Identification and quantification of sources and sinks of carbonyl sulfide

2021 ◽  
Author(s):  
Alessandro Zanchetta ◽  
Linda M.J. Kooijmans ◽  
Steven van Heuven ◽  
Andrea Scifo ◽  
Bert Scheeren ◽  
...  
Keyword(s):  
Gross Primary Production ◽  
Carbonyl Sulfide ◽  
Terrestrial Ecosystems ◽  
Lagrangian Model ◽  
Atmospheric Measurements ◽  
Model Framework ◽  
Sources And Sinks ◽  
Quantum Cascade ◽  
Production Facilities

<p>Carbonyl sulfide (COS) is the most abundant reduced sulfur gas in the atmosphere and is used as a tracer for gross primary production (GPP) of terrestrial ecosystems and stomatal conductance of leaves. At present, its usefulness is limited by the uncertainties in the estimation of its sources and sinks. In this study, we aim to understand the COS budget using atmospheric COS enhancements at the Lutjewad tower (53°24’N, 6°21’E, 1m a.s.l.) and atmospheric measurements of COS in the province of Groningen using a mobile van. We infer the sources and sinks of COS using continuous in situ mole fraction profile measurements of COS at Lutjewad. We determined the nighttime COS fluxes to be -3.0 ± 2.6 pmol m<sup>-2</sup> s<sup>-1</sup> using the radon-tracer correlation approach. We observed enhancements of COS mole fractions on the order of 100 ppt (lasting a few days) to 1000 ppt (lasting a few hours) at three occasions. To quantify potentially unidentified COS sources, we have made additional measurements by collecting air flasks that were analyzed later in the laboratory and with a continuous quantum cascade laser spectrometer. We have identified multiple COS sources, such as biodigesters, sugar production facilities and silicon carbide production facilities. Furthermore, we simulate the Lutjewad COS mole fractions in a Lagrangian model framework to quantitatively understand the COS sources and sinks. These results are useful for improving our understanding of the sources and sinks of COS, contributing to the use of COS as a tracer for GPP.</p>

scholarly journals Continuous and high-precision atmospheric concentration measurements of COS, CO<sub>2</sub>, CO and H<sub>2</sub>O using a quantum cascade laser spectrometer (QCLS)

2016 ◽  
Vol 9 (11) ◽  
pp. 5293-5314 ◽  
Author(s):  
Linda M. J. Kooijmans ◽  
Nelly A. M. Uitslag ◽  
Mark S. Zahniser ◽  
David D. Nelson ◽  
Stephen A. Montzka ◽  
...  
Keyword(s):  
Spectral Line ◽  
Absorption Line ◽  
High Precision ◽  
Quantum Cascade Laser ◽  
Gross Primary Production ◽  
Laser Spectrometer ◽  
Atmospheric Measurements ◽  
Atmospheric Concentration ◽  
Quantum Cascade

Abstract. Carbonyl sulfide (COS) has been suggested as a useful tracer for gross primary production as it is taken up by plants in a similar way as CO2. To explore and verify the application of this novel tracer, it is highly desired to develop the ability to perform continuous and high-precision in situ atmospheric measurements of COS and CO2. In this study we have tested a quantum cascade laser spectrometer (QCLS) for its suitability to obtain accurate and high-precision measurements of COS and CO2. The instrument is capable of simultaneously measuring COS, CO2, CO and H2O after including a weak CO absorption line in the extended wavelength range. An optimal background and calibration strategy was developed based on laboratory tests to ensure accurate field measurements. We have derived water vapor correction factors based on a set of laboratory experiments and found that for COS the interference associated with a water absorption line can dominate over the effect of dilution. This interference can be solved mathematically by fitting the COS spectral line separately from the H2O spectral line. Furthermore, we improved the temperature stability of the QCLS by isolating it in an enclosed box and actively cooling its electronics with the same thermoelectric chiller used to cool the laser. The QCLS was deployed at the Lutjewad atmospheric monitoring station (60 m; 6°21′ E, 53°24′ N; 1 m a.s.l.) in the Netherlands from July 2014 to April 2015. The QCLS measurements of independent working standards while deployed in the field showed a mean difference with the assigned cylinder value within 3.3 ppt COS, 0.05 ppm for CO2 and 1.7 ppb for CO over a period of 35 days. The different contributions to uncertainty in measurements of COS, CO2 and CO were summarized and the overall uncertainty was determined to be 7.5 ppt for COS, 0.23 ppm for CO2 and 3.3 ppb for CO for 1-minute data. A comparison of in situ QCLS measurements with those from concurrently filled flasks that were subsequently measured by the QCLS showed a difference of −9.7 ± 4.6 ppt for COS. Comparison of the QCLS with a cavity ring-down spectrometer showed a difference of 0.12 ± 0.77 ppm for CO2 and −0.9 ± 3.8 ppb for CO.

