Carbon Monoxide Observations Research Articles

CO spectra of the ISM in the Host Galaxies of the most luminous WISE-selected AGNs

Abstract We present observations of mid-J (J = 4–3 or J = 5–4) carbon monoxide (CO) emission lines and continuum emission from a sample of ten of the most luminous (Lbol ≥ 1014 L$\rm \odot$) Hot Dust-Obscured Galaxies (Hot DOGs) discovered by the Wide-field Infrared Survey Explorer (WISE) with redshifts up to 4.6. We uncover broad spectral lines (FWHM ≥ 400 km s−1) in these objects, suggesting a turbulent molecular interstellar medium (ISM) may be ubiquitous in Hot DOGs. A halo of molecular gas, extending out to a radius of 5 kpc is observed in W2305–0039, likely supplied by 940 km s−1 molecular outflows. W0831+0140 is plausibly the host of a merger between at least two galaxies, consistent with observations made using ionized gas. These CO(4–3) observations contrast with previous CO(1–0) studies of the same sources: the CO(4–3) to CO(1–0) luminosity ratios exceed 300 in each source, suggesting that the lowest excited states of CO are underluminous. These findings show that the molecular gas in Hot DOGs is consistently turbulent, plausibly a consequence of AGN feedback, triggered by galactic mergers.

Recent decline in carbon monoxide levels observed at an urban site in Ahmedabad, India.

Carbon monoxide (CO) is a prominent air pollutant in cities, with far-reaching implications for both local air quality and global atmospheric chemistry. The long-term change in atmospheric CO levels at a specific location is influenced by a complex interplay of local emissions, atmospheric transport, and photochemical processes, making it a subject of considerable interest. This study presents an 8-year analysis (2014-2021) of in situ CO observations using a cutting-edge laser-based analyzer at an urban site in Ahmedabad, western India. The long-term observations reveal a subtle trend in CO levels, masked by contrasting year-to-year variations, particular after 2018, across distinct diurnal time windows. Mid-afternoon (12:00-16:00h) CO levels, reflecting background and regional conditions, remained relatively stable over the study period. In contrast, evening (18:00-21:00h) CO levels, influenced by local emissions, exhibited substantial inter-annual variability without discernible trends from 2014 to 2018. However, post-2018, evening CO levels showed a consistent decline, predating COVID-19 lockdown measures. This decline coincided with the nationwide adoption of Bharat stage IV emission standards and other measures aimed at reducing vehicular emissions. The COVID-19 lockdown in 2020 further resulted in a noteworthy 29% reduction in evening CO levels compared to the pre-lockdown (2014-2019) period, highlighting the potential for substantial CO reduction through stringent vehicular emission controls. The observed long-term changes in CO levels do not align with the decreasing emission estimated by various inventories from 2014 to 2018, suggesting a need for improved emission statistics in Indian urban regions. This study underscores the importance of ongoing continuous CO measurements in urban areas to inform policy efforts aimed at controlling atmospheric pollutants.

First Extragalactic Detection of Thermal Hydroxyl (OH) 18 cm Emission in M31 Reveals Abundant CO-faint Molecular Gas

The most abundant interstellar molecule, molecular hydrogen (H2), is practically invisible in cold molecular clouds. Astronomers typically use carbon monoxide (CO) to trace the bulk distribution and mass of H2 in our galaxy and many others. CO observations alone fail to trace a significant component of molecular gas known as “CO-dark” molecular gas, which can be probed with molecules such as OH and CH. We present an extremely sensitive pilot search for the 18 cm hydroxyl (OH) lines in the Andromeda galaxy (M31) with the 100 m Robert C. Byrd Green Bank Telescope. We successfully detected the 1665 and 1667 MHz OH lines in faint emission. The 1665/1667 MHz line ratio displays the characteristic 5:9 ratio predicted under conditions of local thermodynamic equilibrium. To our knowledge, this is the first detection of nonmaser 18 cm OH emission in another galaxy. We compare our OH and H i observations with archival CO (1–0) observations. Our OH detection position overlaps with the previously discovered Arp Outer Arm in CO. Our best estimates show that the amount of H2 traced by OH is 100%–140% higher than the amount traced by CO in this sight line. The amount of dark molecular gas implied by dust data supports this conclusion. We conclude that the 18 cm OH lines hold promise as a valuable tool for mapping of the “CO-dark” and “CO-faint” molecular gas phase in nearby galaxies, especially with upcoming multibeam, phased-array feed receivers on radio telescopes, which will allow for drastically improved mapping speeds of faint signals.

