced to the CMDL calibration scale. A piecewise linear calibration procedure using three standards was used to account for nonlinear instrument response. Measurements at BRW continued with only minor problems during 1996-1997. The BRW time series shows a strong seasonal cycle with an amplitude of ~100 ppb (10-9 mol mol-1) (Figure 2.16). The large seasonal difference found at BRW is a common feature of CO at sites throughout the Arctic (Figure 2.17a).
Fig. 2.16. Carbon monoxide time series determined at BRW. Solid lines are hourly means of four to five analyses per hour. Circles are mole fractions determined from grab samples.
Fig. 2.17. (a) Overlay of time series determined from grab samples from Alert, Canada, Mould Bay, Canada, Point Barrow, Alaska, and Iceland. (b) Same for sites located in the high southern hemisphere.
The RGA at MLO continued to be plagued by problems. In late 1996 chromatographic parameters of the instrument became erratic, and during the next few months various parts were replaced and columns reconditioned. After no improvement, the instrument was returned to Boulder. This instrument continues to experience reoccurring problems with its hardware and has not yet been returned to the observatory.