scholarly journals Continuous and high precision atmospheric concentration measurements of COS, CO<sub>2</sub>, CO and H<sub>2</sub>O using a quantum cascade laser spectrometer (QCLS)

2016 ◽  
Author(s):  
Linda M. J. Kooijmans ◽  
Nelly A. M. Uitslag ◽  
Mark S. Zahniser ◽  
David D. Nelson ◽  
Stephen A. Montzka ◽  
...  
Keyword(s):  
Spectral Line ◽  
High Precision ◽  
Quantum Cascade Laser ◽  
Gross Primary Production ◽  
Temperature Stability ◽  
Laser Spectrometer ◽  
Atmospheric Measurements ◽  
Atmospheric Concentration ◽  
Quantum Cascade

Abstract. Carbonyl sulfide (COS) has been suggested as a useful tracer for Gross Primary Production as it is taken up by plants in a similar way as CO2. To explore and verify the application of this novel tracer, it is highly desired to develop the ability to perform continuous and high precision in situ atmospheric measurements of COS and CO2. In this study we have tested a quantum cascade laser spectrometer (QCLS) for its suitability to obtain accurate and high precision measurements of COS and CO2. The instrument is capable of simultaneously measuring COS, CO2, CO, and H2O after including a weak CO absorption line in the extended wavelength range. An optimal background and calibration strategy was developed based on laboratory tests to ensure accurate field measurements. We have derived water vapor correction factors based on a set of laboratory experiments, and found that line interference with H2O dominates over the dilution effect for COS. This interference can be solved mathematically by fitting the COS spectral line separately from the H2O spectral line. Furthermore, we improved the temperature stability of the QCLS by isolating it in an enclosed box and actively cooling its electronics with the same thermoelectric chiller used to cool the laser. The QCLS was deployed at the Lutjewad atmospheric monitoring station (60 m, 6°21'E, 53°24'N, 1 m a.s.l.) in the Netherlands from July 2014 to April 2015. The measurements of an independent calibration standard showed a mean difference with the assigned cylinder value within 3.3 ppt COS, 0.05 ppm for CO2 and 1.7 ppb for CO over a period of 35 days. The different contributions to uncertainty in measurements of COS, CO2 and CO were summarized and the overall uncertainty was determined to be 7.1 ppt for COS, 0.22 ppm for CO2 and 3.4 ppb for CO for one second data. The comparison of in situ QCLS measurements with measurements from flasks and a cavity ring-down spectrometer showed a difference of −3.5 ± 8.6 ppt for COS, 0.12 ± 0.77 ppm for CO2 and −0.9 ± 3.8 ppb for CO.

scholarly journals A new model of the global biogeochemical cycle of carbonyl sulfide – Part 2: Use of ocs to constrain gross primary productivity of current vegetation models

2014 ◽  
Vol 14 (20) ◽  
pp. 27663-27729 ◽  
Author(s):  
T. Launois ◽  
P. Peylin ◽  
S. Belviso ◽  
B. Poulter
Keyword(s):  
Northern Hemisphere ◽  
Seasonal Variations ◽  
Gross Primary Production ◽  
Experimental Studies ◽  
Carbonyl Sulfide ◽  
Surface Fluxes ◽  
Atmospheric Measurements ◽  
Mixing Ratios ◽  
Co2 Diffusion ◽  
Vegetation Models