TROPESS-CrIS CO single-pixel vertical profiles: intercomparisons with MOPITT and model simulations for 2020 western US wildfires

Abstract. The new TROPESS (TRopospheric Ozone and its Precursors from Earth System Sounding) profile retrievals of carbon monoxide (CO) from the Cross-track Infrared Sounder (CrIS) are evaluated against Measurement of Pollution in the Troposphere (MOPITT) CO version 9 data. Comparison results that were adjusted to common a priori constraints in the retrieval processes have improved agreement between the two data sets over direct comparisons. TROPESS-CrIS CO profiles are within 5 % of MOPITT but have higher concentrations in the lower troposphere and lower concentrations in the upper troposphere. For the intense western US wildfire events in September 2020, we compare CO fields simulated by the GISS climate model to the two satellite CO observations. We show intermediate steps of the comparison process to illustrate the evaluation of model simulations by deriving the “retrieved” model CO profiles as they would be observed by the satellite. This includes the application of satellite level-2 data along with their corresponding diagnostic operators provided in the TROPESS-CrIS and MOPITT products. The process allows a diagnosis of potential model improvements in modeling fire emissions and pollution transport.

Identifying episodic carbon monoxide emission events in the MOPITT measurement dataset

Abstract. The Measurements Of Pollution In The Troposphere (MOPITT) instrument aboard NASA's Terra satellite has been measuring upwelling radiance in a nadir-viewing mode since March 2000. These radiance measurements are inverted to yield estimates of carbon monoxide (CO) profiles and total columns, providing the longest satellite record of this trace gas to date. The CO measurements from MOPITT have been used in a variety of ways, including trend analyses and the construction of CO budgets. However, their use is complicated by the influence of episodic emission events, which release large quantities of CO into the atmosphere with irregular timing, such as large sporadic wildfires of natural or anthropogenic origin. The chaotic nature of these events is a large source of variability in CO budgets and models, requiring that these events be well characterized in order to develop an improved understanding of the role they have in influencing tropospheric CO. This study describes the development of a multistep algorithm that is used to identify large episodic emission events using daily mean Level 2 (L2) MOPITT total column measurements gridded to a 0.5 by 0.5° spatial resolution. The core component of this procedure involves empirically determining the expectation density function (EDF) that describes the departure of daily-mean CO observations from the baseline behaviour of CO, as described by its periodic components and trends. The EDFs employed are not assumed to be symmetric but instead are constructed from a pair of superimposed normal distributions. Enhancement flag files are produced following this methodology, identifying the episodic events that show strong enhancement of CO outside of the range of expected CO behaviour and are now made available for the period 3 March 2000 to 31 July 2022. The distribution and frequency of these flagged measurements over this 22-year period are analyzed in order to illustrate the robustness of this method.

Advantages of assimilating multispectral satellite retrievals of atmospheric composition: a demonstration using MOPITT carbon monoxide products

Abstract. The Measurements Of Pollution In The Troposphere (MOPITT) is an ideal instrument to understand the impact of (1) assimilating multispectral and joint retrievals versus single spectral products, (2) assimilating satellite profile products versus column products, and (3) assimilating multispectral and joint retrievals versus assimilating individual products separately. We use the Community Atmosphere Model with chemistry with the Data Assimilation Research Testbed (CAM-chem+DART) to assimilate different MOPITT carbon monoxide (CO) products to address these three questions. Both anthropogenic and fire CO emissions are optimized in the data assimilation experiments. The results are compared with independent CO observations from TROPOspheric Monitoring Instrument (TROPOMI), the Total Carbon Column Observing Network (TCCON), NOAA Carbon Cycle Greenhouse Gases (CCGG) sites, In-service Aircraft for a Global Observing System (IAGOS), and Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN). We find that (1) assimilating the MOPITT joint (multispectral; near-IR and thermal IR) column product leads to better model–observation agreement at and near the surface than assimilating the MOPITT thermal-IR-only column retrieval. (2) Assimilating column products has a larger impact and improvement for background and large-scale CO compared to assimilating profile products due to vertical localization in profile assimilation. However, profile assimilation can outperform column assimilations in fire-impacted regions and near the surface. (3) Assimilating multispectral and joint products results in similar or slightly better agreement with observations compared to assimilating the single spectral products separately.

