Band Of Carbon Monoxide Research Articles

Changing CO bands in near-IR spectra of CP Cephei

ABSTRACT We present time-series near-infrared spectra for the classical Cepheid, CP Cephei, from the Astrophysical Research Consortium 3.5-m telescope and near-infrared spectrograph, TripleSpec, at Apache Point Observatory, NM, USA. Spectral observations were made at nine points through the minimum and partway up the ascending portion of the optical light curve for the star. Carbon monoxide (CO) was detected in absorption in the 2.3-$\mu$m region for each observation. We measured the strength of CO absorption using the 2-0 band head in the feature for each observation and confirm that the CO varies with pulsation. We show that these measurements follow the $(J-K)$ colour curve, confirming that temperature drives the destruction of CO. By obtaining convolved filter magnitudes from the spectral data we found that the effect of the CO feature on K magnitudes is small, unlike the CO feature in the mid-infrared at 4.5 $\mu$m. The dissociation of CO in the near-infrared spectra tracks with the effect seen in the mid-infrared photometric measurements of a similar Galactic Cepheid. Confirmation of the varying CO feature illustrates the need for further investigations into the related mid-infrared period–colour–metallicity relation in order to address the impact of Cepheid metallicities on the Hubble tension.

Carbon monoxide cooling in radiative transfer modelling of supernovae

ABSTRACT Carbon monoxide (CO) emission has been observed in a number of core-collapse supernovae (SNe) and is known to be an important coolant at late times. We have implemented a chemical reaction network in the radiative-transfer code cmfgen to investigate the formation of CO and its impact on SN ejecta. We calculate two 1D SN models with and without CO: a BSG explosion model at one nebular epoch and a full time-sequence (50–300 d) for a red supergiant explosion. In both models, CO forms at nebular times in the dense, inner regions at velocities <2000 km s$^{-1}$ where line emission from CO can dominate the cooling and reduce the local temperature by as much as a factor of 2, weakening emission lines and causing the optical light curve to fade faster. That energy is instead emitted in CO bands, primarily the fundamental band at $\sim 4.5 \mathrm{\mu m}$, which accounts for up to 20 per cent of the total luminosity at late times. However, the non-monotonic nature of the CO cooling function can cause numerical difficulties and introduce multiple temperature solutions. This issue is compounded by the sensitivity of the CO abundance to a few reaction rates, many of which have large uncertainties or disparate values across literature sources. Our results also suggest that, in many SNe, CO-level populations are far from their local thermodynamic equilibrium values. Unfortunately, accurate collisional data, necessary to compute non-local thermodynamic equilibrium populations, are limited to a few transitions.

High-temperature line strengths with He- and Ar-broadening coefficients of the P(20) line in the 1 $$\leftarrow$$ 0 band of carbon monoxide

High-temperature line strengths with He- and Ar-broadening coefficients of the P(20) line in the 1 $$\leftarrow$$ 0 band of carbon monoxide

Measurement and calculation of CO (7-0) overtone line intensities.

Intensities of 14 lines in the sixth overtone (7-0) band of carbon monoxide (12C16O) are measured in the visible range between 14300 and 14500 cm-1 using a frequency-stabilized cavity ring-down spectrometer. This is the first observation of such a high and weak overtone spectrum of the CO molecule. A theoretical model is constructed and tested based on the use of a high accuracy abinitio dipole moment curve and a semi-empirical potential energy curve. Accurate studies of high overtone transitions provide a challenge to both experiment and theory as the lines are very weak: below 2 × 10-29cmmolecule-1 at 296K. Agreement between theory and experiment within the experimental uncertainty of a few percent is obtained. However, this agreement is only achieved after issues with the stability of the Davidson correction to the multi-reference configuration interaction calculations are addressed.

