Vertical Profiles Of CO Research Articles

Assessment of WRF-CO2 simulated vertical profiles of CO2 over Delhi region using aircraft and global model data

High-resolution regional model simulation of CO2 may be more beneficial to reduce the uncertainty in estimation of CO2 source and sink via inverse modeling. However, the study of atmospheric CO2 transport with regional models is rare over India. Here, weather research and forecasting chemistry model adjusted for CO2 (WRF-CO2) is used for simulating vertical profile of CO2 and its assessment is performed over Delhi, India (27.4–28.6° N and 77–96° E) by comparing aircraft observations (CONTRAIL) and a global model (ACTM) data. During August and September, the positive vertical gradient (~ 13.4 ppm) within ~ 2.5 km height is observed due to strong CO2 uptake by newly growing vegetation. A similar pattern (~ 4 ppm) is noticed in February due to photosynthesis by newly growing winter crops. The WRF-CO2 does not show such steep increasing slope (capture up to 5%) during August and September but same for February is estimated ~ 1.7 ppm. Generally, CO2 is quite well mixed between ~ 2.5 and ~ 8 km height above ground which is well simulated by the WRF-CO2 model. During stubble burning period of 2010, the highest gradient within 2.5 km height above ground was recorded in October (− 9.3 ppm), followed by November (− 7.6 ppm). The WRF-CO2 and ACTM models partially capture these gradients (October − 3.3 and − 2.7 ppm and November − 3.8 and − 4.3 ppm respectively). A study of the seasonal variability of CO2 indicates seasonal amplitudes decrease with increasing height (amplitude is ~ 21 ppm at the near ground and ~ 6 ppm at 6–8 km altitude bin). Correlation coefficients (CC) between the WRF-CO2 model and observation are noted to be greater than 0.59 for all the altitude bins. In contrast to simulated fossil CO2, the biospheric CO2 is in phase with observed seasonality, having about 80% at the lowest level and gradually declines with height due to mixing processes, reaching around 60% at the highest level. The model simulation reveals that meteorology plays a significant role of the horizontal and vertical gradient of CO2 over the region.

Three-dimensional spatiotemporal variability of CO2 in suburban and urban areas of Shaoxing City in the Yangtze River Delta, China

Metropolitan areas are the most anthropogenically active places but there is a lack of knowledge in carbon dioxide (CO2) spatial distribution in suburban and urban areas. In this study, the CO2 three-dimensional distributions were obtained from 92 times vertical unmanned aerial vehicle (UAV) flight observations in Shaoxing suburbs and 90 times ground mobile observations in Shaoxing urban areas from Nov. 2021 to Nov. 2022. The vertical distribution showed that CO2 concentrations gradually decreased from 450 to 420 ppm with altitude from 0 to 500 m. CO2 vertical profile concentrations can be influenced by transport from multiple regions. Based on the vertical observation data combining a potential source contribution function (PSCF) model, Shaoxing suburban CO2 were to be derived from urban areas in spring and autumn, while in winter and autumn were mainly from the long-transports from neighboring cities. Further the CO2 concentrations of urban horizontal distribution were observed in the range of 460–510 ppm through the mobile campaigns. Urban CO2 were partly emitted from traffic exhausts and residential combustion. Overall, CO2 concentrations were observed to be lower in spring and summer due to the CO2 uptake by plant photosynthesis. This uptake was initially quantified and accounted for 4.2 % of total CO2 in suburbs and 3.3 % in urban areas by calculating the decrease in CO2 concentration from peak to trough in the daytime. Compared with the CO2 observed in the Lin'an background station, the maximum regional CO2 enhancement in Shaoxing urban areas reached to 8.9 % while the maximum in suburbs only 4.4 %. The contribution differences between urban and suburban areas to regional CO2 were relatively constant at 1.6 % in four seasons may be mainly ascribed to the contribution of long-range CO2 transport to the suburbs.