Intoxication au monoxyde de carbone chez les enfants

Introduction: Carbon monoxide (CO) poisoning is a common pathology responsible for high morbidity and mortality worldwide. Few studies in Tunisia have focused on the pediatric population.Aim: The purpose of this study was to determine the epidemiological profile of CO poisoning as well as its clinical, paraclinical, therapeutic and evolutionary aspects.Methods: Our study included observations of CO poisoning in children hospitalized in the pediatric department C of the children's hospital in Tunis, over a period of 3 years.Results: We have collected 199 cases of CO poisoning in children. The average age was 5.43 years with a sex ratio of 0.98. The source of CO was inside the home in 73.2 % of cases and it was the gas bath heater in 68.8 % of cases. The intoxication was collective in 94.9 % of the cases and it occurred during the month of January in 35.8 % of the cases. The clinical manifestations were headaches in 69 % of cases. The rate of carboxyhemoglobin was pathological in 73.9 % of cases. All patients received normobaric oxygen therapy and only 3.6 % of patients had a hyperbaric oxygen therapy session. We did not deplore any case of death in our study.Conclusion: CO poisoning remains a public health problem in our country with high morbidity. The risk of secondary complications, particularly neuropsychiatric, requires clinical and possibly neuroradiological monitoring of these victims.

Constraining the H2 column densities in the diffuse interstellar medium using dust extinction and H I data

Context. Carbon monoxide (CO) is a poor tracer of H2 in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules, unlike the situation at higher extinctions. Aims. We present a novel, indirect method for constraining H2 column densities (NH2) without employing CO observations. We show that previously recognized nonlinearities in the relation between the extinction, AV (H2), derived from dust emission and the H I column density (NH I) are due to the presence of molecular gas. Methods. We employed archival (NH2) data, obtained from the UV spectra of stars, and calculated AV(H2) toward these sight lines using 3D extinction maps. The following relation fits the data: log NH2 = 1.38742 (log AV(H2))3 − 0.05359 (log AV(H2))2 + 0.25722 log AV(H2) + 20.67191. This relation is useful for constraining NH2 in the diffuse ISM as it requires only NH I and dust extinction data, which are both easily accessible. In 95% of the cases, the estimates produced by the fitted equation have deviations of less than a factor of 3.5. We constructed a NH2 map of our Galaxy and compared it to the CO integrated intensity (WCO) distribution. Results. We find that the average ratio (XCO) between NH2 and WCO is approximately equal to 2 × 1020 cm−2 (K km s−1 )−1, consistent with previous estimates. However, we find that the XCO factor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions with NH2 ≳ 1020 cm−2, we estimate that the average H2 fractional abundance, fH2 = 2 NH2/(2NH2 + NH I), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (AV ≥ 1 mag), hence limiting fH2 in these directions. Conclusions. More than 50% of the lines of sight with NH2 ≥ 1020 cm−2 are untraceable by CO with a J = 1−0 sensitivity limit WCO = 1 K km s−1.

