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1. Variability and Controls of p CO ₂ and Air‐Water CO ₂ Fluxes in a Temperate River

   https://doi.org/10.1029/2024JG008434  

   Young, Fischer_L; Colman, Benjamin_P; Carter, Alice_M; Fiejó_de_Lima, Rafael; Shangguan, Qipei; Payn, Robert_A; DeGrandpre, Michael_D (February 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract Measurements of riverine dissolved inorganic carbon, total alkalinity (A_T), pH, and the partial pressure of carbon dioxide (pCO₂) can provide insights into the biogeochemical function of rivers, including the processes that control biological production, chemical speciation, and air‐water CO₂fluxes. The complexity created by these combined processes dictates that studies of inorganic carbon be made over broad spatial and temporal scales. Time‐series data like these are relatively rare, however, because sampling and measurements are labor intensive and, for some variables, good measurement quality is difficult to achieve (e.g., pH). In this study, spectrophotometric pH and A_Twere quantified with high precision and accuracy at biweekly to monthly intervals over a four‐year period (2018–2021) along 216 km of the Upper Clark Fork River (UCFR) in the northern Rocky Mountains, USA. We use these and other time‐series data to provide insights into the processes that control river inorganic carbon, with a focus onpCO₂and air‐water CO₂fluxes. We found that seasonal snowmelt runoff increasedpCO₂and that expected increase and decrease ofpCO₂due to seasonal heating and cooling were likely offset by an increase and loss of algal biomass, respectively. Overall, the UCFR was a small net source (0.08 ± 0.14 mol m⁻² d⁻¹) of CO₂to the atmosphere over the four‐year study period with highly variable annual averages (0.0–0.10 mol m⁻² d⁻¹). The seasonally correlated, offsetting mechanisms highlight the challenges in predictingpCO₂and air‐water CO₂fluxes in rivers. 

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2. Capturing CO ₂ in Quadrupolar Binding Pockets: Broadband Microwave Spectroscopy of Pyrimidine-(CO ₂ ) _n , n = 1,2

   https://doi.org/10.1021/acs.jpca.3c07930  

   Welsh, Blair A; Urbina, Andres S; Ho, Tuan A; Rempe, Susan L; Slipchenko, Lyudmila V; Zwier, Timothy S (February 2024, The Journal of Physical Chemistry A)
3. Cobalt-Group 13 Complexes Catalyze CO ₂ Hydrogenation via a Co(−I)/Co(I) Redox Cycle

   https://doi.org/10.1021/acscatal.9b03534  

   Vollmer, Matthew V.; Ye, Jingyun; Linehan, John C.; Graziano, Brendan J.; Preston, Andrew; Wiedner, Eric S.; Lu, Connie C. (January 2020, ACS Catalysis)
4. Elucidating the active sites for CO ₂ electroreduction on ligand-protected Au ₂₅ nanoclusters

   https://doi.org/10.1039/c8cy01099d  

   Austin, Natalie; Zhao, Shuo; McKone, James R.; Jin, Rongchao; Mpourmpakis, Giannis (January 2018, Catalysis Science & Technology)

   Using density functional theory (DFT) calculations, we investigated the electrochemical reduction of CO 2 and the competing H 2 evolution reaction on ligand-protected Au 25 nanoclusters (NCs) of different charge states, Au 25 (SR) 18 q ( q = −1, 0, +1). Our results showed that regardless of charge state, CO 2 electroreduction over Au 25 (SR) 18 q NCs was not feasible because of the extreme endothermicity to stabilize the carboxyl (COOH) intermediate. When we accounted for the removal of a ligand (both –SR and –R) from Au 25 (SR) 18 q under electrochemical conditions, surprisingly we found that this is a thermodynamically feasible process at the experimentally applied potentials with the generated surface sites becoming active centers for electrocatalysis. In every case, the negatively charged NCs, losing a ligand from their surface during electrochemical conditions, were found to significantly stabilize the COOH intermediate, resulting in dramatically enhanced CO 2 reduction. The generated sites for CO 2 reduction were also found to be active for H 2 evolution, which agrees with experimental observations that these two processes compete. Interestingly, we found that the removal of an –R ligand from the negatively charged NC, resulted in a catalyst that was both active and selective for CO 2 reduction. This work highlights the importance of both the overall charge state and generation of catalytically active surface sites on ligand-protected NCs, while elucidating the CO 2 electroreduction mechanisms. Overall, our work rationalizes a series of experimental observations and demonstrates pathways to convert a very stable and catalytically inactive NC to an active electrocatalyst. 

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5. The Importance of Contemporaneous Wind and p CO ₂ Measurements for Regional Air‐Sea CO ₂ Flux Estimates

   https://doi.org/10.1029/2023JC020744  

   Nickford, S; Palter, J B; Mu, L (June 2024, Journal of Geophysical Research: Oceans)

   Abstract Few observational platforms are able to sustain direct measurements of all the key variables needed in the bulk calculation of air‐sea carbon dioxide (CO₂) exchange, a capability newly established for some Uncrewed Surface Vehicles (USVs). Western boundary currents are particularly challenging observational regions due to strong variability and dangerous sea states but are also known hot spots for CO₂uptake, making air‐sea exchange quantification in this region both difficult and important. Here, we present new observations collected by Saildrone USVs in the Gulf Stream during the winters of 2019 and 2022. We compared Saildrone data across co‐located vehicles and against the Pioneer Array moorings to validate the data quality. We explored how CO₂flux estimates differ when all variables needed to calculate fluxes from the bulk formulas are simultaneously measured on the same platform, relative to the situation where in situ observations must be combined with publicly‐available data products. We systematically replaced variables in the bulk formula with those often used for local and regional flux estimates. The analysis revealed that when using the ERA‐5 reanalysis wind speed in place of in situ observations, the ocean uptake of CO₂is underestimated by 8%; this underestimate grows to 9% if the NOAA Marine Boundary Layer atmospheric CO₂product and ERA‐5 significant wave height are also used in place of in situ observations. Overall our findings point to the importance of collecting contemporaneous observations of wind speed and oceanpCO₂to reduce biases in estimates of regional CO₂flux, especially during high wind events. 

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