The ratios of atmospheric tracers are often used to interpret the local CO2 budget, where measurements at a single height are assumed to represent local flux signatures. Alternatively, these signatures can be derived from direct flux measurements or using fluxes derived from measurements at multiple heights. In this study, we contrast interpretation of surface CO2 exchange from tracer ratio measurements at a single height versus measurements at multiple heights. Specifically, we analyse the ratio between atmospheric O2 and CO2 (exchange ratio, ER) above a forest canopy. We consider two alternative approaches: the exchange ratio of the forest (ERforest) obtained from the ratio of the surface fluxes of O2 and CO2, derived from their vertical gradients measured at multiple heights, and the exchange ratio of the atmosphere (ERatmos) obtained from changes in the O2 and CO2 mole fractions over time measured at a single measurement height. We investigate the diurnal cycle of both ER signals, with the goal to relate the ERatmos signal to the ERforest signal and to understand the biophysical meaning of the ERatmos signal. We combined CO2 and O2 measurements from Hyytiälä, Finland during spring and summer of 2018 and 2019 with a conceptual land-atmosphere model and a theoretical relationship between ERatmos and ERforest to investigate the behaviour of ERatmos and ERforest during different environmental conditions. We show that the ERatmos signal rarely directly represents the forest exchange, mainly because it is influenced by entrainment of air from the free troposphere into the atmospheric boundary layer. The resulting ERatmos signal is not the average of the contributing processes, but rather an indication of the influence of large scale processes such as entrainment or advection. We conclude that the ERatmos only provides a weak constraint on local scale surface CO2 exchange, because large scale processes confound the signal. Single height measurements therefore always require careful selection of the time of day and should be combined with atmospheric modelling to yield a meaningful representation of forest carbon exchange. More generally, we recommend to always measure at multiple heights when using multi-tracer measurements to study surface CO2 exchange.

How to cite: Faassen, K., Luijkx, I., Vilà-Guerau de Arellano, J., González-Armas, R., Heusinkveld, B., Mammarella, I., and Peters, W.: Atmospheric O2 and CO2 measurements at a single height provide weak constraint on the surface carbon exchange., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10052, https://doi.org/10.5194/egusphere-egu24-10052, 2024.

Climate change is intricately linked to the carbon cycle. Both phenomena are examined across various temporal and spatial scales to clarify the processes of carbon exchange between the atmosphere and the Earth's surface in response to increasing greenhouse gas emissions, primarily CO₂. Anthropogenic CO₂ emissions emerge as the main driver of global warming, while natural CO₂ emissions into the atmosphere constitutes approximately 1% of annual CO₂ emissions, mainly resulting from volcanic activity.

This study relies on datasets gathered during surveys at Etna volcano and the Madonie mountains, Italy, to identify spatial variations in stable isotope composition and the concentration of airborne CO₂. The dataset was collected along a path specifically designed from the urban areas of Catania and Cefalù, both in Italy, to high altitudes (i.e., ~2200 m a.s.l.) at Mount Etna and the Madonie mountains, Italy, respectively. This dataset facilitates exploration of spatial variations in the sources of atmospheric CO₂ and patterns in the isotopic composition and concentration of airborne CO₂ with altitude.

The study's findings indicate that the primary sources of airborne CO₂ exhibit a biogenic isotopic carbon signature at Etna and the Madonie mountains, although a more ¹³C-enriched CO₂ source influences the isotopic signature of airborne CO₂ at Mount Etna. The concentration of airborne CO₂ and the carbon isotopic signature remain independent of altitude. However, a high correlation between altitude and oxygen isotopic signature suggests that variations in hydrology significantly impact the airborne CO₂.

Furthermore, the study underscores the complex relationship between environmental variables and airborne CO₂ concentration, indicating that the pattern in airborne CO₂ cannot be comprehensively investigated solely through concentration analysis due to the high background CO₂ concentration compared to relative spatial variations. Additionally, the carbon isotopic signature of CO₂ enables the differentiation of multiple sources of CO₂ at Mount Etna and the distinction of ¹³C-enriched volcanic CO₂ from background air at low airborne CO₂ concentrations.