Southern Hemisphere atmospheric history of carbon monoxide over the late Holocene reconstructed from multiple Antarctic ice archives

Abstract. Carbon monoxide (CO) is a naturally occurring atmospheric trace gas, a regulated pollutant, and one of the main components determining the oxidative capacity of the atmosphere. Evaluating climate–chemistry models under different conditions than today and constraining past CO sources requires a reliable record of atmospheric CO mixing ratios ([CO]) that includes data since preindustrial times. Here, we report the first continuous record of atmospheric [CO] for Southern Hemisphere (SH) high latitudes over the past 3 millennia. Our continuous record is a composite of three high-resolution Antarctic ice core gas records and firn air measurements from seven Antarctic locations. The ice core gas [CO] records were measured by continuous flow analysis (CFA), using an optical feedback cavity-enhanced absorption spectrometer (OF-CEAS), achieving excellent external precision (2.8–8.8 ppb; 2σ) and consistently low blanks (ranging from 4.1±1.2 to 7.4±1.4 ppb), thus enabling paleo-atmospheric interpretations. Six new firn air [CO] Antarctic datasets collected between 1993 and 2016 CE at the DE08-2, DSSW19K, DSSW20K, South Pole, Aurora Basin North (ABN), and Lock-In sites (and one previously published firn CO dataset at Berkner) were used to reconstruct the atmospheric history of CO from ∼1897 CE, using inverse modeling that incorporates the influence of gas transport in firn. Excellent consistency was observed between the youngest ice core gas [CO] and the [CO] from the base of the firn and between the recent firn [CO] and atmospheric [CO] measurements at Mawson station (eastern Antarctica), yielding a consistent and contiguous record of CO across these different archives. Our Antarctic [CO] record is relatively stable from −835 to 1500 CE, with mixing ratios within a 30–45 ppb range (2σ). There is a ∼5 ppb decrease in [CO] to a minimum at around 1700 CE during the Little Ice Age. CO mixing ratios then increase over time to reach a maximum of ∼54 ppb by ∼1985 CE. Most of the industrial period [CO] growth occurred between about 1940 to 1985 CE, after which there was an overall [CO] decrease, as observed in Greenland firn air and later at atmospheric monitoring sites and attributed partly to reduced CO emissions from combustion sources. Our Antarctic ice core gas CO observations differ from previously published records in two key aspects. First, our mixing ratios are significantly lower than reported previously, suggesting that previous studies underestimated blank contributions. Second, our new CO record does not show a maximum in the late 1800s. The absence of a [CO] peak around the turn of the century argues against there being a peak in Southern Hemisphere biomass burning at this time, which is in agreement with (i) other paleofire proxies such as ethane or acetylene and (ii) conclusions reached by paleofire modeling. The combined ice core and firn air [CO] history, spanning −835 to 1992 CE, extended to the present by the Mawson atmospheric record, provides a useful benchmark for future atmospheric chemistry modeling studies.

The capabilities of the adjoint of GEOS-Chem model to support HEMCO emission inventories and MERRA-2 meteorological data

Abstract. The adjoint of the GEOS-Chem (Goddard Earth Observing System with Chemistry) model has been widely used to constrain the sources of atmospheric compositions. Here, we designed a new framework to facilitate emission inventory updates in the adjoint of the GEOS-Chem model. The major advantage of this new framework is good readability and extensibility, which allows us to support Harmonized Emissions Component (HEMCO) emission inventories conveniently and to easily add more emission inventories following future updates in GEOS-Chem forward simulations. Furthermore, we developed new modules to support MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) meteorological data, which allows us to perform long-term analyses with consistent meteorological data for the period 1979–present. The performances of the developed capabilities were evaluated with the following steps: (1) diagnostic outputs of carbon monoxide (CO) sources and sinks to ensure the correct reading and use of emission inventories, (2) forward simulations to compare the modeled surface and column CO concentrations among various model versions, (3) backward simulations to compare adjoint gradients of global CO concentrations to CO emissions with finite-difference gradients, and (4) observing system simulation experiments (OSSEs) to evaluate the model performance in 4D variational (4D-Var) assimilations. Finally, an example application of 4D-Var assimilation was presented to constrain anthropogenic CO emissions in 2015 by assimilating Measurement of Pollution in the Troposphere (MOPITT) CO observations. The capabilities developed in this work are important for better applications of the adjoint of the GEOS-Chem model in the future. These capabilities will be submitted to the standard GEOS-Chem adjoint code base for better development of the community of the adjoint of the GEOS-Chem model.