Retrieval of Martian Atmospheric CO Vertical Profiles From NOMAD Observations During the First Year of TGO Operations

AbstractWe present CO density profiles up to about 100 km in the Martian atmosphere obtained for the first time from retrievals of solar occultation measurements by the Nadir and Occultation for Mars Discovery (NOMAD) onboard ExoMars Trace Gas Orbiter (TGO). CO is an important trace gas on Mars, as it is controlled by CO2 photolysis, chemical reaction with the OH radicals, and the global dynamics. However, the measurements of CO vertical profiles have been elusive until the arrival of TGO. We show how the NOMAD CO variations describe very well the Mars general circulation. We observe a depletion of CO in the upper troposphere and mesosphere during the peak period, LS = 190°–200°, more pronounced over the northern latitudes, confirming a similar result recently reported by Atmospheric Chemistry Suite onboard TGO. However, in the lower troposphere around 20 km, and at least at high latitudes of the S. hemisphere, NOMAD CO mixing ratios increase over 1,500 ppmv during the GDS (Global Dust Storm) onset. This might be related to the downwelling branch of the Hadley circulation. A subsequent increase in tropospheric CO is observed during the decay phase of the GDS around LS = 210°–250° when the dust loading is still high. This could be associated with a reduction in the amount of OH radicals in the lower atmosphere due to lack of solar insolation. Once the GDS is over, CO steadily decreases globally during the southern summer season. A couple of distinct CO patterns associated with the Summer solstice and equinox circulation are reported and discussed.

RESTORING THE CO2 CONCENTRATION ON IR–SPECTRA OF THE SOLAR LIGHT TRANSMISSION THROUGH THE ATMOSPHERE BY THE MODIFIED GAUSS–NEWTON METHOD

The inverse problem of reconstructing the vertical profiles of CO2 in the atmo- sphere by IR–spectra of the solar light transmission is investigated. To solve this problem, we propose the two-stage method. On the first stage, we use the modified Tikhonov method. On the second stage, to approximate a solution of the regularized equation, we apply the modified Gauss–Newton method. The convergence theorem is formulated and the numerical results for a few of measured spectra are presented.

UAV-based sampling systems to analyse greenhouse gases and volatile organic compounds encompassing compound-specific stable isotope analysis

Abstract. The study herein reports on the development and testing of sampling systems (and subsequent analytical setups) that were deployed on an unmanned aerial vehicle (UAV) for the purpose of analysing greenhouse gases (GHGs) and volatile organic compounds (VOCs) in the lower atmospheric boundary layer. Two sampling devices, both of which can be mounted to an UAV with a payload capability greater than 1 kg, were tested for respective sampling and analysis of specific GHGs (carbon dioxide, CO2, and methane, CH4) and VOCs (chlorinated ethenes, CEs). The gas analyses included measurements of the molar amounts and the respective stable carbon isotope ratios. In addition to compound calibration in the laboratory, the functionality of the samplers and the UAV-based sampling was tested in the field. Atmospheric air was either flushed through sorbent tubes for VOC sampling or collected and sampled in glass vials for GHG analysis. The measurement setup for the sorbent tubes achieved analyte mass recovery rates of 63 %–100 % (more favourable for lower chlorinated ethenes), when prepared from gaseous or liquid calibration standards, and reached a precision (2σ) better than 0.7 ‰ for δ13C values in the range of 0.35–4.45 nmol. The UAV-equipped samplers were tested over two field sampling campaigns designed to (1) compare manual and UAV-collected samples taken up a vertical profile at a forest site and (2) identify potential emissions of CO2, CH4 or VOC from a former domestic waste dump. The precision of CO2 measurements from whole air samples was ≤7.3 µmol mol−1 and ≤0.3 ‰ for δ13C values and ≤0.03 µmol mol−1 and ≤0.2 ‰ for CH4 working gas standards. The results of the whole air sample analyses for CO2 and CH4 were sufficiently accurate to detect and localise potential landfill gas emissions from a secured former domestic waste dump using level flight. Vertical CO2 profiles from a forest location showed a causally comprehensive pattern in the molar ratios and stable carbon isotope ratios but also the potential falsification of the positional accuracy of a UAV-assisted air sample due to the influence of the rotor downwash. The results demonstrate that the UAV sampling systems presented here represent a viable tool for atmospheric background monitoring, as well as for evaluating and identifying emission sources. By expanding the part of the lower atmosphere that can be practicably sampled over horizontal and vertical axes, the presented UAV-capable sampling systems, which also allow for compound-specific stable isotope analysis (CSIA), may facilitate an improved understanding of surface–atmosphere fluxes of trace gas.

