Analysis of regional CO<sub>2</sub> contributions at the high Alpine observatory Jungfraujoch by means of atmospheric transport simulations and δ<sup>13</sup>C

Abstract

Abstract. Understanding of regional greenhouse gas emissions into the atmosphere is a prerequisite to mitigate climate change. In this study, we investigated the regional contributions of carbon dioxide (CO2) at the location of the high Alpine observatory Jungfraujoch ("JFJ", Switzerland, 3580 m a.s.l.). To this purpose, we combined receptor-oriented atmospheric transport simulations for CO2 concentration in the period of 2009–2017 with stable carbon isotope (δ13C-CO2) information. We applied two Lagrangian particle dispersion models driven by output from two different numerical weather prediction systems (FLEXPART-COSMO and STILT-ECMWF) in order to simulate CO2 concentration at JFJ based on regional CO2 fluxes, to estimate atmospheric δ13C-CO2, and to obtain model-based estimates of the mixed source signatures (δ13Cm). Anthropogenic fluxes were taken from a fuel type-specific version of the EDGAR v4.3 inventory and ecosystem fluxes were based on the Vegetation Photosynthesis and Respiration Model (VPRM). The simulations of CO2, δ13C-CO2 and δ13Cm were then compared to observations performed by quantum cascade laser absorption spectroscopy. Around 40 % of the regional CO2 variability above or below the large-scale background was captured by the models, and up to 35 % of the regional variability in δ13C-CO2. This is remarkable considering the complex Alpine topography, the low intensity of regional signals at JFJ, and the challenging measurements. Best agreement between simulations and observations in terms of short-term variability and intensity of the signals for CO2 and δ13C-CO2 was found between late autumn and early spring. The agreement was inferior in the early autumn periods and during summer. This may be associated with the atmospheric transport representation in the models. In addition, the net ecosystem exchange fluxes are a possible source of error, either through inaccuracies in their representation in VPRM for the (Alpine) vegetation or through a day (uptake) vs. night (respiration) transport discrimination to JFJ. Furthermore, the simulations suggest that JFJ is subject to relatively small regional anthropogenic contributions, due to its remote location (elevated and far from major anthropogenic sources), and the limited planetary boundary layer-influence during winter. Instead, the station is primarily exposed to summer-time ecosystem CO2 contributions, which are dominated by rather nearby sources (within 100 km). Even during winter, simulated gross ecosystem respiration accounted for approximately 50 % of all contributions to the CO2 concentrations above the largescale background. The model-based monthly mean δ13Cm ranged from −22 ‰ in winter to −28 ‰ in summer and reached the most depleted values of −35 ‰ at higher fractions of natural gas combustion, and the most enriched values of −17 to −12 ‰ when impacted by cement production emissions. Observation-based δ13Cm values derived by a moving Keeling-plot approach were in good agreement with the model-based estimates. They exhibited a larger scatter, while model-based estimates spread in a more narrow range. Overall, observation-based δ13Cm were limited to a smaller number of data points compared to model-based estimates owing to the stringent analysis prerequisites in combination with the low regional signal at JFJ.

IRIS analyser assessment reveals sub-hourly variability of isotope ratios in carbon dioxide at Baring Head, New Zealand's atmospheric observatory in the Southern Ocean

“…15, C), which Zobitz et al, (2006) reported as an acceptable uncertainty level. For further comparison, Pieber et al, (2021) filter their multi-year data to exclude CO2 variations < 3 ppm and cluster their data for intercept uncertainties of 1, 2, 3 and 4 ‰, which indicates the performance of their instrument is superior to that of the Delta Ray system presented here. Zobitz et al, (2006) model the improvement in the uncertainty of the intercepts with improvement of the measurement precision for isotope ratios.…”

“…The potential for field-deployable, laser-based instruments measuring both mole fractions and isotope ratios in atmospheric CO2 in real-time has been demonstrated (Bowling et al, 2003;Mohn et al, 2007). Continuous technical improvement of both analysers and applied calibration techniques enables an achievable measurement precision that is increasingly comparable to that of well-performing IRMS systems (Tuzson et al, 2011;Griffith et al, 2012;Sturm et al, 2013;Hammer et al, 2013;Flores et al, 2017;Pieber et al, 2021) and is approaching the compatibility goal of the World Meteorological Organisation (WMO), (Steur et al, 2021). With that, laser-based instruments may be an interesting alternative for observations that were previously limited to IRMS laboratories and flask sampling programmes.…”

“…With that, laser-based instruments may be an interesting alternative for observations that were previously limited to IRMS laboratories and flask sampling programmes. The performance of these techniques was demonstrated in the monitoring of annual and seasonal cycles with high temporal resolution (Sturm et al, 2013;Vardag et al, 2016;Pieber et al, 2021). Moreover, real-time measurements of CO2 and its stable isotopes opens new research opportunities that researchers have hitherto not been able to explore.…”

“…Moreover, real-time measurements of CO2 and its stable isotopes opens new research opportunities that researchers have hitherto not been able to explore. For example, the high temporal resolution achievable with laser-based instruments enables observations ranging from synoptic scales (Vardag et al, 2015;Vardag et al, 2016;Pieber et al, 2021) to that of micrometeorological observations (Griffis et al, 2008;Wehr et al, 2013), for which IRMS based techniques are not a feasible long-term solution.…”

“…We tested the Delta Ray instrument in our laboratory and at Baring Head (BHD), our observatory for Southern Ocean background air (Brailsford et al, 2012). Generally, Southern Ocean background air shows very little variability in CO2 mole fractions (Stephens et al, 2013;Steinkamp et al, 2017) and isotope ratios (Allison and Francey, 2007;Moss et al, 2018), providing one of the most challenging environments to explore the performance of a field-deployed instrument for such measurements (Pieber et al, 2021). We compare Delta Ray data with co-located observations of CO2 mole fractions in the context of meteorology and the variability of Radon.…”