Wide-field CO isotopologue emission and the CO-to-H2 factor across the nearby spiral galaxy M101

Carbon monoxide (CO) emission constitutes the most widely used tracer of the bulk molecular gas in the interstellar medium (ISM) in extragalactic studies. The CO-to-H2 conversion factor, α12CO(1−0), links the observed CO emission to the total molecular gas mass. However, no single prescription perfectly describes the variation of α12CO(1−0) across all environments within and across galaxies as a function of metallicity, molecular gas opacity, line excitation, and other factors. Using spectral line observations of CO and its isotopologues mapped across a nearby galaxy, we can constrain the molecular gas conditions and link them to a variation in α12CO(1−0). Here, we present new, wide-field (10 × 10 arcmin2) IRAM 30-m telescope 1 mm and 3 mm line observations of 12CO, 13CO, and C18O across the nearby, grand-design, spiral galaxy M101. From the CO isotopologue line ratio analysis alone, we find that selective nucleosynthesis and changes in the opacity are the main drivers of the variation in the line emission across the galaxy. In a further analysis step, we estimated α12CO(1−0) using different approaches, including (i) via the dust mass surface density derived from far-IR emission as an independent tracer of the total gas surface density and (ii) local thermal equilibrium (LTE) based measurements using the optically thin 13CO(1–0) intensity. We find an average value of ⟨α12CO(1 − 0)⟩ = 4.4 ± 0.9 M⊙ pc−2 (K km s−1)−1 across the disk of the galaxy, with a decrease by a factor of 10 toward the 2 kpc central region. In contrast, we find LTE-based α12CO(1−0) values are lower by a factor of 2–3 across the disk relative to the dust-based result. Accounting for α12CO(1−0) variations, we found significantly reduced molecular gas depletion time by a factor 10 in the galaxy’s center. In conclusion, our result suggests implications for commonly derived scaling relations, such as an underestimation of the slope of the Kennicutt Schmidt law, if α12CO(1−0) variations are not accounted for.

Transport pathways of carbon monoxide from Indonesian fire pollution to a subtropical high-altitude mountain site in the western North Pacific

Abstract. Dry conditions associated with the El Niño–Southern Oscillation (ENSO) and a positive Indian Ocean Dipole (IOD) are known to have caused major fire pollution events and intense carbon emissions over a vast spatial expanse of Indonesia in October 2006 and 2015. During these two events, a substantial increase in the carbon monoxide (CO) mixing ratio was detected by in situ measurements at Lulin Atmospheric Background Station (LABS; 23.47∘ N 120.87∘ E; 2862 ma.s.l.) in Taiwan, which is the only background station in the subtropical western North Pacific region. Compared to the long-term October mean (2006–2021), CO was elevated by ∼ 47.2 ppb (parts per billion; 37.2 %) and ∼ 36.7 ppb (28.9 %) in October 2006 and 2015, respectively. This study delineates plausible pathways for the CO transport from Indonesia to LABS using Measurement of Pollution in the Troposphere (MOPITT) CO observations and Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis products (winds and geopotential height – GpH). Two simultaneously occurring transport pathways were identified, namely (i) horizontal transport in the free troposphere and (ii) vertical transport through the Hadley circulation (HC). The GpH analysis of both events revealed the presence of a high-pressure anticyclone over the northern part of the South China Sea (SCS), which played an important role in the free-tropospheric horizontal transport of CO. In this scenario, CO in the free troposphere is transported on the western edge of the high-pressure system and then driven by subtropical westerlies to LABS. Simultaneously, uplifted CO over Indonesia can enter the HC and be transferred to subtropical locations such as LABS. The vertical cross section of the MOPITT CO and MERRA-2 vertical pressure velocity supported the transport of CO through the HC. Furthermore, the results revealed a distinct HC strength in two events (higher in 2006 compared to 2015) due to the different ENSO conditions. Overall, the present findings can provide some insights into understanding the regional transport of pollution over Southeast Asia and the role of climate conditions on transport pathways.

