Analysis of regional CO2 contributions at the high Alpine observatory Jungfraujoch by means of atmospheric transport simulations and δ13C
Authors: Pieber Simone M. , Tuzson Béla , Henne Stephan , Karstens Ute , Gerbig Christoph , Koch Frank-Thomas , Brunner Dominik , Steinbacher Martin , Emmenegger Lukas 
Published: August 2022

Abstract. 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 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, while 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. The models captured around 40 % of
the regional CO2 variability above or below the large-scale background
and up to 35 % of the regional variability in δ13C–CO2.
This is according to expectations 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 summertime 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 large-scale 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, as well as the
most enriched values of − 17 ‰ to − 12 ‰ when impacted by
cement production emissions. Observation-based δ13Cm
values were derived independently from the simulations by a moving
Keeling-plot approach. While model-based estimates spread in a narrow range,
observation-based δ13Cm values exhibited a larger scatter and
were limited to a smaller number of data points due to the stringent
analysis prerequisites.