How to cite: Gurrieri, S. and Di Martino, R. M. R.: Spatial Isotopic Analysis of Airborne CO2: Insights from Etna Volcano and Madonie Mountains, Italy, Surveys, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5556, https://doi.org/10.5194/egusphere-egu24-5556, 2024.

Bulk isotope analytical methods of CH₄ quantify carbon and hydrogen isotope ratios (δ¹³C and δD) to provide information on the sources and sinks of CH₄ in natural environments. A more extensive tracing of CH₄ pathways, especially when multiple processes and sources are involved, has been realized by novel measurements techniques capable of methane clumped isotope analysis (termed as Δ¹³CH₃D and Δ¹²CH₂D₂) during the past decade. These paired datasets can either be used as proxy for exploring CH₄ formation temperatures under thermodynamic equilibrium, or studying contributions of kinetically controlled processes during CH₄ formation and consumption¹.

Currently, methane clumped isotope analysis is performed by two different techniques: isotope-ratio mass spectrometry (e.g. 253 Ultra from Thermo Fisher Scientific² or Panorama from Nu Instruments¹) or laser absorption spectroscopy (e.g. QCLAS from Aerodyne Research^3,4), both of which have demonstrated a precision better than 0.5‰ for Δ¹³CH₃D and 1.5‰ for Δ¹²CH₂D₂, which is sufficient for most applications. This work will provide insights about the main instrumental features, measurement protocols and performance of the 253 Ultra HR-IRMS at Tokyo Institute of Technology (Japan)^2,5, and the QCL absorption spectrometer at Empa (Switzerland)⁴. Furthermore, advantages and limitations of both techniques during current applications in natural methane samples are discussed. Finally, perspectives for future applications at low CH₄ concentrations, such as atmospheric monitoring, are provided.

References:

• Young et al., 2017, Geochimica et Cosmochimica Acta; 2. Dong et al., 2020, Thermo Scientific white paper; 3. Gonzalez et al., 2019, Analytical Chemistry; 4. Prokhorov and Mohn, 2022, Analytical Chemistry; 5. Zhang et al., 2021, Geochimica et Cosmochimica Acta

How to cite: Zhang, N., Prokhorov, I., Kueter, N., Bernasconi, S., Nakagawa, M., Gilbert, A., Ueno, Y., Tuzson, B., Emmenegger, L., and Mohn, J.: Pros and cons of methane clumped isotope analysis by high-resolution isotope-ratio mass spectrometry and laser absorption spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20240, https://doi.org/10.5194/egusphere-egu24-20240, 2024.

How to cite: Botía, S., Komiya, S., Jones, S. P., Chanca, I., Horna, V., Dajti, G., Adnew, G. A., Bulthuis, S., Schöngart, J., Fernandez Piedade, M. T., Wittmann, F., Marra, D. M., Rothe, M., Mossen, H., Jordan, A., Röckmann, T., Lavric, J., Sierra, C., Trumbore, S., and van Asperen, H.: Characterization of the isotopic signature in methane from several biogenicsources in the central Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21410, https://doi.org/10.5194/egusphere-egu24-21410, 2024.