Rapid decline of carbon monoxide emissions in the Fenwei Plain in China during the three-year Action Plan on defending the blue sky

The Fenwei Plain is one of China's most polluted regions, with poor atmospheric dispersion conditions and an outdated energy structure. After implementing multiple policies in recent years, significant reductions in air pollutant concentrations were observed. In this study, based on the Lagrangian-Bayesian inversion framework FLEXINVERT, we constructed a variable resolution inversion system focusing on the Fenwei Plain and inferred the carbon monoxide (CO) emissions using in-situ atmospheric CO observations from April 2014 to March 2020. We analyzed the spatiotemporal variations of the CO emissions and discussed their causes, especially the effect of the “Three-year Action Plan on Defending the Blue Sky” (TAPDBS). Before the policy, CO emissions temporarily increased, and the overall decrease in CO emissions per unit of Gross Domestic Product (GDP) slowed down. When the policy was implemented, CO emission fluxes declined sharply, with an average drop of 28%, accompanied by an even higher 37% decrease of CO emission per GDP. The reasons for the decline in CO emissions in Shanxi, Shaanxi and Henan are diverse. The decrease in energy intensity is the reason for CO emission reduction in Shannxi and Henan province but not in Shanxi province. This research fills the gap in emission information in recent years and confirms that TAPDBS has brought a breakthrough in both economic development and air quality protection in the Fenwei Plain.

Continental-scale Atmospheric Impacts of the 2020 Western U.S. Wildfires

The wildfire season in the Western United States (U.S.) was anomalously large in 2020, with a majority of burned area due to lightning ignitions resulting in overall fire emissions of carbon monoxide (CO) in the Western region almost 3 times the 2001–2019 average. We used the Community Atmosphere Model version 6 with Chemistry (CAM-chem) to investigate how the 2020 fires in the Western U.S. affected air quality locally as well as in surrounding regions that received transported pollution. Simulations with and without fire emissions over the Western U.S. (32.5–49°N, 115–125°W) in July–December 2020 were used to determine average changes in atmospheric composition across the country. Comparisons against satellite and ground-based column CO observations show that the model generally underestimated CO from fires but adequately reproduced spatial and temporal variability. Simulations showed the 2020 fire season contributed 14.5% to atmospheric CO over the Contiguous United States in September, and ∼3% to CO averaged across the Northern Hemisphere; these enhancements lasted several months. Fire emissions in 2020 continued later into the year than usual, resulting in sustained air pollution over the Western U.S. region, with noticeable meridional transport of ozone (O3) and fine particulate matter (PM2.5). Finally, we use the model to identify two transported fire pollution events at Boulder, Colorado.

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.

TROPESS/CrIS carbon monoxide profile validation with NOAA GML and ATom in situ aircraft observations

Abstract. The new single-pixel TROPESS (TRopospheric Ozone and its Precursors from Earth System Sounding) profile retrievals of carbon monoxide (CO) from the Cross-track Infrared Sounder (CrIS) are evaluated using vertical profiles of in situ observations from the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Laboratory (GML) aircraft program and from the Atmospheric Tomography Mission (ATom) campaigns. The TROPESS optimal estimation retrievals are produced using the MUSES (MUlti-SpEctra, MUlti-SpEcies, MUlti-Sensors) algorithm, which has heritage from retrieval algorithms developed for the EOS/Aura Tropospheric Emission Spectrometer (TES). TROPESS products provide retrieval diagnostics and error covariance matrices that propagate instrument noise as well as the uncertainties from sequential retrievals of parameters such as temperature and water vapor that are required to estimate the carbon monoxide profiles. The validation approach used here evaluates biases in column and profile values as well as the validity of the retrieval error estimates using the mean and variance of the compared satellite and aircraft observations. CrIS–NOAA GML comparisons had biases of 0.6 % for partial column average volume mixing ratios (VMRs) and (2.3, 0.9, −4.5) % for VMRs at (750, 511, 287) hPa vertical levels, respectively, with standard deviations from 9 % to 14 %. CrIS–ATom comparisons had biases of −0.04 % for partial column and (2.2, 0.5, −3.0) % for (750, 511, 287) hPa vertical levels, respectively, with standard deviations from 6 % to 10 %. The reported observational errors for TROPESS/CrIS CO profiles have the expected behavior with respect to the vertical pattern in standard deviation of the comparisons. These comparison results give us confidence in the use of TROPESS/CrIS CO profiles and error characterization for continuing the multi-decadal record of satellite CO observations.

