. Since 1992 semi-continuous in-situ observations of greenhouse gas concentrations have been performed at the tall tower of Cabauw (4.927° E, 51.971° N, −0.7 m a.s.l.). Through 1992 up to now, the measurement system has been gradually extended and improved in precision, starting with CO2 and CH4 concentrations from 200 m a.g.l. in 1992 to vertical gradients at 4 levels of the gases CO2, CH4, SF6, N2O, H2, CO and gradients at 2 levels for 222Rn. In this paper the measurement systems and measurement results are described for the main greenhouse gases and CO, for the whole period. The automatic measurement system now provides half-hourly concentration gradients with a precision better than or close to the WMO recommendations. The observations at Cabauw show a complex pattern caused by the influence of sources and sinks from a large area around the tower with significant contributions of sources and sinks at distances up to 500–700 km. The concentration footprint area of Cabauw is one the most intensive and complex source areas of greenhouse gases in the world. Despite this, annual mean trends for the most important greenhouse gases, compatible with the values derived using the global network, can be reproduced from the measured concentrations at Cabauw over the entire measurement period, with a measured increase in the period 2000–2009 for CO2 of 1.90 ± 0.1 ppm yr−1, for CH4 of 4.4 ± 0.6 ppb yr−1, for N2O of 0.86 ± 0.04 ppb yr−1, and for SF6 of 0.27 ± 0.01 ppt yr−1; for CO no significant trend could be detected. The influences of strong local sources and sinks are reflected in the amplitude of the mean seasonal cycles observed at Cabauw, that are larger than the mean Northern Hemisphere average; Cabauw mean seasonal amplitude for CO2 is 25–30 ppm (higher value for lower sampling levels). The observed CH4 seasonal amplitude is 50–110 ppb. All gases except N2O show highest concentrations in winter and lower concentrations in summer, N2O observations show two additional concentration maxima in early summer and in autumn. Seasonal cycles of the day-time mean concentrations show that surface concentrations or high elevation concentrations alone do not give a representative value for the boundary layer concentrations, especially in winter time, but that the vertical profile data along the mast can be used to construct a useful boundary layer mean value. The variability at Cabauw in the atmospheric concentrations of CO2 on time scales of minutes to hours is several ppm and is much larger than the precision of the measurements (0.1 ppm). The diurnal and synoptical variability of the concentrations at Cabauw carry information on the sources and sinks in the footprint area of the mast, that will be useful in combination with inverse atmospheric transport model to verify emission estimates and improve ecosystem models. For this purpose a network of tall tower stations like Cabauw forms a very useful addition to the existing global observing network for greenhouse gases.

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Greenhouse gas observations from Cabauw Tall Tower (1992–2010)

Carbon monoxide (CO), carbon dioxide (CO2), and radiocarbon (14CO2) measurements have been made in Heidelberg from 2001 to 2004 in order to determine the regional fossil fuel CO2 component and to investigate the application of CO as a quantitative tracer for fossil fuel CO2 (CO2(foss)). The observations were compared with model estimates simulated with the regional transport model REMO at 0.5° × 0.5° resolution in Europe for 2002. These estimates are based on two available emissions inventories for CO and CO2(foss) and simplified atmospheric chemistry of CO. Both emissions inventories appear to overestimate fossil fuel emissions in the Heidelberg catchment area, in particular in summer and autumn by up to a factor of 2. Nevertheless, during meteorological conditions with high local source influence the CO/CO2(foss) emission ratios compared well with the observed atmospheric CO/CO2(foss) ratios. For a larger catchment area of several 100 km the observed CO/CO2(foss) ratio compared within better than 25% with the ratios derived from model simulations that take the transport from the sites of emission to the measurement station into account. Non-fossil-fuel CO emissions, production by volatile organic compounds, and oxidation, as well as soil uptake, turned out to add significant uncertainty to the application of CO as a quantitative fossil fuel CO2 surrogate tracer, so that 14CO2 measurements seem to be indispensable for reliable estimates of fossil fuel CO2 over the European continent. (Less)

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JD006966

Carbon monoxide : a quantitative tracer for fossil fuel CO2?

A 7-year-long data set of integrated high-precision 14 CO 2 observations combined with occasional hourly 14 CO 2 flask data from the Heidelberg sampling site is presented. Heidelberg is located in the highly populated and industrialized upper Rhine valley in southwestern Germany. The 14 CO 2 data are used in combination with hourly carbon monoxide (CO) observations to estimate regional hourly fossil fuel CO 2 (ΔFFCO 2 ) mixing ratios. We investigate three different 14 C calibration schemes to calculate ΔFFCO 2 : (1) the long-term median ΔCO/ΔFFCO 2 ratio of 14.6 ppb ppm -1 (mean: 15.5 ± 5.6 ppb ppm -1 ), (2) individual (2-)week-long integrated ΔCO/ΔFFCO 2 ratios, which take into account the large week-to-week variability of ±5.6 ppb ppm -1 (1σ; interquartile range: 5.5 ppb ppm -1 ), and (3) a calibration which also includes diurnal changes of the ΔCO/ΔFFCO 2 ratio. We show that in winter a diurnally changing ΔCO/ΔFFCO 2 ratio provides a much better agreement with the direct 14 C-based hourly ΔFFCO 2 estimates whereas summer values are not significantly improved with a diurnal calibration. Using integrated 14 CO 2 samples to determine weekly mean ΔCO/ΔFFCO 2 ratios introduces a bias in the CO-based ΔFFCO 2 estimates which can be corrected for with diurnal grab sample data. Altogether our 14 C-calibrated CO-based method allows determining ΔFFCO 2 at a semi-polluted site with a precision of approximately ±25%. DOI: 10.1111/j.1600-0889.2010.00477.x

https://www.tandfonline.com/doi/pdf/10.1111/j.1600-0889.2010.00477.x

Implication of weekly and diurnal 14C calibration on hourly estimates of CO‐based fossil fuel CO2 at a moderately polluted site in southwestern Germany

