Particulate matter (PM) is one major air pollutant that affects human health and the radiation balance of the earth. Thus, it is essential to identify the sources of air pollutants to provide feasible control strategies. In this study, we investigated the size-dependent ¹⁵N and ¹⁸O isotope ratio of N-containing species in aerosols to specify their sources, transport, and formation processes. Aerosol samples of different size ranges were collected using a micro-orifice uniform deposit impactor (MOUDI) on a half-day basis over Xitou Experimental Forest of National Taiwan University (23.40°N, 120.47°E, 1178 m a.s.l.) site at the valley southwest to the central Metropolitan of Taiwan in April 2021. Due to its location and topography, Xitou is downstream of the local circulation, which is dominated by the land-sea breeze and mountain-valley wind and brings the pollutants from the coastal industrial and agricultural activities to the forest during the daytime. Therefore, the samples collected at Xitou are a mixture of complex information. Chemical functional groups measurement was performed using Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) technique beforehand to provide a grasp of the concentration-size distribution for both nitrate and ammonium as a reference to ensure sufficient nitrogen requirement for further isotope analysis at gas chromatography–isotope ratio mass spectrometer (GC-IRMS). The daily average concentration is 3.78±1.82 and 2.47±2.47 ug/m³ for ammonium (NH₄⁺) and nitrate (NO₃^‑), respectively. The concentration during daytime is higher than at nighttime by a factor of 1.3-1.8. The result suggests that pollutants brought by the sea breeze windward contribute to nitrogen-containing aerosols. During a persistent 24-hour weak wind fog event, a significant concentration decreases for both substances (NH₄⁺: 5.34 to 2.12 ug/m³ and NO₃^‑: 4.62 to 0.56 ug/m³) in PM10, likely due to sedimentation. The observed δ¹⁵N in NO₃^‑ increasing with diameter suggests NO₃^‑ at larger particles formed at the upper stream and NO₃^‑ at finer particles formed locally. On the other hand, δ¹⁸O in nitrate shows a similar trend which might be the contribution of RO₂ as the oxidant locally. As NH₄⁺ in aerosols is contributed by ammonia partitioning, δ¹⁵N-NH₄⁺ only reflects the fractionation process during phase change and initial emission. The size-dependent trend of δ¹⁵N-NH₄⁺ shows similar behavior to our previous study in December 2018 and reflects the time points of partitioning. Furthermore, the quantitative analysis of the transport and formation processes based on the size-dependent isotope will be deconvoluted to understand the partitioning of N-containing species in aerosols, which would be necessary for the pollution control strategy and their impact evaluation.

How to cite: Huang, M.-H., Chen, T.-Y., Ren, H., and Hung, H.-M.: The formation and transport of nitrogen-containing species in aerosols over central mountain area of Taiwan using isotope analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6222, https://doi.org/10.5194/egusphere-egu23-6222, 2023.

Natural and engineered nitrogen (N) removal processes in aqueous systems represent important sources of nitrogenous gas emissions, including the potent greenhouse gas nitrous dioxide (N₂O). The relevance of microbial and abiotic formation pathways can be assessed using ¹⁵N tracing techniques. While ¹⁵N-N₂O analysis using optical analyzers is straightforward, quantification of ¹⁵N fractions in inorganic N compounds, ammonium (NH₄⁺), nitrite (NO₂^-), and nitrate (NO₃^-), is typically time-consuming and labor-intensive.

In this study, we developed an automated sample-preparation unit coupled to a membrane-inlet quadrupole mass spectrometer (3n-ASSP-MIMS) for the online quasi-simultaneous analysis of ¹⁵N fractions in NH₄⁺, NO₂^-, and NO₃^-. The technique was designed and validated for applications at moderate (100 - 200 μmol L^-1) to high (2 – 3 mmol L^-1) N, as found in sewer systems, wastewater in treatment plants, or eutrophic surface waters, and ¹⁵N spiking (f₁₅) between 1 and 33%.