Hourly biomass burning emissions product from blended geostationary and polar-orbiting satellites for air quality forecasting applications

Biomass burning influences atmospheric composition and regional air quality. The hourly biomass-burning emissions are usually required by air quality models, yet most available emission inventories provide daily or monthly estimates in 0.1° or coarser grids, limiting the prediction accuracy. The Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellites – R Series (GOES-R) observes fires across the conterminous United States (CONUS) every 5 min at a spatial resolution of 2 km, which allows for characterizing fires and emissions on diurnal scale. In this study, we developed a new operational algorithm to generate regional hourly 3 km fire emission across the CONUS by fusing temporally resolved ABI fire radiative power (FRP) and fine spatial-resolution (375 m) FRP from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Joint Polar Satellite System (JPSS) satellites. To do this, ABI FRP was first calibrated against and fused with VIIRS FRP in 3 km grids. Then, FRP diurnal cycles at an interval of 5 min were reconstructed using the fused ABI-VIIRS FRP and the land cover-ecoregion-specific FRP diurnal climatologies. The reconstructed FRP diurnal cycles were applied to estimate hourly emissions of eight species (e.g., carbon monoxide (CO) and fine particulate matter with diameters <2.5 μm (PM2.5)). The accuracy was verified by comparing with CO observations from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel-5 Precursor satellite, and with PM2.5 emissions from eight other inventories. The results of the ABI-VIIRS estimates during one year from April 2020 to March 2021 indicate that fires burned 221 Tg dry matter and emit 2.25 Tg PM2.5 emissions across the CONUS. The seasonal and diurnal patterns of emissions vary with land cover types. The largest and smallest seasonal variations are shown in forest and agriculture fire emissions, respectively. The diurnal emission patterns of different land cover types share similar shapes but differ largely in magnitude. Moreover, the diurnal pattern of forest fire emissions suggests that emissions are dominated during daytime in the eastern U.S. but strong during both daytime and nighttime in the western U.S. The evaluation shows that the fused ABI-VIIRS based CO agrees well with the TROPOMI CO, with a difference of 11%. However, the agreement between fused ABI-VIIRS emissions and other inventories varies for different fire events.

Analysis of source distribution of high carbon monoxide events using airborne and surface observations in Korea

Carbon monoxide (CO) is a key tracer of anthropogenic pollution, and it indirectly affects climate change. Anmyeon-do (AMY, 36.54° N, 126.33° E), a World Meteorological Organization/Global Atmosphere Watch Program (WMO/GAW) regional background station in Korea, provides continuous observations of CO mole fractions at the surface and vertical profiles within 0.5–9 km that are also collected by aircraft campaigns. The vertical profiles collected in 2019 were analyzed using meteorological parameters such as vertical velocity and boundary layer height (BLH), and a strong relationship was observed among them; however, the vertical distribution, which was influenced by unexpected strong pollution plumes, did not exhibit a strong relationship with vertical velocity and BLH. On November 16, we captured a strong CO signal within the boundary layer and at approximately 2 km above the BLH, where vertical profiles of the aerosol scattering coefficient at 550 nm were simultaneously observed with the same vertical structure. To identify the origins and source types of the stratification of the pollution plume for CO and aerosol, we also analyzed surface in situ observations of particle size distributions and reactive gases (NOx, O3, and SO2) as well as the column averaged dry-air mole fraction of carbon monoxide (XCO) and measurements of aerosol optical depth obtained from the tropospheric monitoring instrument (TROPOMI) and moderate resolution imaging spectroradiometer (MODIS) satellite, respectively. The high CO event within the BLH, including observations at the surface site, was attributed to domestic burning sources. Convective uplifting of industrial fossil fuel emissions from eastern China was responsible for the high CO dry mole fraction in the low free troposphere (FT) and the elevated aerosol scattering coefficient. Statistical analyses of one-year surface in situ observations of CO reveal that CO-emission sources from eastern China contributed to extremely high CO spikes (≥80th percentile of CO or ≥ 350 ppb, approximately) in 2019. Therefore, we concluded that emissions from eastern China have a potentially leading role in the observed high pollution events at the surface and the lower FT over the AMY station in 2019. The increase in ground temperature, with the acceleration of the global warming process, can intensify the convective uplifting of pollution plumes from emission source regions to FT over East Asian regions. In addition, such an occurrence of the stratification of the atmospheric pollution plume in the troposphere should be considered in future studies on radiative forcing to improve air-quality forecasting in this region.