Optical pressure sensing at MHz rates via collisional line broadening of carbon monoxide: uncertainty quantification in reacting flows

An optical method for high-speed line-of-sight pressure measurements using infrared laser absorption spectroscopy is presented with detailed uncertainty analysis related to thermodynamic and compositional variation in combustion environments. The technique exploits simultaneous sub-microsecond sensing of temperature and mole fraction to extract pressure from collisional line broadening at MHz rates. A distributed-feedback quantum-cascade laser near 5 upmu m in a bias-tee circuit is used to spectrally resolve multiple rovibrational transitions in the P-branch of the fundamental band of carbon monoxide, which may be seeded or nascent to reacting flows. A comprehensive approach for estimating collisional line broadening in complex combustion gas mixtures is presented. Uncertainty is quantified for a wide range of conditions, reflecting different fuels, equivalence ratios, reaction progress, and combustion modes (deflagration and detonation), which influence gas composition and temperature. The sensor was evaluated for accuracy and precision in both a high-enthalpy shock-tube facility in hydrocarbon–air ignition experiments and behind ethylene–oxygen detonation waves in a detonation-impulse tube facility at temperatures from 1500 to 3000 K and pressures from 0.5 to 10 bar. Pressure measurements were compared to measurements by piezoelectric pressure transducers and to theoretical estimates from normal-shock and Chapman-Jouguet simulations. The high-speed path-integrated optical pressure measurement offers an alternative to traditional electromechanical transducers that are constrained to values at wall boundaries and have proven unreliable in some harsh reacting flows.

Methyl methacrylate thermal decomposition: Modeling and laser spectroscopy of species time-histories behind reflected shock waves

The thermal decomposition of methyl methacrylate (MMA) was studied through species time-history measurements of formaldehyde (CH2O), carbon monoxide (CO), and carbon dioxide (CO2) behind reflected shock waves over a temperature range of 1200–1600 K near 1 atm. Tunable laser absorption spectroscopy was employed to spectrally and temporally-resolve a cluster of rovibrational lines in the Q-branches of the v1 fundamental band and the v2+v4 combination band of CH2O near 3.60μm, three rovibrational transitions in the P-branch of the fundamental band of CO near 4.98μm, and a transition in the R-branch of the (0100→0101) v3 band of CO2 near 4.19μm. Spectral fitting procedures are subsequently used to infer CO, CO2, and CH2O mole fraction during the pyrolysis of shock-heated mixtures of MMA in argon. These data provided valuable experimental constraints on MMA pyrolysis chemical kinetic models. Sensitivity analysis of a detailed chemical model for MMA decomposition identified specific reactions likely to account for differences observed between the species measurements and simulations of the test conditions. Modified reaction rate parameters for select MMA decomposition reactions are proposed, determined via a genetic algorithm optimization procedure anchored to the speciation data.

Line mixing study of carbon monoxide near [formula omitted] broadened by nitrogen, helium, and hydrogen

We present quantitative, broadband absorbance measurements of the fundamental rovibrational band of carbon monoxide (CO) between 1965 and 2230 cm−1 in bath gases of nitrogen (N2), helium (He), and hydrogen (H2). These measurements are then compared to two constructed models capable of reproducing the effects of line mixing present in our measured results. The static cell measurements were taken using a narrow-linewidth, broad-scan external-cavity quantum-cascade laser at pressures of 15–35 atm and temperatures of 293, 453 (CO/H2) and 802 K (CO/N2, CO/He). Our first line mixing approach, based on the modified exponential gap (MEG) law with a fitted inter-branch factor, shows improved agreement with the measured spectra across different pressures and broadening partners relative to purely Lorentzian models. At the elevated temperatures, similar agreement is observed; however, a mismatch is present between extrapolated HITRAN broadening parameters and those observed in the measured spectra. This is likely due to the known deficiency of the single power law over large temperature ranges, and hence a minor scaling of the line-by-line temperature-dependence exponents is incorporated that is supported by previous studies in the literature. Our second, more empirical line mixing approach involves extracting MEG line mixing parameters through a direct fit to the measured spectra. The Direct Fit method bypasses the need for known line shape parameters and produces even stronger agreement with measured data, with a CO/H2 root-mean-square error of 0.4% at the highest-number-density condition of 293 K and 35 atm. The line mixing models presented and discussed will be useful for interpreting future satellite and telescope observations of CO from deeper, higher-number-density layers of exoplanetary gas-giant atmospheres, consisting of mainly H2 and He.