Mercury (Hg) is highly toxic and the only heavy metal that can exist in the atmosphere in gaseous form. When atmospheric Hg mixes with aerosols, it forms particulate-bound mercury (PBM). PBM can be transported and settle down quickly across regions, posing serious threats to ecosystems globally. Despite these concerns, tracking the sources and transport of atmospheric Hg remains challenging due to its global dispersal nature. However, the three-dimensional fractionation of Hg isotopes provides a feasible approach for addressing this issue. In this study, PBM_2.5 and PBM_TSPsamples were collected simultaneously in rural, suburban, urban, industrial, and coastal areas of the Beijing-Tianjin-Hebei (BTH) region, which is influenced by severe atmospheric pollution and the East Asian monsoon. Due to the significant influence of anthropogenic sources, the concentrations of PBM_2.5 and PBM_TSP were highest in the industrial and coastal areas, followed by the urban, suburban, and rural areas. The δ²⁰²Hg values of PBM_2.5 and PBM_TSP at the five sites were negative, overlapping with the values of most anthropogenic sources. However, most PBM_2.5 and PBM_TSP samples showed significantly positive Δ¹⁹⁹Hg, significantly higher than the values of emission sources,especially for PBM_2.5. The mass-independent fractionation (MIF) of Hg and sulfur isotopes showed that strong photochemical reduction happened during long-distance transport, making Δ¹⁹⁹Hg have a positive shift. The positive changes in Δ²⁰⁰Hg may be due to ozone-mediated oxidation during the transport process, as shown by the interesting relationships between O₃, Δ¹⁹⁹Hg, and Δ²⁰⁰Hg in PBM_2.5. Additionally, the analysis of backward trajectories unveiled the influence of air masses originating northwest of the BTH region through high-altitude transport. The cross-border transport of PBM, influenced by westerly and northwesterly air masses from Central Asia and Russia, markedly impacted  PBM pollution in the BTH region. Furthermore, these air masses, upon reaching the BTH area, would transport heightened PBM concentrations to the ocean through the winter monsoon. Conversely, during the summer, southeastward air masses transported from the ocean by the summer monsoon acted to mitigate the inland PBM pollution. The study results show that significant positive odd-MIF of PBM can occur in places with intensive anthropogenic emissions rather than being limited to remote areas. It implies that the odd-MIF resulting from atmospheric transport has likely been significantly undervalued. Our research offers valuable perspectives on the transport, transformation, and circulation of Hg in the environment.

How to cite: Qin, X., Dong, X., Liu, C., Wei, R., Tao, Z., Zhang, H., and Guo, Q.: Mass-Independent Fractionation Reveals the Sources and Transport of Atmospheric Particulate Bound Mercury, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3338, https://doi.org/10.5194/egusphere-egu24-3338, 2024.

Photolysis of snowpack nitrate results in emission of the reactive nitrogen species NO_x and HONO. These are important pre-cursors of HO_x radicals and ozone, and thereby affect the oxidising capacity of the lower atmosphere above remote snow-covered areas. This is of particular importance in the polar regions as the usual OH radical formation pathway (ozone photolysis and reaction of O(¹D) with H₂O) is limited by the low water vapour concentration. Isotope analysis of atmospheric reactive nitrogen species and snow nitrate is proving to be a crucial tool for elucidating mechanisms of reactive nitrogen cycling in and above snow.

The first snowpit profiles of nitrate stable isotopes (δ¹⁵N, δ¹⁸O) and concentration at Halley VI Research Station in coastal Antarctica will be presented. The observed isotope fractionation provides evidence of photochemical loss of nitrate and allows estimation of the photolytic isotope fractionation constant at the site. At this high accumulation site, the peak in nitrate concentration from the previous summer is preserved below the snow surface, unlike at low accumulation sites on the Antarctic Plateau. Combining measurements of nitrate concentration and its isotopic compositions preserved in snow helps disentangle the isotope signature of seasonal changes in atmospheric nitrate sources from post-depositional isotope fractionation occurring even at high snow accumulation sites.

How to cite: Bond, A., Frey, M. M., Kaiser, J., Marca, A., and Squires, F.: Isotope analysis of snowpack nitrate in coastal Antarctica; evidence of nitrate photolysis and preservation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-548, https://doi.org/10.5194/egusphere-egu24-548, 2024.