The potential of 3n-ASSP-MIMS was demonstrated in a feasibility study, where the technique, in conjunction with ¹⁵N-N₂O analyses by FTIR spectroscopy, was applied to pinpoint nitrifier denitrification as the primary N₂O formation pathway during partial NH₄⁺ oxidation to NO₂^- in a lab-scale sequencing batch reactor.

How to cite: Mohn, J., Huang, K., Eschenbach, W., Wei, J., Hausherr, D., Frey, C., Kupferschmid, A., Dyckmans, J., Joss, A., and Lehmann, M. F.: Tracing N2O production pathways in aqueous ecosystems by quasi-simultaneous online analysis of 15N in reactive nitrogen species and gaseous emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11890, https://doi.org/10.5194/egusphere-egu23-11890, 2023.

Combining measurements, modeling and machine learning to improve N₂O accounting for sustainable agricultural development in sub-Saharan Africa

• Ouma^1,2, E. Harris¹, M. Barthel², J. Six², A. Otinga³, R. Njoroge³, F. Perez-Cruz¹, S. Leitner⁴

¹ Swiss Data Science Centre, ETH Zurich, 8092 Zurich, Switzerland

² Department of Environmental Systems Science, ETH Zurich, Switzerland

³ Department of Soil Science, University of Eldoret, Eldoret, Kenya

⁴ International Institute of Livestock Research (ILRI), Nairobi, Kenya

Sub-Saharan Africa continues to grapple with food insecurity due to low crop yields. While an increase in synthetic fertilisers could potentially increase agricultural productivity in the region, it would lead to an increase in emissions of nitrous oxide (N₂O). Moreover, in this region, the lack of quantification of parameters and documentation of the processes relevant to N₂O emissions have hampered the adoption of climate-smart agricultural practices and advancement of N₂O inventories. This study aims to conduct the first online measurements of N₂O fluxes and isotopic composition from agricultural soils in Uasin Gishu County, Kenya, using the TREX-QCLAS system: quantum cascade laser absorption spectrometer (QCLAS) coupled to a preconcentration unit-TRace gas EXtractor (TREX). The isotopic measurements obtained will be useful in the inference of N₂O production and consumption rates for different pathways and will improve understanding of the key drivers of variability in tropical cropland N₂O fluxes. Further, a collation and analysis of available N₂O flux and isotope data along with campaign measurements and data science approaches will enhance the potential to predict future emissions and promote the development of targeted mitigation strategies.

A pilot phase of initial flux measurements set at the plant research station in Eschikon, Switzerland in early 2023 using the TREX-QCLAS system coupled with automated dynamic chambers optimised for continuous unattended N₂O flux measurements will be conducted before deployment in Kenya. Using clover and grass plots, we aim to understand N₂O fluxes and drivers in a simple system. N₂O measurements will be based on a three-stage calibration protocol (preconcentrated ambient air, preconcentrated compressed air, and calibration of the instrumental concentration dependence using progressive dilution of the anchor standard) followed by measurement of chamber air. Preliminary results of automated quality control and data analysis procedures will be key to ensure success of the instrumental deployment in Kenya in late 2023.

References:

• Harris, E., Diaz-Pines, E., Stoll, E., Schloter, M., Schulz, S., Duffner, C., Li, K., Moore, K. L., Ingrisch, J., Reinthaler, D., Zechmeister-Boltenstern, S., Glatzel, S., Brüggemann, N., & Bahn, M. (2021). Denitrifying pathways dominate nitrous oxide emissions from managed grassland during drought and rewetting. Science advances, 7(6), eabb7118. https://doi.org/10.1126/sciadv.abb7118

• Ibraim, E., Denk, T., Wolf, B., Barthel, M., Gasche, R., Wanek, W., … Mohn, J. (2020). Denitrification is the main nitrous oxide source process in grassland soils according to quasi‐continuous isotopocule analysis and biogeochemical modeling. Global Biogeochemical Cycles, 34(6), e2019GB006505 (19 pp.). https://doi.org/10.1029/2019GB006505

How to cite: Ouma, T.: Combining measurements, modeling and machine learning to improve N2O accounting for sustainable agricultural development in sub-Saharan Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1731, https://doi.org/10.5194/egusphere-egu23-1731, 2023.