Chromospheric Carbon Monoxide Formation around a Solar Pore

We present observations of NOAA AR 11159, obtained on 2011 February 14 in the 4.7 μm band of carbon monoxide (CO) and coordinated with spectroscopic imaging of three atomic lines (Na i 5896 Å, Fe i 7090 Å, and Ca ii 8542 Å) which sample heights from the mid-photosphere to the chromosphere. Phase-difference spectra between the observed spectral lines instead indicate that the CO lines form at z ≈ 530−650 km in the quiet Sun. During the two hours of observations, seven long-lived cooling events (“cold bubbles”) were observed in CO in the region surrounding a large pore, but were not visible in the three atomic lines. These events show self-similar temporal evolution with time scales consistent with the chemical formation rate of CO at z ≈ 1000 km. Due to the lack of such features in the surrounding quiet Sun, we hypothesize that the magnetic canopy field surrounding the pore, which suppresses the upward propagation of acoustic waves into the chromosphere and the subsequent formation of shocks, depresses the rate of acoustic heating and allows CO to condense and cool the atmosphere at those heights. These “cold bubbles” may be a source of the chromospheric CO that produces the unexpectedly high (z ≈ 1000 km) limb extensions seen in the stronger CO lines, and may provide a unique opportunity to study this enigmatic component of the solar atmosphere in spatially resolved observations.

Effect of the analytical form of the dipole-moment function on the rotational intensity distributions in the high-overtone vibrational bands of carbon monoxide

For modelling the line intensities of the low-overtone bands (Δv≤3 in CO), any potential-energy and dipole-moment functions (PEFs and DMFs) that describe the available data can be used. This is not true for the high-overtone bands. The Born-Oppenheimer molecular functions as functions of the interatomic separation r must obey some restrictions in the complex plane of r. In particular, the PEF and DMF must have common singularities in the complex plane and the DMF should not rapidly increase upon displacement from the real axis. Two model DMFs are considered for CO, a fully regular function over the entire complex plane and an irregular one with two branch points corresponding to complex intersections of the ground-state PEF with the excited-states ones. The predictions of the 7-0 band made with the regular DMF turn out to be unstable with respect to small variations in the database, which is associated with very rapid variations of this DMF. On the contrary, the predictions of the irregular one are stable and therefore are considered to be more reliable.

Thermal Treatment Effect on CO and NO Adsorption on Fe(II) and Fe(III) Species in Fe3O-Based MIL-Type Metal-Organic Frameworks: A Density Functional Theory Study.

The properties of metal–organic frameworks (MOFs) based on triiron oxo-centered (Fe3O) metal nodes are often related to the efficiency of the removal of the solvent molecules and the counteranion chemisorbed on the Fe3O unit by postsynthetic thermal treatment. Temperature, time, and the reaction environment play a significant role in modifying key features of the materials, that is, the number of open metal sites and the reduction of Fe(III) centers to Fe(II). IR spectroscopy allows the inspection of these postsynthetic modifications by using carbon monoxide (CO) and nitric oxide (NO) as probe molecules. However, the reference data sets are based on spectra recorded for iron zeolites and oxides, whose structures are different from the Fe3O one. We used density functional theory to study how the adsorption enthalpy and the vibrational bands of CO and NO are modified upon dehydration and reduction of Fe3O metal nodes. We obtained a set of theoretical spectra that can model the modification observed in previously reported experimental spectra. Several CO and NO bands were previously assigned to heterogeneous Fe(II) and Fe(III) sites, suggesting a large defectivity of the materials. On the basis of the calculations, we propose an alternative assignment of these bands by considering only crystallographic iron sites. These findings affect the common description of Fe3O-based MOFs as highly defective materials. We expect these results to be of interest to the large community of scientists working on Fe(II)- and Fe(III)-based MOFs and related materials.

