Sophia Louise Baartman

Long‐term carbon flux measurements at the FLUXNET site Loobos, a Pine forest in the Netherlands, reveal a counter‐intuitive decline in total ecosystem respiration ( TER ) by tens of percents between 1997 and 2021. This trend cannot be explained by temperature variability or methodological changes alone. Instead, our findings point to a biogeochemical mechanism: despite a doubling of soil organic matter stocks, ecosystem respiration appears limited by decomposition rates rather than substrate availability. Soil incubation experiments indicate that microbial activity is limited by substrate quality and strongly acidic conditions (pH = 2.9), associated with large nitrogen deposition. Glucose addition experiments confirm the presence of an active microbiome, but its activity is suppressed under the present acidic soil conditions. These results raise concerns about ecosystem health under conditions of nitrogen deposition and the long‐term sustainability of the observed carbon sink. Loobos may serve as an early indicator of broader ecosystem responses to environmental disturbances, as similar negative TER trends have been observed at other long‐term FLUXNET sites. To advance understanding of the global carbon cycle, it is essential that observed flux trends are attributed and corroborated by changes in carbon and nitrogen stocks, and that models are continuously confronted with observational data. We therefore discuss the need of periodically measuring pH as soil acidification can be a limiting factor and suggest the need to introduce this variable in model representations of TER near regions sensitive to nitrification.

Background Carbonyl Sulfide (COS) is a potential tracer for estimating gross primary productivity (GPP), due to its co-uptake with CO 2 in leaves and the assumed absence of re-emission. However, the effectiveness of COS as a GPP tracer depends on understanding the differential responses of COS and CO 2 uptake to environmental factors such as temperature and humidity. Methods We conducted three sets of leaf gas exchange experiments on sunflower leaves. In each experiment, we varied only one environmental factor: COS mole fraction (at two temperatures), humidity, or temperature. During the experiments, COS and CO 2 fluxes were measured, and the data were used to optimize a leaf conductance model. Results We identified the existence of a COS compensation point, which increases with higher temperatures, suggesting potential emissions at higher temperatures when atmospheric COS concentrations are low. Our gas exchange measurements detected a COS compensation point of 58.9 ± 52.4 pmol mol −1 at 20°C and 139.9 ± 26.0 pmol mol −1 at 25°C. As vapor pressure deficit increased and stomatal conductance decreased, we observed that COS leaf uptake decreased more rapidly than CO 2 assimilation. Consequently, the leaf relative uptake ratio (LRU) of COS to CO 2 also decreased when stomatal conductance decreased. The optimized conductance model indicated that the optimum temperature for COS and CO 2 enzymatic uptake was around 35°. However, the maximum net deposition velocity for COS lies between 20 and 25°, due to its temperature-dependent compensation point.

Carbonyl sulfide (COS) is a low abundance atmospheric trace gas that has a tropospheric lifetime of 2–2.5 years, allowing it to reach the stratosphere, where it undergoes photolysis and reactions with ⋅OH and O⋅ radicals, generating precursors of stratospheric aerosols. Vertical profiling of COS has rarely been realised, especially for stratospheric observations. In this study, we introduce a new technique for continuous and discrete vertical profiling of COS based on the analysis of air samples collected by AirCore, the LIghtweight Stratospheric Air (LISA) sampler, and its scaled-up version BigLISA, in three campaigns in Trainou (2019), Kiruna (2021) and Sodankylä (2023) using a Quantum Cascade Laser Spectrometer (QCLS). To eliminate potential COS measurement biases, we have investigated the efficiency of different scrubbers based on cotton and squalene for removing ozone (O₃) and assessed their potential impacts on COS measurement. Furthermore, we examined the influence of different inlet configurations and O₃ scrubbers on the retrieved COS profiles, and found no significant impact within the uncertainties. We found that the differences with the averaged profiles obtained from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) and the measured AirCore profiles and LISA samples were less than 10 % (±50 ppt) at both mid and polar latitudes. Differences between our observations and COS observations from the SPectromètre InfraRouge d'Absorption à Lasers Embarqués (SPIRALE) ranged from 10 % to 15 %, with both methods showing similar COS trends over altitude. Moreover, we found squalene-based scrubbers to be suitable for quantitative O₃ removal. Both AirCore and the LISA samplers are lightweight and suitable for routine balloon-borne COS profiling, providing useful observations for stratospheric research and validation of COS retrievals from remote sensing techniques.