. Measurements of the mole fraction of the CO2 and its isotopes were performed in Paris during the MEGAPOLI winter campaign (January–February 2010). Radiocarbon (14CO2) measurements were used to identify the relative contributions of 77% CO2 from fossil fuel consumption (CO2ff from liquid and gas combustion) and 23% from biospheric CO2 (CO2 from the use of biofuels and from human and plant respiration: CO2bio). These percentages correspond to average mole fractions of 26.4 ppm and 8.2 ppm for CO2ff and CO2bio, respectively. The 13CO2 analysis indicated that gas and liquid fuel contributed 70% and 30%, respectively, of the CO2 emission from fossil fuel use. Continuous measurements of CO and NOx and the ratios CO/CO2ff and NOx/CO2ff derived from radiocarbon measurements during four days make it possible to estimate the fossil fuel CO2 contribution over the entire campaign. The ratios CO/CO2ff and NOx/CO2ff are functions of air mass origin and exhibited daily ranges of 7.9 to 14.5 ppb ppm−1 and 1.1 to 4.3 ppb ppm−1, respectively. These ratios are consistent with different emission inventories given the uncertainties of the different approaches. By using both tracers to derive the fossil fuel CO2, we observed similar diurnal cycles with two maxima during rush hour traffic.

/pdf/co-no-x-and-13-co-2-as-tracers-for-fossil-fuel-co-2-results-1nn7s2jpox.pdf

CO, NO x and 13 CO 2 as tracers for fossil fuel CO 2 : results from a pilot study in Paris during winter 2010

. We present an adapted gas chromatograph capable of measuring simultaneously and semi-continuously the atmospheric mixing ratios of the greenhouse gases CO2, CH4, N2O and SF6 and the trace gas CO with high precision and long-term stability. The novelty of our design is that all species are measured with only one device, making it a very cost-efficient system. No time lags are introduced between the measured mixing ratios. The system is designed to operate fully autonomously which makes it ideal for measurements at remote and unmanned stations. Only a small amount of sample air is needed, which makes this system also highly suitable for flask air measurements. In principle, only two reference cylinders are needed for daily operation and only one calibration per year against international WMO standards is sufficient to obtain high measurement precision and accuracy. The system described in this paper is in use since May 2006 at our atmospheric measurement site Lutjewad near Groningen, The Netherlands at 6°21´ E, 53°24´N, 1 m a.s.l. Results show the long-term stability of the system. Observed measurement precisions at our remote research station Lutjewad were: ±0.04 ppm for CO2, ±0.8 ppb for CH4, ±0.8 ppb for CO, ±0.3 ppb for N2O, and ±0.1 ppt for SF6. The ambient mixing ratios of all measured species as observed at station Lutjewad for the period of May 2007 to August 2008 are presented as well.

/pdf/a-single-gas-chromatograph-for-accurate-atmospheric-mixing-4igjblem29.pdf

A single gas chromatograph for accurate atmospheric mixing ratio measurements of CO2, CH4, N2O, SF6 and CO

A computer-controlled continuous air drying and flask sampling system has been developed and is discussed here. This system is set up for taking air samples automatically at remote places. Twenty glass flasks can be connected one by one or in pairs, and they can be filled at preset times, after preset intervals, or by online remote control. The system is capable of drying air continuously without operator intervention, with a flow rate of up to 4 L min−1, to a dewpoint below −50°C. This enables continuous sampling, always retaining grab air samples of, for example, the last 24 h. This way, it is possible to decide afterward, according to online instrument records, if it is worthwhile to keep a single flask sample or even the whole diurnal cycle for later analysis at the laboratory. Dry sample air can be supplied to other analyzers. Four copies of the instrumentation are active at various places in Europe and have been shown to be able to run without servicing for periods of more than 1 month.

/pdf/a-computer-controlled-continuous-air-drying-and-flask-38nmo7flkt.pdf

A Computer-Controlled Continuous Air Drying and Flask Sampling System

. We performed detailed 2H isotope diffusion measurements in the upper 3 m of firn at Summit, Greenland. Using a small snow gun, a thin snow layer was formed from 2H-enriched water over a 6 × 6 m2 area. We followed the diffusion process, quantified as the increase of the δ2H diffusion length, over a 4-year period, by retrieving the layer once per year by drilling a firn core and slicing it into 1 cm layers and measuring the δ2H signal of these layers. We compared our experimental findings to calculations based on the model by Johnsen et al. (2000) and found substantial differences. The diffusion length in our experiments increased much less over the years than in the model. We discuss the possible causes for this discrepancy and conclude that several aspects of the diffusion process in firn are still poorly constrained, in particular the tortuosity.

/pdf/constraints-on-the-d-2-h-diffusion-rate-in-firn-from-field-3ebizrr2jp.pdf

Hendrik Been

Papers

A Computer-Controlled Continuous Air Drying and Flask Sampling System

Constraints on the δ 2 H diffusion rate in firn from field measurements at Summit, Greenland