Exploiting night-time averaged spectra from PFS/MEX shortwave channel. Part 1: Temperature retrieval from the CO2ν3 band

Nadir remote sensing of the night side of Mars is challenging, mainly due to the low signal-to-noise ratio of such observations. We show in a companion paper that the abundance of carbon monoxide (CO) during night can be retrieved from the observations of the Planetary Fourier Spectrometer (PFS). This requires, however, an accurate knowledge of the temperature profile, and especially of the night-time thermal inversions, to properly model the atmospheric emission. While the temperature profile is usually retrieved from the ν2 band of CO2 (centered at 667 ​cm−1), this work shows that, for averaged night-time PFS observations built from a large ensemble of spectra, the temperature profile can be retrieved from the more saturated ν3 band of CO2 (centered at 2349 ​cm−1). We show especially that, due to IFOV (instantaneous field-of-view) size differences and boresight offset between the longwave and shortwave channels of PFS, the temperature profile retrieved from the ν3 band is more consistent with the emission observed in the 1-0 band of CO (centered at 2143 ​cm−1), which is used in the second part paper. We provide a complete characterization of the retrieved temperature profiles in terms of error and vertical sensitivity. Using this, we show that using the ν3 CO2 band allows to properly constrain and characterize the thermal inversions encountered near the surface for most night-time observations. The resulting set of temperature profiles is essential for the retrieval of the night-time CO abundance that is presented in the companion paper. Beyond their usefulness for the night-time CO retrieval, we suggest with a last example that temperature profiles retrieved from the ν3 band of CO2 could be use more generally to study surface thermal inversions encountered at night.

Time-resolved Fourier transform infrared emission spectroscopy of CO ∆v = 1 and ∆v = 2 extended bands in the ground X1Σ+ state produced by formamide glow discharge

This paper presents an extension to our knowledge of ∆v = 1 and ∆v = 2 bands of carbon monoxide in the ground state, measured by Fourier transform infrared spectroscopy of glow discharge of formamide-nitrogen mixture. Lines in declared bands are measured up to v = 30 for ∆v = 1 and up to v = 24 for ∆v = 2 band, by use of both InSb and MCT detectors, which have not been measured in the laboratory before. Dunham parameters obtained by fitting our lines are presented as well as comparison to other authors. The paper also demonstrates the interesting impossibility of sufficient population of ∆v = 2 band of CO when only pure CO is used in the glow discharge, instead of formamide-based mixture. Additionally, we present a non-LTE model to describe the intensity pattern of the ∆v = 1 and the ∆v = 2 bands of 12C16O experimental spectra by simulating the corresponding non-LTE vibrational populations of CO.

Line parameters of the 4-0 band of carbon monoxide by high sensitivity cavity ring down spectroscopy near 1.2 µm

The room temperature spectrum of the very weak third overtone band of carbon monoxide in natural isotopic abundance is recorded by cavity ring down spectroscopy (CRDS) referenced to a frequency comb, between 8206 and 8465 cm−1. The sensitivity of the recordings (noise equivalent absorption on the order of αmin ∼ 5 × 10−12 cm−1) allowed for measuring lines with intensity as weak as 1 × 10−30 cm/molecule at a recording pressure limited to 10.0 Torr. The use of low pressure values (1.0 and 10.0 Torr) helped to minimize the impact of profile effects on the derived line positions and line intensities. The line profile analysis was performed using the speed dependent Nelkin-Ghatak model for the 10 Torr recordings while the Voigt profile was found sufficient to account for the line shapes recorded at 1.0 Torr.Overall, line parameters of 227 transitions are derived. The observed transitions belong to the 4-0 band of the 12C16O, 13C16O, 12C18O and 12C17O isotopologues present in natural abundance in the sample and to the 5-1 hot band of 12C16O. For a large part of the observations, line positions are reported with accuracy as good as 4 × 10−6 cm−1 (∼120 kHz). The self-induced line shift of the 4-0 band is reported for the first time from the position values at 1 and 10 Torr. Using literature values of the 1-0, 2-0 and 3-0 bands, the vibrational dependence of the self-induced pressure shift in CO is discussed. The experimental values of the 12C16O v = 4 energy levels J < 26 are reproduced with a standard deviation of 2.5 × 10−6 cm−1 (75 kHz). The intensities of the 12C16O lines reported with an accuracy better than 1% show an overall good agreement with literature values in particular with those included in the HITRAN database.

