Carbon Monoxide Column Densities Research Articles

Updated Inventory of Carbon Monoxide in the Taurus Molecular Cloud

The most extensive survey of carbon monoxide (CO) gas in the Taurus molecular cloud relied on 12CO and 13CO J = 1 → 0 emission only, distinguishing the region where 12CO is detected without 13CO (named mask 1 region) from the one where both are detected (mask 2 region) (Goldsmith et al. ; Pineda et al. ). We have taken advantage of recent 12CO J = 3 → 2 James Clerk Maxwell Telescope observations, where they include mask 1 regions to estimate density, temperature, and N(CO) with a large velocity gradient model. This represents 1395 pixels out of ∼1.2 million in the mark 1 region. Compared to Pineda et al. () results and assuming a T kin of 30 K, we find a higher volume density of molecular hydrogen of 3.3 × 103 cm−3, compared to their 250–700 cm−3, and a CO column density of 5.7 × 1015 cm−2, about a quarter of their value. The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium. Future observations to extend the 12CO J = 3 → 2 mapping further away from the 13CO-detected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.

Estimation of biomass burning emission of NO2 and CO from 2019–2020 Australia fires based on satellite observations

Abstract. The bushfires that occurred in Australia in late 2019 and early 2020 were unprecedented in terms of their scale, intensity, and impacts. Using nitrogen dioxide (NO2) and carbon monoxide (CO) data measured by the Tropospheric Monitoring Instrument (TROPOMI), together with fire counts and fire radiative power (FRP) from MODIS, we analyzed the temporal and spatial variation of NO2 and CO column densities over three selected areas covering savanna and temperate forest vegetation. The ΔNO2/ΔCO emission ratio and emission factor were also estimated. The ΔNO2/ΔCO emission ratio was found to be 1.57 ± 1.71 for temperate forest fire and ranged from 2.0 ± 2.36 to 2.6 ± 1.92 for savanna fire. For savanna and temperate forest fires, satellite-derived NOx emission factors were found to be 1.48 and 2.39 g kg−1, respectively, whereas the CO emission factors are 107.39 and 126.32 g kg−1, respectively. This study demonstrates that the large-scale emission ratio from the TROPOMI satellite for different biomass burnings can help identify the relative contribution of smoldering and flaming activities in a large region and their impacts on the regional atmospheric composition and air quality. This method can be applied to study the emissions from other large fires, or even the burning of fossil fuel in megacities, and their impact on air quality.

Spatiotemporal variability/stability analysis of NO2, CO, and land surface temperature (LST) during COVID-19 lockdown in Amman city, Jordan

ABSTRACT The massive lockdown of human socioeconomic activities and vehicle movements due to the COVID-19 pandemic in 2020 has resulted in an unprecedented reduction in pollutant gases such as Nitrogen Dioxide (NO2) and Carbon Monoxide (CO) as well as Land Surface Temperature (LST) in Amman as well as all countries around the globe. In this study, the spatial and temporal variability/stability of NO2, CO, and LST throughout the lockdown period over Amman city have been analyzed. The NO2 and CO column density values were acquired from Sentinel-5p while the LST data were obtained from MODIS satellite during the lockdown period from 20 March to 24 April in 2019, 2020, and 2021. The statistical analysis showed an overall reduction in NO2 in 2020 by around 27% and 48% compared to 2019 and 2021, respectively. However, an increase of 7% in 2021 compared to 2019 was observed because almost all anthropogenic activities were allowed during the daytime. The temporal persistence showed almost constant NO2 values in 2020 over the study area throughout the lockdown period. In addition, a slight decrease in CO (around 1%) was recorded in 2020 and 2021 compared to the same period in 2019. Restrictions on human activities resulted in an evident drop in LST in 2020 by around 13% and 18% less than the 5-year average and 2021 respectively. The study concludes that due to the restrictions imposed on industrial activities and automobile movements in Amman city, an unprecedented reduction in NO2, CO, and LST was recorded.

Ultraviolet HST Spectroscopy of Planck Cold Clumps

Abstract We report results of the first study utilizing the ultraviolet capabilities of the Hubble Space Telescope to investigate a sample of Planck Galactic Cold Clump (PGCC) sources. We have selected high-resolution spectra toward 25 stars that contain a multitude of interstellar absorption lines associated with the interstellar medium (ISM) gas within these PGCC sources, including carbon monoxide (CO), C i and O i. By building cloud-component models of the individual absorption components present in these spectra, we can identify and isolate components associated with the PGCC sources, allowing for a more accurate investigation of the ISM behavior within these sources. Despite probing a broad range of overall sightline properties, we detect CO along each sightline. Sightlines with CO column density N(CO) > 1015 cm−2 exhibit spatial dependence in N(CO) and CO/C i, while sightlines with N(CO) < 1015 cm−2 show no such spatial dependence. Differences between N(H2) values derived from UV absorption and dust emission suggest structure in the spatial distribution of N(H2), where “CO-bright” sightlines are associated with PGCC sources embedded within smooth translucent envelopes, and “CO-dark” sightlines are associated with PGCC sources embedded in patchier environments containing more diffuse gas.