COMAP Early Science. V. Constraints and Forecasts at z ∼ 3

We present the current state of models for the z ∼ 3 carbon monoxide (CO) line intensity signal targeted by the CO Mapping Array Project (COMAP) Pathfinder in the context of its early science results. Our fiducial model, relating dark matter halo properties to CO luminosities, informs parameter priors with empirical models of the galaxy–halo connection and previous CO (1–0) observations. The Pathfinder early science data spanning wavenumbers k = 0.051–0.62 Mpc−1 represent the first direct 3D constraint on the clustering component of the CO (1–0) power spectrum. Our 95% upper limit on the redshift-space clustering amplitude A clust ≲ 70 μK2 greatly improves on the indirect upper limit of 420 μK2 reported from the CO Power Spectrum Survey (COPSS) measurement at k ∼ 1 Mpc−1. The COMAP limit excludes a subset of models from previous literature and constrains interpretation of the COPSS results, demonstrating the complementary nature of COMAP and interferometric CO surveys. Using line bias expectations from our priors, we also constrain the squared mean line intensity–bias product, ≲ 50 μK2, and the cosmic molecular gas density, ρ H2 < 2.5 × 108 M ⊙ Mpc−3 (95% upper limits). Based on early instrument performance and our current CO signal estimates, we forecast that the 5 yr Pathfinder campaign will detect the CO power spectrum with overall signal-to-noise ratio of 9–17. Between then and now, we also expect to detect the CO–galaxy cross-spectrum using overlapping galaxy survey data, enabling enhanced inferences of cosmic star formation and galaxy evolution history.

Discrepancy in assimilated atmospheric CO over East Asia in 2015–2020 by assimilating satellite and surface CO measurements

Abstract. Satellite and surface carbon monoxide (CO) observations have been widely used to investigate the sources and variabilities of atmospheric CO. However, comparative analyses to explore the effects of satellite and surface measurements on atmospheric CO assimilations are still lacking. Here we investigate the assimilated atmospheric CO over East Asia in 2015–2020, via assimilating CO measurements from the Measurement of Pollution in the Troposphere (MOPITT) instrument and Ministry of Ecology and Environment of China (MEE) monitoring network. We find noticeable inconsistencies in the assimilations: the adjusted CO columns (Xco) are about 162, 173 and 172 ppb by assimilating surface CO measurements, in contrast to 138–144, 149–155 and 144–151 ppb by assimilating MOPITT CO observations over East China, the North China Plain (NCP), and the Yangtze River Delta (YRD), respectively. These inconsistencies could be associated with possible representation errors due to differences between urban and regional CO backgrounds. Furthermore, the adjusted surface CO concentrations are about 631, 806, and 657 ppb by assimilating surface CO measurements, in contrast to 418–427, 627–639 and 500–509 ppb by assimilating MOPITT CO observations over East China, NCP, and YRD, respectively; assimilations of normalized surface CO measurements (to mitigate the influences of representation errors) indicate declines of CO columns by about 2.2, 2.1, and 1.8 ppb yr−1, in contrast to 0.63–0.86, 0.97–1.29, and 1.0–1.27 ppb yr−1 by assimilating MOPITT CO measurements over East China, South Korea, and Japan, respectively. These discrepancies reflect the different vertical sensitivities of satellite and surface observations in the lower and free troposphere. This work demonstrates the importance of integrating information from satellite and surface measurements to provide a more accurate evaluation of atmospheric CO changes.