Isotopocules of the greenhouse gas nitrous oxide (N₂O), i.e. δ¹⁸O, average δ¹⁵N (δ¹⁵N^bulk), and ¹⁵N site preference (SP) values were used to distinguish between N₂O production pathways in soil. However, as many N₂O production pathways coexist and N₂O can be reduced to N₂, it is not possible to distinguish pathways based only on the natural abundance of N₂O. This applies especially to nitrification and fungal denitrification, where the specific high SP values overlap. Combining ¹⁵N tracer approaches and natural abundance approaches (especially using SP values) could serve to disentangle such pathways, but with the disadvantage that both approaches have to be carried out as parallel experiments.

With this contribution, we present an experimental concept based on the theory, that low level labelling with ¹⁵N of N₂O precursors may allow both, a clear distinction of nitrate or ammonium (NO₃^- or NH₄⁺, respectively) derived N₂O fluxes by ¹⁵N tracing, and the use of SP values of N₂O as additional constraint. This could potentially expand possibilities to evaluate and validate current natural abundance isotopocule mapping approaches.

We will present first results of three experiments to investigate the impact of low labelled precursors on SP values of N₂O produced. Each experiment included treatments with unlabeled and low labelled ¹⁵N precursors to test if low labelling with ¹⁵N affects N₂O isotopocules. In one incubation experiment (i) various levels of ¹⁵N labelling of NO₃^- (between 0.6 and 5 at% ¹⁵N) were used for incubations with Pseudomonas aureofaciens. In another experiment (ii) two pure bacterial (P. aureofaciens and Paracoccus denitrificans) and one pure fungal culture (Fusarium oxysporum) known to be capable of reducing NO₃^- or NO₂^-, respectively, were used. In all experiments, isotopocules of N₂O were unaffected by N₂O reduction as this reduction step could be excluded with selected species. To further investigate isotopocules of N₂O affected by co-occuring processes as well as N₂O reduction a third incubation experiment with two repacked soils was conducted. For this approach, nitrification and/or denitrification was induced by applying NH₄SO₄ and KNO₃ as N₂O precursors, either unlabeled in one treatment or with ¹⁵N labelled KNO₃ (max. 1.1 at% ¹⁵N) in another treatment, both under dry (40% water filled pore space (WFPS)) or wet (80% WFPS) soil conditions.

Based on the results presented, we will be able to give an outlook whether this method can be used to distinguish between nitrification and fungal denitrification.

How to cite: Rohe, L. and Well, R.: Combining low level labelling with 15N and 15N site preference to distinguish N2O production by nitrification and fungal denitrification, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4990, https://doi.org/10.5194/egusphere-egu23-4990, 2023.

The gross primary productivity (GPP), that is the gross uptake of carbon dioxide (CO2) by plants, cannot be measured on ecosystem level but must be inferred by either applying models or measuring proxies. One of those proxies is the trace gas carbonyl sulfide (COS), which is of particular interest, because it shares a very similar pathway into plant leaves as CO2 and is, contrary to the latter, generally not re-emitted.

Due to the need of expensive and sensitive instrumentation, e.g., quantum cascade lasers, only a limited amount of ecosystem measurements and even fewer long-term studies at this scale have been conducted. Consequently, more data focusing on the seasonality and the interannual variability of COS ecosystem fluxes are needed to understand the relationship of the COS to CO2 uptake, i.e., the leaf relative uptake (LRU), for reliable GPP calculations.

To investigate the impact of environmental changes on the LRU we conducted COS, CO2 and H2O eddy covariance flux (EC) measurements at our newly established forest field site in Mieming (Austria) for the last two years. The field site's dominating tree species is Scots pine (Pinus sylvestris) with Juniper trees (Juniper communis) in the understory.
In addition to the EC measurements, we conducted branch chamber measurements within the crown of the Scots pine, two at the treetop and one within the canopy.

Our EC measurements indicate a strong interannual variability of the COS fluxes. While we observed the highest COS uptake in 2021 during May, the COS uptake in 2022 was higher in the period from June to August. We also observed this pattern for the net CO2 fluxes. The fluxes of COS and CO2 concurrently decreased during the winter month and the forest turned into a net source for CO2, while COS was taken up continuously.