THE FAR-ULTRAVIOLET “CONTINUUM” IN PROTOPLANETARY DISK SYSTEMS. II. CARBON MONOXIDE FOURTH POSITIVE EMISSION AND ABSORPTION*

ABSTRACT We exploit the high sensitivity and moderate spectral resolution of the Hubble Space Telescope Cosmic Origins Spectrograph to detect far-ultraviolet (UV) spectral features of carbon monoxide (CO) present in the inner regions of protoplanetary disks for the first time. We present spectra of the classical T Tauri stars HN Tau, RECX-11, and V4046 Sgr, representative of a range of CO radiative processes. HN Tau shows CO bands in absorption against the accretion continuum. The CO absorption most likely arises in warm inner disk gas. We measure a CO column density and rotational excitation temperature of N(CO) = (2 ± 1) × 1017 cm−2 and T rot(CO) 500 ± 200 K for the absorbing gas. We also detect CO A–X band emission in RECX-11 and V4046 Sgr, excited by UV line photons, predominantly H i Lyα. All three objects show emission from CO bands at λ > 1560 Å, which may be excited by a combination of UV photons and collisions with non-thermal electrons. In previous observations these emission processes were not accounted for due to blending with emission from the accretion shock, collisionally excited H2, and photo-excited H2, all of which appeared as a “continuum” whose components could not be separated. The CO emission spectrum is strongly dependent upon the shape of the incident stellar Lyα emission profile. We find CO parameters in the range: N(CO) ∼ 1018–1019 cm−2, T rot(CO) ≳ 300 K for the Lyα-pumped emission. We combine these results with recent work on photo-excited and collisionally excited H2 emission, concluding that the observations of UV-emitting CO and H2 are consistent with a common spatial origin. We suggest that the CO/H2 ratio (≡ N(CO)/N(H2)) in the inner disk is ∼1, a transition between the much lower interstellar value and the higher value observed in solar system comets today, a result that will require future observational and theoretical study to confirm.

Modelling CO emission - I. CO as a column density tracer and the X factor in molecular clouds

Theoretical and observational investigations have indicated that the abundance of carbon monoxide (CO) is very sensitive to intrinsic properties of the gaseous medium, such as density, metallicity, and the background UV field. In order to accurately interpret CO observations, it is thus important to understand how well CO traces the gas, which in molecular clouds (MCs) is predominantly molecular hydrogen (H2). Recent hydrodynamic simulations by Glover & Mac Low have explicitly followed the formation and destruction of molecules in model MCs under varying conditions, confirming that CO formation strongly depends on the cloud properties. Conversely, the H2 formation is primarily determined by the age of the MC. We apply radiative transfer calculations to these MC models in order to investigate the properties of CO line emission. We focus on integrated CO (J=1-0) intensities emerging from individual clouds, including its relationship to the total, H2, and CO column densities, as well as the "X factor," the ratio of H2 column density to CO intensity. Models with high CO abundances have a threshold CO intensity ~65 K km/s at sufficiently large extinctions. Clouds with low CO abundances show no such intensity thresholds. The distribution of H2 column densities are well described as log-normal functions, though the distributions of CO intensities and column densities are usually not log-normal. In general, the PDFs of the integrated intensity do not follow the distribution functions of CO column densities. In the model with Milky Way-like conditions, the X factor is in agreement with the near constant value determined from observations. In clouds with lower CO abundances the X factor can vary appreciably - sometimes by > 4 orders of magnitude. In models with high densities, the CO line is fully saturated, so that the X factor is directly proportional to the molecular column density.

ACCURATE LABORATORY WAVELENGTHS OF THE e 3 Σ – (ν′ = 5) – X 1 Σ + (ν″ = 0) BAND OF 12 C 16 O

The forbidden singlet-triplet transitions of carbon monoxide (CO) are important in the interpretation of vacuum ultraviolet interstellar absorption spectra and in particular for the measurement of large CO column densities. Twenty rovibronic lines of the e 3Σ–(ν' = 5) – X 1Σ+(ν'' = 0) band of 12 C 16O for which laboratory wavelengths were previously unavailable were identified in laser-induced fluorescence excitation spectra. Wavelengths were assigned to five rovibronic transitions to an average accuracy of 0.0028 A. A further 15 lines could not be fully resolved and average wavelengths were measured for these groups of closely spaced lines. A wavelength difference of 0.011 ± 0.0028 A between the measured wavelengths and the calculated wavelengths in the atlas of Eidelsberg & Rostas demonstrates the need for more experimental data on CO.