Air pollution has become a serious problem in some parts of the world. The mechanism of sulfate formation during haze events is still not clear. This research looks at the different sulfur isotope compositions of sulfate in PM_2.5 (from 2015 to 2016) in Beijing and in seasonal samples of PM_2.5, PM_1.0, and TSP from rural, suburban, urban, industrial, and coastal areas of North China (in 2017). The goal is to figure out the mechanism by which SO₂ oxidizes at different levels of air pollution. An obvious seasonal variation (with positive values in spring, summer, and autumn and negative values in winter) is shown by the Δ³³S values of sulfate in aerosols, except for those samples collected in rural areas. The Δ³³S value (S-MIF) of sulfate in PM_2.5 shows a pronounced seasonality, with positive values in spring, summer, and autumn and negative values in winter. The negative Δ³³S changes that happen during winter haze events are mostly caused by SO₂ being oxidized by H₂O₂ and transition metal ion catalysis (TMI) in the troposphere, which is most likely caused by coal burning. The positive Δ³³S results observed on clean days are mainly attributed to tropospheric SO₂ oxidation and stratospheric SO₂ photolysis. These results provide important information on sulfate formation during haze events and clean days.

How to cite: Guo, Q., Han, X., Dong, X., Qin, X., and Wei, R.: Sulfate formation in haze pollution using multiple sulfur isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4515, https://doi.org/10.5194/egusphere-egu24-4515, 2024.

Stable isotope analysis of water ²H₂O and H₂¹⁸O are powerful tracers to understand the different hydrological processes like ecohydrological processes, and hydroclimatic processes [1]. The measurement of δ²H and δ¹⁸O in water samples using laser-based absorption techniques is adopted increasingly in hydrologic and environmental studies. In contrast to the conventional Isotope ratio mass spectrometry (IRMS) technique, optical absorption spectroscopic techniques allow the realization of isotopologue-specific, non-destructive, and compact spectrometers with short analysis times with high-precision capabilities.

ABB’s ultraportable water analyzers are compact, portable field-deployable laser spectrometers capable of making continuous, high-frequency measurements of δ¹⁸O and δ²H from multiple water sources. The instrument is based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technique [2]. These analyzers are capable of measuring liquid water (GLA132-LWIA) or vapor (GLA132-WVIA).  They are rugged and designed to handle both natural and isotopically enriched water samples.  Users can leverage the precision and speed of the GLA132-LWIA by coupling it with a portable auto-injector to perform automated, unattended injection patterns on multiple samples.

An important asset of this innovative approach based on OA-ICOS technology coupled with the portable auto-injector technology is its sample throughput, which allows one to measure approximately 90 samples a day corresponding to 720 injections each with a sample volume of 0.5 µL per injection per day. The precision (1σ) achieved corresponds to 0.6 ‰ for δ²H and 0.2 ‰ for δ¹⁸O. The analyzer’s ease of use, field portability, durability, and high throughput make it an excellent choice for reliable, high-performance measurement of freshly collected samples in the field, thereby opening a plethora of applications to understand the different processing governing the earth’s climate.

[1] Tian, C.,et al., Sci Rep 8, 6712 (2018). https://doi.org/10.1038/s41598-018-25102-7

[2] A. O’Keefe, et al., Chemical Physics Letters, vol. 307, no. 5, pp. 343–349, Jul. 1999, doi: 10.1016/S0009-2614(99)00547-3.

How to cite: Nataraj, A., Fortson, S., Despagne, F., Lobo Neto, J., and Baer, D.: Laser absorption spectroscopy-based ultraportable analyzer for δ18O and δ2H in water., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13866, https://doi.org/10.5194/egusphere-egu24-13866, 2024.

We present a project aiming to provide a new estimate of the parameter known as "climate sensitivity" (symbol γ_L in the models) which is essential to constrain models of future climate change. This parameter describes how the amount of carbon sequestered by terrestrial ecosystems depends on temperature. Predictions of future climate by models show significant uncertainties associated with the estimates of carbon sequestration by terrestrial ecosystems with future temperature increases. Quantifying γ_L with data measured in the industrial era is very complicated because the terrestrial part of the carbon cycle is dominated by the effect of the increase in atmospheric CO₂ (the so-called anthropogenic “fertilization” or CO₂ concentration feedback, symbol β_L in the models), while the effect of temperature is smaller. We will derive γ_L from measurements of ultra-trace gases trapped in polar ice cores in pre-industrial times.