Retrieval of Martian atmospheric CO vertical profiles from NOMAD observations during the 1st year of TGO operations

Retrieval of Martian atmospheric CO vertical profiles from NOMAD observations during the 1st year of TGO operations

Monitoring of Atmospheric Carbon Dioxide over a Desert Site Using Airborne and Ground Measurements

Accurate monitoring of atmospheric carbon dioxide (CO2) is of great significance for studying the carbon cycle. Compared to ground observational sites, airborne observations cover a wider area, which help in effectively monitoring the distribution of CO2 sources and sinks. In this study, an airborne campaign was carried out in June and July 2021 to measure the atmospheric CO2 concentration over a desert site, Dunhuang, located in western China. The dry-air column-averaged CO2 mole fraction (XCO2) inversion results obtained from the Atmospheric Carbon Dioxide Lidar (ACDL) system were compared with the Orbiting Carbon Observatory 2 (OCO-2) retrievals, portable Fourier Transform Spectrometer (EM27/SUN) measurement results, and with the XCO2 estimates derived using the airborne Ultraportable Greenhouse Gas Analyzer (UGGA) and the Copernicus Atmosphere Monitoring Service (CAMS) model measurements. Moreover, the vertical CO2 profiles obtained from the OCO-2 and the CAMS datasets were also compared with the airborne UGGA measurements. OCO-2 and CAMS CO2 measurements showed a vertical distribution pattern similar to that of the aircraft-based measurements of atmospheric CO2. In addition, the relationship of atmospheric CO2 with the aerosol optical depth (AOD) was also determined and the results showed a strong and positive correlation between the two variables.

Analysis of four solar occultations by Titan’s atmosphere with the infrared channel of the VIMS instrument: Haze, CH4, CH3D, and CO vertical profiles

Titan, the largest satellite of Saturn, has a dense atmosphere mainly composed of nitrogen, methane at a percent level, and minor species. It is also covered by a thick and global photochemical organic haze. In the last two decades, the observations made by the Cassini orbiter and the Huygens probe have greatly improved our knowledge of Titan's system. The surface, haze, clouds, and chemical species can be studied and characterised with several instruments simultaneously. On the other hand, some compounds of its climatic cycle remain poorly known. This is clearly the case of the methane cycle, which is, however, a critical component of Titan's climate and of its evolution. We reanalysed four solar occultations by Titan's atmosphere observed with the infrared part of the Visual Infrared Mapping Spectrometer (VIMS) instrument. These observations were already analysed, but here we used significantly improved methane spectroscopic data. We retrieved the haze properties (not treated previously) and the mixing ratios of methane, deuterated methane, and CO in the stratosphere and in the low mesosphere. The methane mixing ratio in the stratosphere is much lower (about 1.1%) than expected from Huygens measurements (about 1.4 to 1.5%). This is consistent with previous results obtained with other instruments. However, features in the methane vertical profiles clearly demonstrate that there are interactions between the methane distribution and the atmosphere circulation. We also retrieved the haze extinction profiles and the haze spectral behaviour. We find that aerosols are aggregates with a fractal dimension of Df ≃ 2.3 ± 0.1, rather than Df ≃ 2 as previously thought. Our analysis also reveals noticeable changes in their size distribution and their morphology with altitude and time. These changes are also clearly connected to the atmosphere circulation and concerns the whole stratosphere and the transition between the main and the detached haze layers. We finally display the vertical profiles of CH3D and CO for the four observations. Although the latter retrievals have large error bars due to noisy data, we could derive values in agreement with other works.

Exploring the variability of the venusian thermosphere with the IPSL Venus GCM

Recent simulations of the Institut Pierre-Simon Laplace (IPSL) Venus Global Climate Model (VGCM) developed at the Laboratoire de Météorologie Dynamique (LMD) were performed with a model top raised from ∼10−5 (∼150 km) to ∼10−8 Pa (180–250 km; upper boundary). The parameterizations of non-LTE CO2 near infrared heating rates and of non-orographic gravity waves were improved. In addition, a tuning of atomic oxygen production was introduced to improve related effects (heating and cooling) and resulting thermospheric number densities. This work focusses on validating the modelled thermospheric structure using data from the Pioneer Venus, Magellan and Venus Express missions which cover similar and complementary (equator and pole) regions at different periods of solar activity, typically above altitudes of 130 km. This version of the IPSL VGCM shows good agreement with the diurnal evolution of the exospheric temperature at the equator reconstructed from the atomic oxygen scale height of the Pioneer Venus Orbiter Neutral Mass Spectrometer data. The model is also able to reproduce the sensitivity of the exospheric temperature and species density to the EUV flux of the solar high activity period (from 180 to 230 solar flux unit; s.f.u). However, to fit with the PV-ONMS density observations, it was necessary to increase the photodissociation of CO2 into CO and O above 135 km by a factor of 10. Indeed, our study points to the importance of an additional source of oxygen and carbon monoxide production above 130 km other than CO2 photolysis to explain the vertical profiles of CO and O number density in the thermosphere. Moreover, the presence of a GW drag at altitudes above 140 km has a significant impact on the nightside temperature value and its distribution.