The mean LRU across all branch chamber measurements was 1.67 (-) with the chambers within the canopy generally having lower LRUs (1.39 (-)).

How to cite: Spielmann, F. M., Hammerle, A., Scholz, K., and Wohlfahrt, G.: Interannual variability and seasonality of carbonyl sulfide fluxes of an Austrian Scots pine forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10234, https://doi.org/10.5194/egusphere-egu23-10234, 2023.

Flux partitioning, the quantification of photosynthesis and respiration, is a major uncertainty in modelling the carbon cycle and in times when robust models are needed to assess future global changes a persistent problem. A promising new approach is to derive gross primary production (GPP) from measurements of the carbonyl sulfide (COS) flux, the most abundant sulfur-containing trace gas in the atmosphere, with a mean concentration of about 500 pptv in the troposphere. The method is based on the observation that COS and CO2 enter the leaf via a similar pathway and are processed by the same enzyme (carbonic anhydrase), in case of COS a unidirectional process, allowing researchers to use COS uptake as a proxy for the gross CO2 uptake by plants. A prerequisite for using COS as a proxy for photosynthesis is a robust estimation of all non-living-leaf sources and sinks in an ecosystem. One major uncertainty in this regard is the contribution of soils and their respective litter layers to the overall ecosystem COS flux.

COS and CO2 fluxes from litter were measured in real-time using a quantum cascade laser (QCL). The plant litter from four different broadleaf tree species (plane, willow, beech and oak), collected a maximum of one hour before measurements started in the lab (to retain in situ moisture and the microbial biome), was measured under alternating dark and light (UV-A) conditions.

COS litter fluxes varied between the tree species, with plane primarily emitting COS, beech consuming COS and oak and willow being on average neutral (willow with a huge variance). COS litter fluxes within a species seem to correlate with litter moisture. The COS flux was ranging between -4 and 4 pmol kg DW-1 s-1, which is relevant in magnitude compared to the overall ecosystem COS flux and shouldn’t be neglected in future assessments of the global COS budget. 

How to cite: Kitz, F., Wachter, H., and Wohlfahrt, G.: Quantifying the COS fluxes from plane, willow, beach and oak litter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6955, https://doi.org/10.5194/egusphere-egu23-6955, 2023.

Carbonyl sulfide (OCS) is the most dominant sulfur-containing species in the atmosphere and is an important tracer of the terrestrial gross primary productivity as it is involved only in photosynthesis. Biomass burning and terrestrial uptakes by plants and soil is the primary terrestrial source and sink of OCS, respectively.  The Amazon basin alone accounts for 10% of the global biomass burning emission and 33% of the global plant/soil uptake. However, both terms are sensitive to water stress, heat stress, and the associated wildfires in the dry seasons. Here, we estimate the dry-wet seasonal difference of the terrestrial OCS budget over the Amazon region by constraining the NCAR MOZART4 chemistry-transport model with the mid-tropospheric OCS abundances retrieved from NASA’s Thermal Emission Spectrometer (TES) measurements during 2004 and 2012.  Our perturbative calculations show that biomass-burning emissions that are predominant in the south rim of the Amazon have more influence on the mid-tropospheric OCS over the southeast subtropical Amazon. In comparison, the plant/soil uptakes that are predominant in the tropical Amazon have more influence over the northwest tropical Amazon.  This dipole spatial pattern helps distinguish the mid-tropospheric OCS seasonal variability due to biomass-burning emissions and plant/soil uptakes.

How to cite: Tan, L., Li, K.-F., Jiang, X., Kuai, L., and Liang, D.: Satellite-based dry-wet seasonal changes of OCS surface budgets over the Amazon rainforests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1424, https://doi.org/10.5194/egusphere-egu23-1424, 2023.

