Abstract
Abstract. Despite the importance of carbon monoxide (CO) for the overall oxidative capacity of the atmosphere, there is still considerable uncertainty in ambient measurements of CO. To address this issue, an inter-comparison between four different measurement techniques was made over a period of two months at the high-alpine site Jungfraujoch (JFJ), Switzerland. The measurement techniques were Non-dispersive Infrared Absorption (NDIR), Vacuum UV Resonance Fluorescence (VURF), gas chromatographic separation with a mercuric oxide reduction detector (GC/HgO), and gas chromatographic separation followed by reduction on a nickel catalyst and analysis by a flame ionization detector (GC/FID). The agreement among all techniques was better than 2% for one-hourly averages, which confirmed the suitability of the NDIR method for CO measurements even at remote sites. The inter-comparison added to the validation of the 12-year record (1996–2007) of continuous CO measurements at JFJ. To date this is one of the longest time series of continuous CO measurements in the free troposphere over Central Europe. This data record was further investigated with a focus on trend analysis. A significant negative trend was observed at JFJ showing a decrease of 21.4±0.3% over the investigated period, or an average annual decrease of 1.78%/yr (2.65±0.04 ppb/yr). These results were compared with emission inventory data reported to the Long-range Transboundary Air Pollution (LRTAP) Convention. It could be shown that long range transport significantly influences the CO levels observed at JFJ, with air masses of non-European origin contributing at least one third of the observed mole fractions.
Highlights
Carbon monoxide (CO) plays an important role in atmospheric chemistry
This study presents results from an inter-comparison of several currently used in-situ techniques (NDIR, Vacuum UV Resonance Fluorescence (VURF), gas chromatographic (GC)/HgO, GC/flame ionization detector (FID)) for the measurement of atmospheric CO, which are normally used in international programs and networks
Data availability based on one-hourly averages was 96.7% (NDIR), 86.4% (VURF), 86.7% (GC/FID), and 98.9% (GC/HgO)
Summary
Carbon monoxide (CO) plays an important role in atmospheric chemistry. Reactions involving CO provide the dominant sink for the hydroxyl radical (Logan et al, 1981), and together with nitrogen oxides, the level of CO largely controls the overall oxidative capacity of the atmosphere. CO plays an important role as a precursor of tropospheric ozone (Levy et al, 1997). CO has a relatively long atmospheric lifetime, ranging from 10 days in summer over continental regions to more than a year over polar regions in winter (Holloway et al, 2000b). This lifetime is long enough to make use of CO as a sound tracer for anthropogenic pollution
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