Mid-Infrared Quartz-Enhanced Photoacoustic Sensor for ppb-Level CO Detection in a SF6 Gas Matrix Exploiting a T-Grooved Quartz Tuning Fork.

An optical sensor for highly sensitive detection of carbon monoxide (CO) in sulfur hexafluoride (SF6) was demonstrated by using the quartz-enhanced photoacoustic spectroscopy technique. A spectrophone composed of a custom 8 kHz T-shaped quartz tuning fork with grooved prongs and a pair of resonator tubes, to amplify the laser-induced acoustic waves, was designed aiming to maximize the CO photoacoustic response in SF6. A theoretical analysis and an experimental investigation of the influence of SF6 gas matrix on spectrophone resonance properties for CO detection have been provided, and the performances were compared with the standard air matrix. A mid-infrared quantum cascade laser with a central wavelength at 4.61 μm, resonant with the fundamental band of CO, and an optical power of 20 mW was employed as the light excitation source. A minimum detection limit of 10 ppb at 10 s of integration time was achieved, and a sensor response time of ∼3 min was measured.

Tracking the atmospheric pulse of a North American megacity from a mountaintop remote sensing observatory

Atmospheric carbon monoxide (CO) is an effective tracer for monitoring atmospheric transport processes and for detecting pollution sources of anthropogenic origin. However, very few observation systems exist that are capable of providing measurements with high spatial and temporal resolution to identify hotspots for emission control purposes. Here we introduce a mountain-top remote sensing observatory, the California Laboratory for Atmospheric Remote Sensing (CLARS), for mapping the enhancement of CO column-averaged mixing ratio (XCO) over the Los Angeles (LA) megacity. Compared to conventional observation network, CLARS is unique in the following ways: (1) it mimics a geostationary satellite observatory for LA with approximately hourly- and kilometer-scale mapping capability; (2) the free tropospheric background atmosphere is simultaneously measured; and (3) the measurements are highly sensitive to anthropogenic emissions due to the long light path along the planetary boundary layer (PBL). The CO slant column density and XCO are retrieved from reflected sunlight measurements in the 2.3 μm CO band and the 1.27 μm oxygen (O2) band. Data filtering and corrections for aerosol scattering and geometric effects are then implemented to derive the XCO enhancement, which is the XCO excess in the PBL compared to the background value. In the LA megacity, the XCO enhancement shows a distinctive diurnal cycle primarily driven by changes in anthropogenic emissions and sea-breeze circulation. Such diurnal patterns can be reproduced by the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The enhancement also shows a significant weekly cycle resulting from the weekly pattern in anthropogenic CO emissions. On average, the XCO enhancements on Sunday and Saturday are 16.1% and 4.4%, respectively, lower than weekday values. The weekly XCO enhancement patterns also show high correlation with traffic counts. A seasonal pattern of XCO enhancement with high (low) spatial contrast in summer (winter), resulting from changing sea-breeze circulation, can be observed. These diurnal, weekly, and seasonal patterns of XCO enhancement serve as tracers of the atmospheric pulse of the LA megacity. The CLARS observatory can serve as a testbed for future geostationary missions to track anthropogenic emissions in cities.