Carbonyl Sulfide (COS) is the most abundant sulfur-containing gas in the atmosphere, and it is used as a proxy for terrestrial gross primary productivity (GPP). There are uncertainties in the COS fluxes estimations that limit this approach. Oceans are the major source of COS to the atmosphere. In the oceans, the COS is produced by photochemical reactions and "dark production", whose mechanism is not well understood. Hydrolysis is the major process that removes COS from the ocean's surface. Identifying the sulfur isotope values (δ³⁴S) and the isotopic fractionation (e) associated with these major sources and sinks could decrease the uncertainties in the fluxes, based on an improved COS global model with an isotopic mass balance [1]. In the current study, we aim to determine the e  during the hydrolysis process of COS (e_h).  We use a purge and trap system coupled to a GC/MC-ICPMS to measure δ³⁴S values during hydrolysis under different pH, salinity (S), and temperature, representing various oceanic conditions. We calculate from our δ³⁴S and COS concentration measurements a e_h of −2.6 ± 0.3‰ in natural seawater from the Gulf of Aqaba (pH 8.2, 22 , S=41‰). Using an artificial solution at similar pH and temperature conditions (pH 8.0, 22 , S=0.2‰) we found e_h of −2.3 ± 0.2‰, hence, salinity has no significant effect on the fractionation. Using the same artificial solution at 4   we found e_h  of −3.9 ± 0.2‰, thus fractionation increases with decreasing temperatures, as can be expected from theory. We will also report the effect of acidity on e_h from experiments in pH of 4 and 9 (at 22 ). This information on the e_h will help us to understand the contribution of COS hydrolysis to the oceanic source and in the future to establish an isotope mass balance model to decrease the uncertainty of this major source.

[1] Davidson, Chen, Alon Amrani, and Alon Angert. "Tropospheric carbonyl sulfide mass balance based on direct measurements of sulfur isotopes." Proceedings of the National Academy of Sciences 118.6 (2021): e2020060118. 

How to cite: Avidani, Y., Davidson, C., Angert, A., and Amrani, A.: Isotopic fractionation of sulfur during COS hydrolysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6847, https://doi.org/10.5194/egusphere-egu23-6847, 2023.

Methane clumped isotope thermometry relies on accurate measurements of relative abundances of the doubly-substituted isotopologues ¹²CH₂D₂ and ¹³CH₃D. Calibration of the thermometer requires, regardless of the applied technique, i.e., laser absorption spectroscopy or high-resolution mass spectrometry, routine preparation of thermally re-equilibrated samples spanning the temperature and bulk isotopic composition (δ¹³C-, δD-CH₄) range of the target applications.

Here we present a practical method for methane isotopologue re-equilibration over activated γ-Al₂O₃. We demonstrate complete and reproducible re-equilibration of clumped isotope signatures with minimal alteration of the bulk isotope composition, almost complete sample recovery, and no detectable formation of decomposition products. Samples spanning a range in δD-CH₄ of 100 ‰ were equilibrated between 100 °C and 500 °C and used to calibrate a high-resolution quantum cascade laser absorption spectrometer. In addition, we report on a comparison between the spectroscopic measurements carried out at Empa and an independently calibrated high-resolution mass spectrometric technique using a Thermo MAT253 Ultra at IMAU, Utrecht University.

This study is supported by the European Commission under the Horizon 2020 – Research and Innovation Framework Programme, H2020-INFRAIA-2020-1 (grant no. 101008004) and the Swiss National Science Foundation project no. 200021_200977.

How to cite: Prokhorov, I., Tuzson, B., Kueter, N., Sivan, M., Popa, M. E., Röckmann, T., Emmenegger, L., Bernasconi, S. M., and Mohn, J.: Calibration of an optical methane clumped isotope thermometer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-144, https://doi.org/10.5194/egusphere-egu23-144, 2023.

This work demonstrates the analytical basis for an IR (isotope ratio) laser measurement system with the potential to perform routine quantification of biogenic carbon content in liquid fuel products at working refineries. We will present the performance potential for routine quantification for mixtures of C3 and C4 biogenic carbon sources mixed with fossil feedstock.  We will show the progress toward an operational on-line portable monitor. Initial work employed a predilution stage that required challenging transfer techniques to suppress fractionation.  More recent work has explored the potential for the IR based apparatus to directly quantify stable isotopologues that are isobaric in IRMS (isotope ratio mass spectrometry) instruments. The IR system results for ¹³CO₂/¹²CO₂ compare favorably with gold-standard IRMS. 