Abstract. Clear analogies between carbonyl sulfide (OCS) and carbon dioxide (CO2) diffusion pathways through leaves have been revealed by experimental studies with plant uptake playing an important role for the atmospheric budget of both species. Here we use atmospheric OCS to evaluate the gross primary production (GPP) of three dynamic global vegetation models (LPJ, NCAR-CLM4 and ORCHIDEE). Vegetation uptake of OCS is modeled as a linear function of GPP and LRU, the ratio of OCS to CO2 deposition velocities to plants. New parameterizations for the non-photosynthetic sinks (oxic soils, atmospheric oxidation) and biogenic sources (oceans and anoxic soils) of OCS are also provided. Despite new large oceanic emissions, global OCS budgets created with each vegetation model show exceeding sinks by several hundreds of Gg S yr−1. An inversion of the surface fluxes (optimization of a global scalar which accounts for flux uncertainties) led to balanced OCS global budgets, as atmospheric measurements suggest, mainly by drastic reduction (−30%) of soil and vegetation uptakes. The amplitude of variations in atmospheric OCS mixing ratios is mainly dictated by the vegetation sink over the Northern Hemisphere. This allows for bias recognition in the GPP representations of the three selected models. Main bias patterns are (i) the terrestrial GPP of ORCHIDEE at high Northern latitudes is currently over-estimated, (ii) the seasonal variations of the GPP are out of phase in the NCAR-CLM4 model, showing a maximum carbon uptake too early in spring in the northernmost ecosystems, (iii) the overall amplitude of the seasonal variations of GPP in NCAR-CLM4 is too small, and (iv) for the LPJ model, the GPP is slightly out of phase for northernmost ecosystems and the respiration fluxes might be too large in summer in the Northern Hemisphere.

Study on Stratospheric Carbonyl Sulfide Transport and Chemistry using ‘Age of Air’

2021 ◽  
Author(s):  
Chenxi Qiu ◽  
Felix Ploeger ◽  
Jens-Uwe Grooß ◽  
Marc von Hobe
Keyword(s):  
Atmospheric Chemistry ◽  
Michelson Interferometer ◽  
Carbonyl Sulfide ◽  
Polar Vortex ◽  
Lagrangian Model ◽  
Latitude Range ◽  
Mixing Ratios ◽  
Enhanced Absorption ◽  
In Situ Data

&lt;p&gt;Carbonyl sulfide (OCS or COS) is the longest lived and the most abundant reduced sulfur gas in the atmosphere. As chemical loss of OCS in the troposphere is slow, it can reach the stratosphere, where it is &amp;#160;photochemically oxidized and converted to stratospheric sulfate aerosol, being the largest source thereof in times of volcanic quiescence. Chemistry transport models show that OCS conversion occurs mainly in the &amp;#8216;tropical pipe&amp;#8217; region, while along the lower branch of Brewer-Dobson circulation (BDC), OCS is passively transported without significant chemical loss. The OCS depleted air is transported along the upper branch of BDC and descends again at high latitudes. Using the distinct characteristics of &amp;#160;&amp;#8216;age of air&amp;#8217; in the upper and lower branches of the BDC, this picture of OCS transport and especially the role of the &amp;#8216;tropical pipe&amp;#8217; as the main region of OCS conversion can be supported by looking at the relationship between age spectra and OCS mixing ratios.&lt;/p&gt;&lt;p&gt;In this study, we will investigate the relation of OCS mixing ratios and mean age of air as well as mass fractions of air with different transit times using satellite-based measurements from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and ACE-FTS (Atmospheric Chemistry Experiment - infrared Fourier Transform Spectrometer), and age spectra of air from CLaMS (Chemical Lagrangian Model of the Stratosphere).&lt;/p&gt;&lt;p&gt;In addition to satellite data analysis, we will investigate the distribution of OCS in the UTLS (upper troposphere and lower stratosphere) region and its relation to the age spectra using high-resolution in-situ observations of OCS. This unique dataset was obtained during the SOUTHTRAC mission in autumn 2019 by AMICA (Airborne Mid-Infrared Cavity enhanced Absorption spectrometer) on board the HALO (High Altitude Long Range) research aircraft. Flights from the main &amp;#160;campaign base in R&amp;#237;o Grande, Argentina (53.8S, 67.7W) covered a wide latitude range from 48&amp;#176; N to 70&amp;#176; S, even reaching the southern polar vortex where aged air masses having descended from high altitudes are typically found.&lt;/p&gt;&lt;p&gt;Our analysis of both satellite and in-situ data generally supports the established picture of OCS conversion in the &amp;#8216;tropical pipe&amp;#8217;.&lt;/p&gt;