Background Carbonyl Sulfide (COS) is a potential tracer for estimating gross primary productivity (GPP), due to its co-uptake with CO 2 in leaves and the assumed absence of re-emission. However, the effectiveness of COS as a GPP tracer depends on understanding the differential responses of COS and CO 2 uptake to environmental factors such as temperature and humidity. Methods We conducted three sets of leaf gas exchange experiments on sunflower leaves. In each experiment, we varied only one environmental factor: COS mole fraction (at two temperatures), humidity, or temperature. During the experiments, COS and CO 2 fluxes were measured, and the data were used to optimize a leaf conductance model. Results We identified the existence of a COS compensation point, which increases with higher temperatures, suggesting potential emissions at higher temperatures when atmospheric COS concentrations are low. Our gas exchange measurements detected a COS compensation point of 58.9 ± 52.4 pmol mol -1 at 20 °C and 139.9 ± 26.0 pmol mol -1 at 25 °C. As vapor pressure deficit increased and stomatal conductance decreased, we observed that COS leaf uptake decreased more rapidly than CO 2 assimilation. Consequently, the leaf relative uptake ratio (LRU) of COS to CO 2 also decreased when stomatal conductance decreased. The optimized conductance model indicated that the optimum temperature for COS and CO 2 enzymatic uptake was around 35 °. However, the maximum net deposition velocity for COS lies between 20 and 25 °, due to its temperature-dependent compensation point.

Carbonyl sulfide (COS) is a low abundant atmospheric trace gas that has a tropospheric lifetime of 2–2.5 years, allowing it to reach the stratosphere, where it undergoes photolysis and reactions with OH• and O• radicals, generating precursors of stratospheric aerosols. Vertical profiling of COS has rarely been realised, especially for stratospheric observations. In this study, we introduce a new technique for continuous and discrete vertical profiling of COS based on the analysis of air samples collected by AirCore, the LIghtweight Stratospheric Air (LISA) sampler and its scaled-up version BigLISA in three campaigns in Trainou (2019), Kiruna (2021) and Sodankylä (2023) using a Quantum Cascade Laser Spectrometer (QCLS). To eliminate potential COS measurement biases, we have investigated the efficiency of different scrubbers based on cotton and squalene for removing ozone (O₃) and assessed their potential impacts on COS measurement. Furthermore, we examined the influence of different inlet configurations and O₃ scrubbers on the retrieved COS profiles, and found no significant impact within the uncertainties. We found that the differences with the averaged profiles obtained from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) and the measured AirCore profiles at both mid and polar latitudes were less than 5 %, and approximately 10 % for the LISA samples at polar latitudes. Differences between our observations and COS observations from the SPectromètre InfraRouge d’Absorption à Lasers Embarqués (SPIRALE) ranged from 10 % to 15 %, with both methods showing similar COS trends over altitude. Moreover, we found squalene-based scrubbers to be suitable for quantitative O₃ removal. Both AirCore and the LISA samplers are lightweight and suitable for routine balloon-borne COS profiling, providing useful observations for stratospheric research and validation of COS retrievals from remote sensing techniques.

Carbonyl sulfide (COS) is a low abundant atmospheric trace gas that has a tropospheric lifetime of 2–2.5 years, allowing it to reach the stratosphere, where it undergoes photolysis and reactions with OH• and O• radicals, generating precursors of stratospheric aerosols. Vertical profiling of COS has rarely been realised, especially for stratospheric observations. In this study, we introduce a new technique for continuous and discrete vertical profiling of COS based on the analysis of air samples collected by AirCore, the LIghtweight Stratospheric Air (LISA) sampler and its scaled-up version BigLISA in three campaigns in Trainou (2019), Kiruna (2021) and Sodankylä (2023) using a Quantum Cascade Laser Spectrometer (QCLS). To eliminate potential COS measurement biases, we have investigated the efficiency of different scrubbers based on cotton and squalene for removing ozone (O₃) and assessed their potential impacts on COS measurement. Furthermore, we examined the influence of different inlet configurations and O₃ scrubbers on the retrieved COS profiles, and found no significant impact within the uncertainties. We found that the differences with the averaged profiles obtained from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) and the measured AirCore profiles at both mid and polar latitudes were less than 5 %, and approximately 10 % for the LISA samples at polar latitudes. Differences between our observations and COS observations from the SPectromètre InfraRouge d’Absorption à Lasers Embarqués (SPIRALE) ranged from 10 % to 15 %, with both methods showing similar COS trends over altitude. Moreover, we found squalene-based scrubbers to be suitable for quantitative O₃ removal. Both AirCore and the LISA samplers are lightweight and suitable for routine balloon-borne COS profiling, providing useful observations for stratospheric research and validation of COS retrievals from remote sensing techniques.