A 10-year global monthly averaged terrestrial net ecosystem exchange dataset inferred from the ACOS GOSAT v9 XCO2 retrievals (GCAS2021)

Abstract. A global gridded net ecosystem exchange (NEE) of CO2 dataset is vital in global and regional carbon cycle studies. Top-down atmospheric inversion is one of the major methods to estimate the global NEE; however, the existing global NEE datasets generated through inversion from conventional CO2 observations have large uncertainties in places where observational data are sparse. Here, by assimilating the GOSAT ACOS v9 XCO2 product, we generate a 10-year (2010–2019) global monthly terrestrial NEE dataset using the Global Carbon Assimilation System, version 2 (GCASv2), which is named GCAS2021. It includes gridded (1∘×1∘), globally, latitudinally, and regionally aggregated prior and posterior NEE and ocean (OCN) fluxes and prescribed wildfire (FIRE) and fossil fuel and cement (FFC) carbon emissions. Globally, the decadal mean NEE is -3.73±0.52 PgC yr−1, with an interannual amplitude of 2.73 PgC yr−1. Combining the OCN flux and FIRE and FFC emissions, the net biosphere flux (NBE) and atmospheric growth rate (AGR) as well as their inter-annual variabilities (IAVs) agree well with the estimates of the Global Carbon Budget 2020. Regionally, our dataset shows that eastern North America, the Amazon, the Congo Basin, Europe, boreal forests, southern China, and Southeast Asia are carbon sinks, while the western United States, African grasslands, Brazilian plateaus, and parts of South Asia are carbon sources. In the TRANSCOM land regions, the NBEs of temperate N. America, northern Africa, and boreal Asia are between the estimates of CMS-Flux NBE 2020 and CT2019B, and those in temperate Asia, Europe, and Southeast Asia are consistent with CMS-Flux NBE 2020 but significantly different from CT2019B. In the RECCAP2 regions, except for Africa and South Asia, the NBEs are comparable with the latest bottom-up estimate of Ciais et al. (2021). Compared with previous studies, the IAVs and seasonal cycles of NEE of this dataset could clearly reflect the impacts of extreme climates and large-scale climate anomalies on the carbon flux. The evaluations also show that the posterior CO2 concentrations at remote sites and on a regional scale, as well as on vertical CO2 profiles in the Asia-Pacific region, are all consistent with independent CO2 measurements from surface flask and aircraft CO2 observations, indicating that this dataset captures surface carbon fluxes well. We believe that this dataset can contribute to regional- or national-scale carbon cycle and carbon neutrality assessment and carbon dynamics research. The dataset can be accessed at https://doi.org/10.5281/zenodo.5829774 (Jiang, 2022).

Validation of GOSAT and OCO-2 against In Situ Aircraft Measurements and Comparison with CarbonTracker and GEOS-Chem over Qinhuangdao, China

Carbon dioxide (CO2) is the most important greenhouse gas and several satellites have been launched to monitor the atmospheric CO2 at regional and global scales. Evaluation of the measurements obtained from these satellites against accurate and precise instruments is crucial. In this work, aircraft measurements of CO2 were carried out over Qinhuangdao, China (39.9354°N, 119.6005°E), on 14, 16, and 19 March 2019 to validate the Greenhous gases Observing SATellite (GOSAT) and the Orbiting Carbon Observatory 2 (OCO-2) CO2 retrievals. The airborne in situ instruments were mounted on a research aircraft and the measurements were carried out between the altitudes of ~0.5 and 8.0 km to obtain the vertical profiles of CO2. The profiles captured a decrease in CO2 concentration from the surface to maximum altitude. Moreover, the vertical profiles from GEOS-Chem and the National Oceanic and Atmospheric Administration (NOAA) CarbonTracker were also compared with in situ and satellite datasets. The satellite and the model datasets captured the vertical structure of CO2 when compared with in situ measurements, which showed good agreement among the datasets. The dry-air column-averaged CO2 mole fractions (XCO2) retrieved from OCO-2 and GOSAT showed biases of 1.33 ppm (0.32%) and −1.70 ppm (−0.41%), respectively, relative to the XCO2 derived from in situ measurements.