scholarly journals A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide

Sensors ◽  
2018 ◽  
Vol 18 (7) ◽  
pp. 2380 ◽  
Author(s):  
Silvia Viciani ◽  
Alessio Montori ◽  
Antonio Chiarugi ◽  
Francesco D’Amato
Keyword(s):  
Carbon Monoxide ◽  
Quantum Cascade Laser ◽  
Climate Models ◽  
Trace Gas ◽  
Laser Spectrometer ◽  
Atmospheric Measurements ◽  
Gas Concentration ◽  
Quantum Cascade ◽  
Measurement Campaigns

Trace gas concentration measurements in the stratosphere and troposphere are critically required as inputs to constrain climate models. For this purpose, measurement campaigns on stratospheric aircraft and balloons are being carried out all over the world, each one involving sensors which are tailored for the specific gas and environmental conditions. This paper describes an automated, portable, mid-infrared quantum cascade laser spectrometer, for in situ carbon monoxide mixing ratio measurements in the stratosphere and troposphere. The instrument was designed to be versatile, suitable for easy installation on different platforms and capable of operating completely unattended, without the presence of an operator, not only during one flight but for the whole period of a campaign. The spectrometer features a small size (80 × 25 × 41 cm3), light weight (23 kg) and low power consumption (85 W typical), without being pressurized and without the need of calibration on the ground or during in-flight operation. The device was tested in the laboratory and in-field during a research campaign carried out in Nepal in summer 2017, onboard the stratospheric aircraft M55 Geophysica. The instrument worked extremely well, without external maintenance during all flights, proving an in-flight sensitivity of 1–2 ppbV with a time resolution of 1 s.

scholarly journals Eddy covariance carbonyl sulfide flux measurements with a quantum cascade laser absorption spectrometer

2017 ◽  
Vol 10 (9) ◽  
pp. 3525-3537 ◽  
Author(s):  
Katharina Gerdel ◽  
Felix Maximilian Spielmann ◽  
Albin Hammerle ◽  
Georg Wohlfahrt
Keyword(s):  
Eddy Covariance ◽  
Quantum Cascade Laser ◽  
Gross Primary Production ◽  
Carbonyl Sulfide ◽  
Linear Interpolation ◽  
Trace Gas ◽  
Quantum Cascade ◽  
Laser Absorption ◽  
Flux Measurements ◽  
High Pass

Abstract. The trace gas carbonyl sulfide (COS) has lately received growing interest from the eddy covariance (EC) community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers, QCLAS), a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to present a detailed characterisation of the COS measurement with the Aerodyne QCLAS in the context of the EC technique and to recommend best EC processing practices for those measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed the occurrence of sensor drift under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering) as opposed to block averaging and linear interpolation of regular background measurements for covariance computation. Experimental low-pass filtering correction factors were derived from a detailed cospectral analysis. The CO2 and H2O flux measurements obtained with the QCLAS were compared with those obtained with a closed-path infrared gas analyser. Overall, our results suggest small, but systematic differences between the various high-pass filtering scenarios with regard to the fraction of data retained in the quality control and flux magnitudes. When COS and CO2 fluxes are combined in the ecosystem relative uptake rate, systematic differences between the high-pass filtering scenarios largely cancel out, suggesting that this relative metric represents a robust key parameter comparable between studies relying on different post-processing schemes.

Inverse modelling of Carbonyl Sulfide (COS): towards nonlinear model and satellite data assimilation

2021 ◽  
Author(s):  
Jin Ma ◽  
Linda M.J Kooijmans ◽  
Ara Cho ◽  
Stephen A. Montzka ◽  
Norbert Glatthor ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Satellite Data ◽  
Transport Model ◽  
Gross Primary Production ◽  
Current Model ◽  
Carbonyl Sulfide ◽  
Linear Inversion ◽  
Sources And Sinks ◽  
First Order ◽  
The Tropics