Laser Remote Sensing Method of Carbon Monoxide Emissions Detection

Monitoring of atmospheric gas pollution is one of the most important environmental target. Laser methods are the most effective for remote operational monitoring of atmospheric pollution.One of the most important air pollutants is carbon monoxide.The article analyzes the possibility of laser remote sensing method of carbon monoxide emissions detection in atmosphere.The information parameter measured by the remote sensing laser gas analyzer was assessed for absorption band of carbon monoxide near 2,3 μm.The information parameter that can be used for monitoring monoxide emissions is the ratio of the power of laser signals at the wavelengths 4295 cm-1 and 4370 cm-1.Results of calculations of the information parameter for different sizes of emissions (from 1 m to 100 m) and different content of carbon monoxide in the emission (from 0.01 % to 10 %) were showed.Comparing the information parameter R with its background value shows that carbon monoxide emissions can be monitored.Mathematical modeling was performed for quantitative estimation the reliability of detecting carbon monoxide emissions.The probability of correctly emission detecting (emission detecting when there is one) and the probability of false alarms (emission detecting when there is none) were calculated.Mathematical modelling shows that a laser gas analyzer allows us to detect the carbon monoxide emissions with correct detection probability not less 0,845 and false alarm probability no more 0,243 for carbon monoxide emissions with gas concentration not less 0,1 % and dimension of emissions cloud not less 10 m. For carbon monoxide emissions with gas concentration not less 1 % and dimension of emissions cloud not less 5 m a laser gas analyzer allows us to detect the carbon monoxide emissions with correct detection probability not less 0,999 and false alarm probability no more 0,001.

MHz-rate scanned-wavelength direct absorption spectroscopy using a distributed feedback diode laser at 2.3 µm

This paper demonstrates scanned-wavelength tunable diode laser absorption spectroscopy (TDLAS) with a scan rate up to 2 MHz using a distributed feedback (DFB) diode laser. The 2.3-µm DFB laser was used to probe the R(11) line present in the first overtone band of carbon monoxide (CO). Detailed tuning characteristics of the DFB laser were investigated over a wide range of scan rates from 20 kHz to 2 MHz. The tuning range was found to decrease exponentially with the scan rate below 1 MHz, and then slightly decrease up to 2 MHz. By applying a sinusoidal waveform to the injection current, the phase shift (ϕ) between intensity and frequency modulations was measured to be 1.11π at the scan rate of 20 kHz, which increases to 1.61π at 2 MHz. Due to the significant variation of ϕ with the scan rate, the position of the target absorption profile on the transmitted laser intensity curve must be adjusted accordingly based on the simultaneously recorded etalon signal. All the measurements obtained at different scan rates show excellent consistency in the CO spectrum. This study reveals that MHz-rate scanned-wavelength direct absorption spectroscopy can be developed for ultrafast gas sensing that may find promising applications in many fields.

Cross-band infrared laser absorption of carbon monoxide for thermometry and species sensing in high-pressure rocket flows

A novel cross-band laser absorption spectroscopy technique has been developed for quantitative measurements of gas temperature and carbon monoxide (CO) in high-pressure, high-temperature rocket combustion flows. The strategy enables a broad range of sensor operability by simultaneously probing rovibrational transitions in both the fundamental and first overtone bands of CO near $$4.98\,\upmu \hbox {m}$$ and $$2.32\,\upmu \hbox {m}$$, respectively, which sustain large differences in temperature dependence despite collisional broadening. Scanned-wavelength modulation spectroscopy methods are integrated for noise rejection in the harsh rocket operating environment. Initial experiments using the cross-band thermometry technique have been conducted on a single-element-injector rocket combustor with RP-2/GOx and $${\hbox {CH}_4}/\hbox {GOx}$$ propellant combinations at pressures up to 75 bar. Measurements of the first overtone bandhead ($$2.32\,\upmu \hbox {m}$$) maintained adequate signal-to-noise at even higher pressures (up to 105 bar), although deviating significantly from spectral simulations. To account for collisional effects at high gas densities, empirical models for line mixing, developed via shock tube studies, were employed to enable quantitative interpretation of measured signals for temperature and CO mole fraction in the rocket combustor.