The Little Ice Age (i.e. the period that roughly covers the centuries 1400-1800 AD) was characterized by temperatures lower than the average of the last millennium, due to intense volcanic activity and reduced solar activity. The global decrease in temperature has coincided with a decrease in the atmospheric concentration of CO₂, mainly caused by sequestration from terrestrial ecosystems. Low CO₂ concentrations contributed negligibly to the decrease in temperature, making the Little Ice Age a suitable time to derive γ_L.

Why CO2 decreased during the Little Ice Age is debated. On the one hand, considerations deriving from models that simulate the amount of carbon present in terrestrial ecosystems suggest that primary productivity increased during the Little Ice Age because of an anthropogenic effect. This increase would have been caused by pandemics and colonial conquests in America which led to a depopulation of cultivated lands and a regrowth of tree species. On the other hand, measurements of carbonyl sulphate (COS) and numerical calculations capable of closing the COS budget suggest that primary productivity naturally decreased during the Little Ice Age. In this second case, the decrease in CO₂ would be caused by the fact that the respiration of terrestrial ecosystems decreased to a greater extent than the decrease in primary productivity. Therefore, if this second hypothesis is correct, it would be possible to derive γ_L from COS data covering the Little Ice Age.

Unfortunately, COS measurements covering the Little Ice Age have great uncertainty. It is therefore necessary to carry out new measurements of COS concentration during the Little Ice Age. The COS measurements will be accompanied by CO₂ and δ¹³C-CO₂ measurements, necessary to confirm, on the one hand, the working hypothesis, and, on the other, the quality of the ice samples used. Finally, future developments could build on measurements of COS isotopes in ice samples.

Rubino M., et al. Terrestrial uptake due to cooling responsible for low atmospheric CO₂ during the Little Ice Age, Nature Geoscience, 9, 691-694 (2016)

How to cite: Iazzetta, D. and Rubino, M.: Quantification of the climate sensitivity of terrestrial ecosystems through the analysis of ultra-trace gases in ice cores over the last millennium, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7270, https://doi.org/10.5194/egusphere-egu24-7270, 2024.

Anthropogenically emitted CO₂ is warming the earth’s climate to temperatures that already exceed pre-industrial levels by more than 1.2 ^oC. Terrestrial vegetation has slowed the rate of climate change by removing part of this anthropogenic emission. Accurate estimations of the present and future terrestrial carbon sink are still needed for forecasting climate and for informing policies for climate stabilization. This requires precise knowledge of the photosynthetic C uptake over land (gross primary production, GPP), independently of the C released through plant and soil respiration. The gas carbonyl sulfide (COS) has emerged as a promising tracer for GPP. This is because both CO₂ and COS are a substrate for carbonic anhydrase (CA), the first enzyme involved in photosynthesis, so that the uptake by foliage of COS and CO₂ often covaries. Estimating GPP from COS measurements and atmospheric budgets also requires quantifying ocean and industrial COS sources, which is challenging. Isotopic constrained COS tropospheric mass balances can help quantify the relative contribution of these sources if the isotope discrimination during COS uptake by terrestrial vegetation (the main COS sink) is known. However, little is known about plant-atmosphere COS isotope exchange; measurements are challenging and theory to interpret these measurements is limited. Herein, we present a new comprehensive model for discrimination during COS uptake by plants (∆³⁴S) and use it to revisit existing COS isotope datasets and atmospheric budgets. Our ∆³⁴S model expands Davidson et al. (2022) pioneer framework by accounting for leaf COS production. By analogy with the well-established model for photosynthetic discrimination against ¹³CO₂, Davidson et al. ∆³⁴S model stated that COS discrimination occurs as COS diffuses into the leaf and binds to CA. Leaf COS emission was not considered, although it has been reported in species ranging from bryophytes to wheat and trees. Because it is uncertain where these emissions occur, we tested different leaf-level COS emission scenarios - including zero emissions - in various leaf compartments (cuticle, intercellular space, cytosol), alone or in combination. We used this comprehensive model to generate predictions for ∆³⁴S in C₃ and C₄ species and discussed implications for determining a global plant uptake fractionation factor. Our mechanistic model provides a framework to interpret vegetation-atmosphere COS isotope exchange that can prove useful to improve COS uptake-based GPP estimates and our understanding of plant function, especially when combined with other isotopes (C, O, H).