&lt;p&gt;Atmospheric Carbonyl Sulfide (COS) is a useful tracer for assessing gross primary production (GPP). COS is also an important contributor to stratospheric sulfate aerosols (SSA) which cool the climate. However, the global budget of COS remains unresolved due to insufficient observations. We implemented a linear inversion framework within the TM5-4DVAR global chemistry transport model constrained by NOAA surface network to investigate the sources and sinks of COS (Ma et al., 2020). To close the gap between sources and sinks, we focused on inversions that optimize what is thought to be a &amp;#8220;missing&amp;#8221; source amounting to 432 GgS a&lt;sup&gt;-1&lt;/sup&gt;. We found that a tropical missing source was likely, which could either be an indication of an underestimated ocean source, or overestimated biosphere uptake. Additionally, we found the biosphere uptake to be underestimated at higher latitudes of the Northern Hemisphere. Inversions were validated with HIPPO aircraft data, NOAA airborne profiles and satellite data (MIPAS, TES and ACE-FTS), indicating an underestimation of COS in troposphere. We further implemented a first-order dependency of COS biosphere flux on COS mole fractions in the atmosphere boundary layer, which renders the inversions nonlinear. As expected based on the known drawdown of COS by biosphere uptake, it is found that the dependence of the biosphere flux on COS mole fractions reduced the budget gap by 137 GgS a&lt;sup&gt;-1&lt;/sup&gt;. We further optimized COS fluxes separately over ocean and land, accounting for the first-order dependency of biosphere uptake on COS mole fractions. These results suggest that the missing COS sources may originate from the ocean (207 GgS a&lt;sup&gt;-1&lt;/sup&gt;), despite recent work in which the ocean is explicitly studied suggesting otherwise.&amp;#160; Understanding this apparent discrepancy will be an important topic to elucidate. In the future, we plan to take the advantage of available satellite data products to better constrain the COS flux budget in the tropics. COS products from the MIPAS and TES satellites are good candidates for data assimilation in the current model.&lt;/p&gt;

scholarly journals A new model of the global biogeochemical cycle of carbonyl sulfide – Part 2: Use of carbonyl sulfide to constrain gross primary productivity in current vegetation models

2015 ◽  
Vol 15 (16) ◽  
pp. 9285-9312 ◽  
Author(s):  
T. Launois ◽  
P. Peylin ◽  
S. Belviso ◽  
B. Poulter
Keyword(s):  
Northern Hemisphere ◽  
Seasonal Variations ◽  
Gross Primary Production ◽  
Regional Scale ◽  
Carbonyl Sulfide ◽  
Atmospheric Measurements ◽  
Modeling Framework ◽  
Varying Coefficients ◽  
Community Land Model ◽  
Vegetation Models

Abstract. Clear analogies between carbonyl sulfide (OCS) and carbon dioxide (CO2) diffusion pathways through leaves have been revealed by experimental studies, with plant uptake playing an important role for the atmospheric budget of both species. Here we use atmospheric OCS to evaluate the gross primary production (GPP) of three dynamic global vegetation models (Lund–Potsdam–Jena, LPJ; National Center for Atmospheric Research – Community Land Model 4, NCAR-CLM4; and Organising Carbon and Hydrology In Dynamic Ecosystems, ORCHIDEE). Vegetation uptake of OCS is modeled as a linear function of GPP and leaf relative uptake (LRU), the ratio of OCS to CO2 deposition velocities of plants. New parameterizations for the non-photosynthetic sinks (oxic soils, atmospheric oxidation) and biogenic sources (oceans and anoxic soils) of OCS are also provided. Despite new large oceanic emissions, global OCS budgets created with each vegetation model show exceeding sinks by several hundred Gg S yr−1. An inversion of the surface fluxes (optimization of a global scalar which accounts for flux uncertainties) led to balanced OCS global budgets, as atmospheric measurements suggest, mainly by drastic reduction (up to −50 %) in soil and vegetation uptakes. The amplitude of variations in atmospheric OCS mixing ratios is mainly dictated by the vegetation sink over the Northern Hemisphere. This allows for bias recognition in the GPP representations of the three selected models. The main bias patterns are (i) the terrestrial GPP of ORCHIDEE at high northern latitudes is currently overestimated, (ii) the seasonal variations of the GPP are out of phase in the NCAR-CLM4 model, showing a maximum carbon uptake too early in spring in the northernmost ecosystems, (iii) the overall amplitude of the seasonal variations of GPP in NCAR-CLM4 is too small, and (iv) for the LPJ model, the GPP is slightly out of phase for the northernmost ecosystems and the respiration fluxes might be too large in summer in the Northern Hemisphere. These results rely on the robustness of the OCS modeling framework and, in particular, the choice of the LRU values (assumed constant in time) and the parameterization of soil OCS uptake with small seasonal variations. Refined optimization with regional-scale and seasonally varying coefficients might help to test some of these hypothesis.