How to cite: Herndon, S., Nelson, D., Lehmann, S., Heredia-Langner, A., Moran, J., and Bays, J. T.: Tracking Biogenic Carbon in Liquid Fuel Blends using Conventional Mass Spectrometry and Infrared Spectroscopy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6260, https://doi.org/10.5194/egusphere-egu23-6260, 2023.

Sulfate plays a key role in the formation and growth of aerosol particles and cloud droplets in the troposphere and is thus important for air quality and climate. The formation mechanisms of sulfate vary with oxidant levels and environmental conditions and can be partially revealed by its isotopic signatures. Here we measure oxygen (¹⁶O, ¹⁷O, ¹⁸O) and sulfur isotopes (³²S, ³⁴S) of the sulfate aerosol samples collected at coastal Hong Kong, downwind of the highly urbanized Pearl River Delta region. Based on ion measurements, most (95%) of the sulfate collected is non-sea-salt sulfate. The δ³⁴S of sulfate is on average 4.0±2.0 ‰ (range 0.7 – 8.0 ‰), at an average sulfur oxidation ratio of 79±9%. The average oxygen-17 excess (Δ¹⁷O) is -0.1±0.3 ‰, suggesting an important role of OH / transition metals / reactive halogens. The δ¹⁸O of sulfate is on average 4.9±2.1 ‰. The Markov-Chain Monte Carlo model will be used to further constrain sulfate formation mechanisms.

How to cite: Chen, Q., Moon, A., Schauer, A., Wang, T., and Alexander, B.: Sulfate aerosol formation mechanisms constrained by oxygen and sulfur isotopes at coastal Hong Kong, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10454, https://doi.org/10.5194/egusphere-egu23-10454, 2023.

Evaporite salts from saline lakes and playas play active roles in the atmospheric cycles and the climate system, especially in the context of changing climate. Similar processes also occurred on Mars, where large water bodies dried up and formed saline lakes and then salt evaporites and deposits. In this study, various salt samples (brines, lakebed salts, crust salts, playa surface salts, and a series of salts collected at different depths) were collected from two Martian analogue sites (Mang’ai and Dalangtan, MA and DLT) in Qaidam Basin. The salt samples were measured for their ionic compositions and pH as the fundamental characterization, and the effects of sample types and sampling sites are discussed. The hygroscopic properties of solid salts, including crystalized brines, were experimentally determined. The results show strong connections between the ionic composition and hygroscopic properties though discrepancy exists, indicating that the hygroscopicity is sensitive to the molecular forms and the hydrate degrees of salts. Sulfur and chlorine isotopes were measured, and the results are presented as δ³⁴S and δ³⁷Cl. The δ³⁴S values of samples from MA and DLT show great difference. The δ³⁴S values of MA samples are comparable to previously reported fresh water, brines and local precipitation, indicating that the MA samples are strongly influenced by materials exchanged from local environments. The DLT samples have higher δ³⁴S values, which suggest that the material exchanges with surrounding environments are limited. The δ³⁷Cl values are confined within a relatively narrow window compared to literature values. A trend is that the δ³⁷Cl values vary with sample types, i.e., crust > lakebed > brine. This is likely caused by the isotopic fractionation during evaporite precipitation, where the heavier ³⁷Cl isotope is preferably precipitated. The study of salt samples from MA and DLT areas improves the understanding of the active role of evaporite salts in the material cycle and climate system of both Earth and Mars.

Keywords: δ³⁴S, δ³⁷Cl, hygroscopicity, climate, Mars, Qaidam Basin

How to cite: Hao, Y., Qiu, Y., Chen, L., Li, J., Liu, W., Tang, M., Zhang, X., Niu, Z., Pettersson, J., Wang, S., and Kong, X.: Isotopic and chemical characterization of saline lake and playa salts: Implication for climate on Earth and Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14497, https://doi.org/10.5194/egusphere-egu23-14497, 2023.