This paper presents a compilation of atmospheric radiocarbon for the period 1950–2019, derived from atmospheric CO2 sampling and tree rings from clean-air sites. Following the approach taken by Hua ...et al. (2013), our revised and extended compilation consists of zonal, hemispheric and global radiocarbon (14C) data sets, with monthly data sets for 5 zones (Northern Hemisphere zones 1, 2, and 3, and Southern Hemisphere zones 3 and 1–2). Our new compilation includes smooth curves for zonal data sets that are more suitable for dating applications than the previous approach based on simple averaging. Our new radiocarbon dataset is intended to help facilitate the use of atmospheric bomb 14C in carbon cycle studies and to accommodate increasing demand for accurate dating of recent (post-1950) terrestrial samples.
Monthly mean ¹⁴CO₂ observations at two regional stations in Germany (Schauinsland observatory, Black Forest, and Heidelberg, upper Rhine valley) are compared with free tropospheric background ...measurements at the High Alpine Research Station Jungfraujoch (Swiss Alps) to estimate the regional fossil fuel CO₂ surplus at the regional stations. The long-term mean fossil fuel CO₂ surplus at Schauinsland is 1.31±0.09 ppm while it is 10.96±0.20 ppm in Heidelberg. No significant trend is observed at both sites over the last 20 years. Strong seasonal variations of the fossil fuel CO₂ offsets indicate a strong seasonality of emissions but also of atmospheric dilution of ground level emissions by vertical mixing.
Radiocarbon (14C) is a powerful tracer of fossil emissions because fossil fuels are entirely depleted in 14C, but observations of 14CO2 and especially 14CH4 in urban regions are sparse. We present ...the first observations of 14C in both methane (CH4) and carbon dioxide (CO2) in an urban area (London) using a recently developed sampling system. We find that the fossil fraction of CH4 and the atmospheric concentration of fossil CO2 are consistently higher than simulated values using the atmospheric dispersion model NAME coupled with emission inventories. Observed net biospheric uptake in June–July is not well correlated with simulations using the SMURF model with NAME. The results show the partitioning of fossil and biospheric CO2 and CH4 in cities can be evaluated and improved with 14C observations when the nuclear power plants influence is negligible.
Plain Language Summary
Radiocarbon (14C) is an ideal tracer of fossil emissions, as fossil fuels have lost all 14C during millions of years of burial underground. When fossil carbon is re‐introduced into the atmosphere, it exerts a strong dilution of the radiocarbon to total carbon ratio. By measuring this ratio in the atmosphere, we can quantify fossil methane and carbon dioxide emissions. This is the first combined study of 14C in both atmospheric methane and carbon dioxide at regional scale.
Key Points
Atmospheric radiocarbon measurements in central London reveal higher fossil CH4 and CO2 present, compared to simulations
Radiocarbon measurements show biospheric uptake of CO2 in July that is stronger than simulations
Nuclear power plants interfere with radiocarbon measurements in London when air is coming from Europe
Since the 1950s, observations of radiocarbon (14C) in tropospheric carbon dioxide (CO2) have been conducted in both hemispheres, documenting the so-called nuclear “bomb spike” and its transfer into ...the oceans and the terrestrial biosphere, the two compartments permanently exchanging carbon with the atmosphere. Results from the Heidelberg global network of Δ14C-CO2 observations are revisited here with respect to the insights and quantitative constraints they provided on these carbon exchange fluxes. The recent development of global and hemispheric trends of Δ14C-CO2 are further discussed in regard to their suitability to continue providing constraints for 14C-free fossil CO2 emission changes on the global and regional scale.
Ingeborg Levin (1953-2024) Vogel, Felix; Hammer, Samuel
Science (American Association for the Advancement of Science),
2024-Mar-29, 2024-03-29, 20240329, Letnik:
383, Številka:
6690
Journal Article
Independent verification of greenhouse gas emissions reporting is a legal requirement of the Kyoto Protocol, which has not yet been fully accomplished. Here, we show that dedicated long-term ...atmospheric measurements of greenhouse gases, such as carbon dioxide (CO 2 ) and methane (CH 4 ), continuously conducted at polluted sites can provide the necessary tool for this undertaking. From our measurements at the semi-polluted Heidelberg site in the upper Rhine Valley, we find that in the catchment area CH 4 emissions decreased on average by 32 ± 6% from the second half of the 1990s until the first half of the 2000s, but the observed long-term trend of emissions is considerably smaller than that previously reported for southwest Germany. In contrast, regional fossil fuel CO 2 levels, estimated from high-precision 14 CO 2 observations, do not show any significant decreasing trend since 1986, in agreement with the reported emissions for this region. In order to provide accurate verification, these regional measurements would best be accompanied by adequate atmospheric transport modelling as required to precisely determine the relevant catchment area of the measurements. Furthermore, reliable reconciliation of reported emissions will only be possible if these are known at high spatial resolution in the catchment area of the observations. This information should principally be available in all countries that regularly report their greenhouse gas emissions to the United Nations Framework Convention on Climate Change.