How to cite: Ubierna, N., Baartman, S. L., Popa, M. E., Ogée, J., Krol, M. C., and Wingate, L.: A comprehensive model for COS isotope discrimination during leaf COS uptake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10688, https://doi.org/10.5194/egusphere-egu24-10688, 2024.

The gross primary productivity (GPP), which represents the gross uptake of carbon dioxide (CO²) by plants, cannot be directly measured at the ecosystem level. It must instead be inferred either by applying models or by measuring proxies. A notable proxy is the trace gas carbonyl sulfide (COS), which is particularly interesting because it follows a pathway into plant leaves similar to CO² and, unlike CO², is generally not reemitted.

To utilize COS as a tracer for GPP, the leaf relative uptake (LRU)—the ratio of the deposition velocities of COS to CO² at the leaf level—must be known a priori. Initial studies suggested that LRU values were relatively constrained, around 1.7. However, it has been observed that LRU varies between plant species and is influenced by environmental factors such as drought, vapor pressure deficit (VPD), and photosynthetically active radiation (PAR).

The variation in LRU related to PAR is due to COS primarily being catalyzed by the enzyme carbonic anhydrase in a light-independent reaction, contrasting with CO² uptake via photosynthesis, which is dependent on PAR. Consequently, LRU increases under lower light conditions, even when stomatal control on both gases is similar.

This light dependency prompts questions about LRU variation within canopies. While most LRU chamber measurements have been conducted under laboratory conditions or in canopy crowns, additional data on LRU variability within canopies, particularly in lower light conditions, are necessary. A comprehensive understanding of LRU, encompassing both crown and shadow-adapted leaves at various canopy positions and considering stand species composition, is essential for accurately calculating GPP at the ecosystem scale using eddy covariance (EC) measurements.

To investigate how LRU varies within the canopy, particularly in response to environmental factors like PAR and VPD, and to compare the LRUs from different chamber measurements to EC measurements, we conducted a measurement campaign in an Austrian Pine forest. This included ongoing eddy covariance measurements of COS, CO², and H²O, supplemented by manual measurements of the same gases using branch chambers at three levels within the Pinus sylvestris canopy and three additional chambers of Juniperus communis.

Above 400 µmol photons m² s PAR, where we consider the LRU to be light independent, the LRU reached 1.61±0.3 at the top of the crown and decreased to 1.55±0.4 and 1.56±0.3 going consecutively deeper into the canopy of Pinus sylvestris. In contrast, the LRU of Juniperus communis in the understory was notably lower, at 1.41±0.4. Between 100 and 400 µmol photons m² s PAR, the LRUs increased to 1.81±0.3 and 1.69±0.5 for the upper and middle canopy layers, respectively, while decreasing to 1.43±0.2 and 1.19±0.2 in the lower parts of Pinus sylvestris and Juniperus communis, respectively. This decrease in LRU deeper within the canopy is attributed to a greater reduction in COS compared to CO² deposition velocity of the leaves. The median LRU above 800 µmol photons m² s PAR, based on classical daytime flux partitioning for the summer month of 2022, was 2.5±0.7, indicating the need for further investigation into the observed discrepancy in LRU.

How to cite: Spielmann, F. M., Hammerle, A., Scholz, K., Putz, G., Hänchen, L., De-Vries, A., and Wohlfahrt, G.: From over to under, a story about the vertical within-canopy variation of the leaf relative uptake rate of COS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16015, https://doi.org/10.5194/egusphere-egu24-16015, 2024.