Many halogenated trace gases are important greenhouse gases and/or contribute to stratospheric ozone depletion, yet their spatial distribution and temporal evolution in the stratosphere remain poorly constrained. We here present a new high-altitude dataset of a large range of these gases. The results are based on a large balloon flight in the Arctic in summer 2021. Air samples were collected using a passive (AirCore) as well as an active (cryogenic) technique; the former being the largest AirCore flown to date, thus enabling the quantification of an expanded variety of halogenated gases. The evaluation of the results demonstrates good comparability in most cases, but also revealed strengths and weaknesses for both sampler types. In addition, we show examples of the scientific value of this data, including the identification of air masses likely originating from the Asian Monsoon region, and the derivation of the average stratospheric transit times (i.e., the mean ages of air) from multiple tracers.

Carbonyl sulfide (COS) is a low abundant atmospheric trace gas that has a tropospheric lifetime of 2–2.5 years, allowing it to reach the stratosphere, where it undergoes photolysis and reactions with OH• and O• radicals, generating precursors of stratospheric aerosols. Vertical profiling of COS has rarely been realised, especially for stratospheric observations. In this study, we introduce a new technique for continuous and discrete vertical profiling of COS based on the analysis of air samples collected by AirCore, the LIghtweight Stratospheric Air (LISA) sampler and its scaled-up version BigLISA in three campaigns in Trainou (2019), Kiruna (2021) and Sodankylä (2023) using a Quantum Cascade Laser Spectrometer (QCLS). To eliminate potential COS measurement biases, we have investigated the efficiency of different scrubbers based on cotton and squalene for removing ozone (O₃) and assessed their potential impacts on COS measurement. Furthermore, we examined the influence of different inlet configurations and O₃ scrubbers on the retrieved COS profiles, and found no significant impact within the uncertainties. We found that the differences with the averaged profiles obtained from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) and the measured AirCore profiles at both mid and polar latitudes were less than 5 %, and approximately 10 % for the LISA samples at polar latitudes. Differences between our observations and COS observations from the SPectromètre InfraRouge d’Absorption à Lasers Embarqués (SPIRALE) ranged from 10 % to 15 %, with both methods showing similar COS trends over altitude. Moreover, we found squalene-based scrubbers to be suitable for quantitative O₃ removal. Both AirCore and the LISA samplers are lightweight and suitable for routine balloon-borne COS profiling, providing useful observations for stratospheric research and validation of COS retrievals from remote sensing techniques.

Carbonyl sulfide (COS) is a low abundant atmospheric trace gas that has a tropospheric lifetime of 2–2.5 years, allowing it to reach the stratosphere, where it undergoes photolysis and reactions with OH• and O• radicals, generating precursors of stratospheric aerosols. Vertical profiling of COS has rarely been realised, especially for stratospheric observations. In this study, we introduce a new technique for continuous and discrete vertical profiling of COS based on the analysis of air samples collected by AirCore, the LIghtweight Stratospheric Air (LISA) sampler and its scaled-up version BigLISA in three campaigns in Trainou (2019), Kiruna (2021) and Sodankylä (2023) using a Quantum Cascade Laser Spectrometer (QCLS). To eliminate potential COS measurement biases, we have investigated the efficiency of different scrubbers based on cotton and squalene for removing ozone (O₃) and assessed their potential impacts on COS measurement. Furthermore, we examined the influence of different inlet configurations and O₃ scrubbers on the retrieved COS profiles, and found no significant impact within the uncertainties. We found that the differences with the averaged profiles obtained from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) and the measured AirCore profiles at both mid and polar latitudes were less than 5 %, and approximately 10 % for the LISA samples at polar latitudes. Differences between our observations and COS observations from the SPectromètre InfraRouge d’Absorption à Lasers Embarqués (SPIRALE) ranged from 10 % to 15 %, with both methods showing similar COS trends over altitude. Moreover, we found squalene-based scrubbers to be suitable for quantitative O₃ removal. Both AirCore and the LISA samplers are lightweight and suitable for routine balloon-borne COS profiling, providing useful observations for stratospheric research and validation of COS retrievals from remote sensing techniques.