Tropospheric carbon monoxide column density retrieval during Pre-launch MOPITT Validation exercise

The tropospheric carbon monoxide (CO) column density over the United States Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SGP) Central Facility near Lamont, Oklahoma (latitude 36°37′N, longitude 97°30′W) during the Pre-launch MOPITT Validation Exercise (Pre-MOVE) is retrieved from infrared spectra obtained by the ground-based Atmospheric Emitted Radiance Interferometer (AERI). This paper reports the first tropospheric CO time series retrieved from an AERI. With spectra measured every 8 min, CO retrieved from AERI spectra has a much higher temporal resolution than from any other ground-based instrument measuring atmospheric emission. The retrieved CO column density time series is examined using local meteorological data. Synoptic atmospheric conditions are found to have a controlling effect on tropospheric CO. During 2–4 March, 1998, a southerly to easterly surface wind brought an airmass with higher CO column density over the SGP Central Facility (SGPCF), whereas northerly and/or westerly surface winds tended to reduce the CO column density.

Physical State of Molecular Gas in High Galactic Latitude Translucent Clouds

The rotational transitions of carbon monoxide (CO) are the primary means of investigating the density and velocity structure of the molecular interstellar medium. Here we study the lowest four rotational transitions of CO toward high-latitude translucent molecular clouds (HLCs). We report new observations of the J = (4-3), (2-1), and (1-0) transitions of CO toward eight high-latitude clouds. The new observations are combined with data from the literature to show that the emission from all observed CO transitions is linearly correlated. This implies that the excitation conditions that lead to emission in these transitions are uniform throughout the clouds. Observed 13CO/12CO (1-0) integrated intensity ratios are generally much greater than the expected abundance ratio of the two species, indicating that the regions that emit 12CO (1-0) radiation are optically thick. We develop a statistical method to compare the observed line ratios with models of CO excitation and radiative transfer. This enables us to determine the most likely portion of the physical parameter space that is compatible with the observations. The model enables us to rule out CO gas temperatures greater than ~30 K, since the most likely high-temperature configurations are 1 pc-sized structures aligned along the line of sight. The most probable solution is a high-density and low-temperature (HDLT) solution, with volume density, n = 104.5±0.5 cm-3, kinetic temperature, Tk ≈ 8 K, and CO column density per velocity interval NCO/ΔV = 1016.6±0.3 cm-2/( km s-1). The CO cell size is L ~ 0.01 pc (~2000 AU). These cells are thus tiny fragments within the ~100 times larger CO-emitting extent of a typical high-latitude cloud. We discuss the physical implications of HDLT cells, and we suggest ways to test for their existence.

Remote sensing of carbon monoxide over the continental United States on September 12–13, 1993

Tropospheric carbon monoxide (CO) column densities were retrieved from 491 nadir infrared spectra obtained by the University of Wisconsin's High‐Resolution Interferometer Sounder (HIS) during a cross‐country flight of a NASA ER‐2 on September 12–13, 1993 (UT). A classical, Fourier‐based signal‐processing technique was utilized to retrieve the CO column density from the 2135–2200 cm−1 portion of the CO 1–0 vibration‐rotation band. Error analysis indicates column CO retrieval uncertainties of approximately ±10%. Retrieved CO column densities over the western United States from this flight, ∼1.2×1018 cm−2, agree well with previous ground‐based CO column measurements over the western United States at the same season. Derived CO sensitivity functions for these measurements possess a broad peak centered in the 500–600 mbar region, thus implying the retrieved tropospheric CO mixing ratios are indicative of the mean free troposphere (mft). Across the United States, three spatial groupings of CO were observed: west, mft CO ∼76 parts per billion by volume (ppbv); midwest, mft CO ∼56 ppbv; and east, mft CO ∼71 ppbv. Weather map and back trajectory analyses indicate different source regions for the air parcels in each of these regions. The low CO amounts over the midwest most likely result from the mixing of rapidly subsiding air naturally low in CO with a low‐altitude inflow of similarly clean subtropical air off the Gulf of Mexico. These results demonstrate the utility of satellite infrared spectrometer observations to globally map tropospheric CO abundances and further reveal the impact of synoptic scale atmospheric circulations on CO abundances.

The relationship between carbon monoxide abundance and visual extinction in interstellar clouds

Carbon monoxide column densities are compared to visual extinctions toward field stars in the rho Oph and Taurus molecular cloud complexes. The relationship of C(0-18) column density to extinction is established, and new determinations for (C-13)O column densities are given for a range of visual extinctions extended to beyond 20 mag. A prescription for determining hydrogen column densities and masses of molecular clouds from observations of CO isotopes is presented and discussed critically. These measurements agree well with the predictions of gas phase chemistry models which include chemical fractionation and selective isotopic photodestruction. The functional dependence of the C(O-18) column density on extinction is characterized by two different regimes separated by a distinct transition observed to occur at 4 mag in both molecular cloud complexes, whereas the functional dependence of (C-13)O is quite different in the two regions. Some saturation is found to occur for C(O-18) emission at high visual extinction and use the rarer isotopic species C(O-17) and (C-13)(O-18) to correct for it.