Brown carbon is a ubiquitous and unidentified component of organic aerosol which has recently come into the forefront of atmospheric research. This component is strongly linked to the class of ...humic‐like substances (HULIS) in aerosol whose ultimate origin is still being debated. Using a simplified spectroscopic method the concentrations of brown carbon have been determined in aqueous extracts of fine aerosol collected during the CARBOSOL project. On the basis of the results of 2‐year measurements of several aerosol constituents at six European sites, possible sources of brown carbon are inferred. Biomass burning (possibly domestic wood burning) is shown to be a major source of brown carbon in winter. At elevated sites in spring, smoke from agricultural fires may be an additional source. Direct comparison of measured brown carbon concentrations with HULIS determined by an independent method reveals that the two quantities correlate well at low‐elevation sites throughout the year. At high‐elevation sites the correlation is still high for winter but becomes markedly lower in summer, implying different sources and/or atmospheric sinks of brown carbon and HULIS. The results shed some light on the relationships between atmospheric brown carbon and HULIS, two ill‐defined and overlapping components of organic aerosol.
Quantifying carbon dioxide emissions from fossil fuel burning (FFCO
2
) is a crucial task to assess continental carbon fluxes and to track anthropogenic emissions changes in the future. In the ...present study, we investigate potentials and challenges when combining observational data with simulations using high-resolution atmospheric transport and emission modelling. These challenges concern, for example, erroneous vertical mixing or uncertainties in the disaggregation of national total emissions to higher spatial and temporal resolution. In our study, the hourly regional fossil fuel CO
2
offset (ΔFFCO
2
) is simulated by transporting emissions from a 5 min×5 min emission model (IER2005) that provides FFCO
2
emissions from different emission categories. Our Lagrangian particle dispersion model (STILT) is driven by 25 km×25 km meteorological data from the European Center for Medium-Range Weather Forecast (ECMWF). We evaluate this modelling framework (STILT/ECMWF+IER2005) for the year 2005 using hourly ΔFFCO
2
estimates derived from
14
C, CO and
222
Radon (
222
Rn) observations at an urban site in south-western Germany (Heidelberg). Analysing the mean diurnal cycles of ΔFFCO
2
for different seasons, we find that the large seasonal and diurnal variation of emission factors used in the bottom-up emission model (spanning one order of magnitude) are adequate. Furthermore, we show that the use of
222
Rn as an independent tracer helps to overcome problems in timing as well as strength of the vertical mixing in the transport model. By applying this variability correction, the model-observation agreement is significantly improved for simulated ΔFFCO
2
. We found a significant overestimation of ΔFFCO
2
concentrations during situations where the air masses predominantly originate from densely populated areas. This is most likely caused by the spatial disaggregation methodology for the residential emissions, which to some extent relies on a constant per capita-based distribution. In the case of domestic heating emissions, this does not appear to be sufficient.
Long-term measurements of atmospheric Δ
14
CO
2
from two monitoring stations, one in the European Alps (Jungfraujoch, Switzerland) and the other in the Black Forest (Schauinsland, Germany), are ...presented. Both records show a steady decrease, changing from about 6‰ per year at the beginning of the century to only 3‰ per year on average in the last 4 yr. A significant seasonal variation of Δ
14
CO
2
is observed at both sites with maxima during late summer and minima in late winter/early spring. While the Δ
14
C maxima are similar at Jungfraujoch and Schauinsland, the minima at Schauinsland are lower by up to 10‰, due to a larger influence from
14
C-free fossil fuel CO
2
emissions in the footprint of the Schauinsland station in winter. Summer mean Δ
14
C values at Schauinsland are considered best suited as input for studies of biospheric carbon cycling in mid-northern latitudes or for dating of organic material of the last half century.
The direct way to estimate the regional fossil fuel CO
2
surplus (ΔffCO
2
) at a station is by measuring the Δ
14
CO
2
depletion compared with a respective background. However, this approach has ...several challenges, which are (i) the choice of an appropriate Δ
14
CO
2
background, (ii) potential contaminations through nuclear
14
CO
2
emissions and (iii) masking of ΔffCO
2
by
14
C-enriched biosphere respiration. Here we evaluate these challenges and estimate potential biases and typical uncertainties of
14
C-based ΔffCO
2
estimates in Europe. We show that Mace Head (MHD), Ireland, is a representative background station for the Integrated Carbon Observation System (ICOS) atmosphere station network. The mean ΔffCO
2
representativeness bias when using the MHD Δ
14
CO
2
background for the whole observation network is of order 0.1 ± 0.3 ppm. At ICOS sites, the median nuclear contamination leads to 25% low-biased ΔffCO
2
estimates if not corrected for. The ΔffCO
2
masking due to
14
C-enriched heterotrophic CO
2
respiration can lead to similar ΔffCO
2
biases as the nuclear contaminations, especially in summer. Our evaluation of all components contributing to the uncertainty of ΔffCO
2
estimates reveals that, due to the small ffCO
2
signals at ICOS stations, almost half of the
14
C-based ΔffCO
2
estimates from integrated samples have an uncertainty that is larger than 50%.
This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.
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