Retrieval and characterization of carbon monoxide (CO) vertical profiles in the Martian atmosphere from observations of PFS/MEX

The knowledge of the carbon monoxide (CO) abundance on Mars is essential in order to assess the processes driving the carbon cycle on the planet. Solar occultation measurements provide vertically-resolved measurements of CO from a few kilometers to higher altitudes and can be complemented by nadir measurements to enhance the spatial coverage of observations and the monitoring of the near-surface layer. Up to now, in the shortwave, CO retrievals from nadir observations have, however, mostly been performed on mean spectra and only total column abundances have been obtained. In this work we explore the possibility of exploiting nadir measurements from the Planetary Fourier Spectrometer (PFS) in the 1–0 band of CO (centered at 2143 cm−1) to retrieve vertical profiles of that species on individual measurement. The retrievals are performed for a set of 16 selected PFS spectra with reasonable signal-to-noise ratios by applying the Optimal Estimation Method (OEM) with appropriate constraints, built from model simulations of the Martian atmosphere. The retrieved profiles are characterized in terms of vertical sensitivity and errors. We demonstrate, in particular, that the PFS nadir measurements carry information mostly on the CO column below 15 km, with a maximum sensitivity to the near-surface atmosphere. These measurements allow to substantially reduce the prior uncertainty on the CO abundance in this altitude range, with an estimated total retrieval error on the column-averaged volume mixing ratio (VMR) around 10%. We show that the set of retrieved VMRs are in the range of values reported from other instruments. The retrieved VMRs also capture well the known spatial and seasonal CO variability, which is promising in the perspective of better exploiting the exceptional set of PFS observations on Mars.

Metrological quantification of CO in biogas using laser absorption spectroscopy and gas chromatography

Biogas has a vital role in the future market for renewable energy. When upgraded to biomethane, it can be injected into natural gas grids if the level of certain impurities complies with the specifications in EN16723. For some of these impurities, suitable measurement methods are lacking which hamper the quality control of biomethane to be injected into natural gas networks. Here, we report on the evaluation of three detection methods suitable for carbon monoxide (CO) in biogas and biomethane applications for which EN16723 specifies an upper limit of 0.1% (1000 µmol ⋅ mol−1). Two of these methods are based on laser absorption spectroscopy (LAS) and one on gas chromatography (GC). Both LAS spectrometers employ direct absorption spectroscopy and operate at 4.6 µm, probing a single CO absorption line in the fundamental CO band. One of them, direct tunable diode laser absorption spectroscopy (dTDLAS), is based on a new interband cascade laser specially designed for biogas and biomethane applications, while the other is based on quantum cascade laser absorption spectroscopy (QCLAS). The GC is equipped with two packed columns (HayeSep Q and molecular sieve 5A) and a thermal conductivity detector. CO amount fraction results in biogas matrices derived using these three measurement methods and are compared to amount fraction values of different, gravimetrically prepared reference gas standards of CO in biogas. These were used to validate the measurement capabilities. The measured CO amount fraction results from LAS and GC covered 10–30 000 µmol ⋅ mol−1 (system measurement ranges, LAS: 3–1000 µmol ⋅ mol−1, GC: 500–30 000 µmol ⋅ mol−1) and were in excellent agreement with the gravimetric values of the gas standards. At 400 µmol ⋅ mol−1, the guide to the expression of uncertainty in measurement compliant relative standard uncertainties of our calibration-free dTDLAS and the gas-calibrated QCLAS systems are estimated to be 1.4% versus 0.5%, respectively. The relative standard uncertainty of the GC CO measurements at 5075 µmol ⋅ mol−1 is 1.3%. This work demonstrates that, by means of GC and LAS, relative standard uncertainties of 1.4% and below can be reached for CO measurements in biogas and that cost-optimized calibration-free approaches not requiring frequent use of gas standards have become available.