scholarly journals Tropospheric carbonyl sulfide mass balance based on direct measurements of sulfur isotopes

2021 ◽  
Vol 118 (6) ◽  
pp. e2020060118
Author(s):  
Chen Davidson ◽  
Alon Amrani ◽  
Alon Angert
Keyword(s):  
Mass Balance ◽  
Plant Uptake ◽  
Sulfur Isotopes ◽  
Gross Primary Production ◽  
Carbonyl Sulfide ◽  
Relative Magnitude ◽  
Anthropogenic Source ◽  
Sources And Sinks ◽  
Relative Contribution ◽  
Marine Source

Robust estimates for the rates and trends in terrestrial gross primary production (GPP; plant CO2 uptake) are needed. Carbonyl sulfide (COS) is the major long-lived sulfur-bearing gas in the atmosphere and a promising proxy for GPP. Large uncertainties in estimating the relative magnitude of the COS sources and sinks limit this approach. Sulfur isotope measurements (34S/32S; δ34S) have been suggested as a useful tool to constrain COS sources. Yet such measurements are currently scarce for the atmosphere and absent for the marine source and the plant sink, which are two main fluxes. Here we present sulfur isotopes measurements of marine and atmospheric COS, and of plant-uptake fractionation experiments. These measurements resulted in a complete data-based tropospheric COS isotopic mass balance, which allows improved partition of the sources. We found an isotopic (δ34S ± SE) value of 13.9 ± 0.1‰ for the troposphere, with an isotopic seasonal cycle driven by plant uptake. This seasonality agrees with a fractionation of −1.9 ± 0.3‰ which we measured in plant-chamber experiments. Air samples with strong anthropogenic influence indicated an anthropogenic COS isotopic value of 8 ± 1‰. Samples of seawater-equilibrated-air indicate that the marine COS source has an isotopic value of 14.7 ± 1‰. Using our data-based mass balance, we constrained the relative contribution of the two main tropospheric COS sources resulting in 40 ± 17% for the anthropogenic source and 60 ± 20% for the oceanic source. This constraint is important for a better understanding of the global COS budget and its improved use for GPP determination.

scholarly journals Tropospheric carbonyl sulfide mass-balance based on direct measurements of sulfur isotopes

2020 ◽  
Author(s):  
Chen Davidson ◽  
Alon Amrani ◽  
Alon Angert
Keyword(s):  
Mass Balance ◽  
Sulfur Isotopes ◽  
Gross Primary Production ◽  
Carbonyl Sulfide ◽  
Relative Magnitude ◽  
Anthropogenic Source ◽  
Sources And Sinks ◽  
Relative Contribution ◽  
Direct Measurements ◽  
Isotopic Signal

Abstract Carbonyl sulfide (COS) is the major long-lived sulfur bearing gas in the atmosphere and a promising proxy for terrestrial gross primary production (GPP; CO2 uptake). However, large uncertainties in estimating the relative magnitude of the COS sources and sinks limit this approach. Isotopic measurements have been suggested as a novel tool to constrain COS sources, yet such measurements are currently scarce. Here we present, for the first time, a complete data-based tropospheric COS isotopic mass balance, which allows improved partition of the sources. We found an isotopic (δ34S±SE) value of 13.9±0.1‰ (versus V-CDT standard) for the troposphere, with an isotopic seasonal cycle driven by plant uptake. This seasonality agrees with a fractionation of -1.9±0.3‰ which we measured in plant-chamber experiments. Anthropogenic-influenced air samples indicated an anthropogenic COS isotopic signal of 8±1‰. Samples of seawater-equilibrated-air indicate that marine COS emissions have an isotopic signal of 13±0.4‰. Using our new data-based mass balance, we constrained the relative contribution of the two main tropospheric COS sources resulting in 26±11% for the anthropogenic source and 74±23% for the oceanic source. This constraint is important for a better understanding of the global COS budget and its improved use for GPP determination.

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