Regional‐Scale, Sector‐Specific Evaluation of Global CO2 Inversion Models Using Aircraft Data From the ACT‐America Project

AbstractWe use 148 airborne vertical profiles of CO2 for frontal cases from the summer 2016 Atmospheric Carbon and Transport—America (ACT‐America) campaign to evaluate the skill of 10 global CO2 in situ inversion models from the version 7 Orbiting Carbon Observatory–2 (OCO‐2) Model Intercomparison Project (MIP). Model errors (model posterior—observed CO2 dry air mole fractions) were categorized by region (Mid‐Atlantic, Midwest, and South), frontal sector (warm or cold), and transport model (predominantly Tracer Model 5 (TM5) and Goddard Earth Observing System—Chemistry [GEOS‐Chem]). All inversions assimilated the same CO2 observations. Overall, the median inversion profiles reproduce the general structures of the observations (enhanced/depleted low‐level CO2 in warm/cold sectors), but 1) they underestimate the magnitude of the warm/cold sector mole fraction difference, and 2) the spread among individual inversions can be quite large (>5 ppm). Uniquely in the Mid‐Atlantic, inversion biases segregated according to atmospheric transport model, where TM5 inversions biases were −3 to −4 ppm in warm sectors, while those of GEOS‐Chem were +2 to +3 ppm in cold sectors. The large spread among the mean posterior CO2 profiles is not explained by the different atmospheric transport models. These results show that the inversion systems themselves are the dominant cause of this spread, and that the aircraft campaign data are clearly able to identify these large biases. Future controlled experiments should identify which inversions best reproduce mid‐latitude CO2 mole fractions, and how inversion system components are linked to system performance.

A New Background Method for Greenhouse Gases Flux Calculation Based in Back-Trajectories Over the Amazon

The large amount of carbon stored in trees and soils of the Amazon rain forest is under pressure from land use as well as climate change. Therefore, various efforts to monitor greenhouse gas exchange between the Amazon forest and the atmosphere are now ongoing, including regular vertical profile (surface to 4.5 km) greenhouse gas measurements across the Amazon. These profile measurements can be used to calculate fluxes to and from the rain forest to the atmosphere at large spatial scales by considering the enhancement or depletion relative to the mole fraction of air entering the Amazon basin from the Atlantic, providing an important diagnostic of the state, changes and sensitivities of the forests. Previous studies have estimated greenhouse gas mole fractions of incoming air (‘background’) as a weighted mean of mole fractions measured at two background sites, Barbados (Northern Hemisphere) and Ascension (Southern hemisphere) in the Tropical Atlantic, where the weights were based on sulphur hexafluoride (SF6) measured locally (in the Amazon vertical profiles) and at the two background sites. However, this method requires the accuracy and precision of SF6 measurements to be significantly better than 0.1 parts per trillion (picomole mole−1), which is near the limit for the best SF6 measurements and assumes that there are no SF6 sources in the Amazon basin. We therefore present here an alternative method. Instead of using SF6, we use the geographical position of each air-mass back-trajectory when it intersects the limit connecting these two sites to estimate contributions from Barbados versus Ascension. We furthermore extend the approach to include an observation site further south, Cape Point, South Africa. We evaluate our method using CO2 vertical profile measurements at a coastal site in Brazil comparing with values obtained using this method where we find a high correlation (r2 = 0.77). Similarly, we obtain good agreement for CO2 background when comparing our results with those based on SF6, for the period 2010–2011 when the SF6 measurements had excellent precision and accuracy. We also found high correspondence between the methods for background values of CO, N2O and CH4. Finally, flux estimates based on our new method agree well with the CO2 flux estimates for 2010 and 2011 estimated using the SF6-based method. Together, our findings suggest that our trajectory-based method is a robust new way to derive background air concentrations for the purpose of greenhouse gas flux estimation using vertical profile data.

In situ measurement of CO<sub>2</sub> and CH<sub>4</sub> from aircraft over northeast China and comparison with OCO-2 data

Abstract. Several satellites have been launched to monitor the increasing concentrations of greenhouse gases, especially CO2 and CH4 in the atmosphere, through backscattered hyperspectral radiance in the shortwave infrared (SWIR) band. The vertical profiles of greenhouse gases and aerosols could strongly affect the results from these instruments. To investigate the effects of the vertical distribution of CO2 on the uncertainty of SWIR satellite retrieval results, we conducted observations of the vertical profiles of CO2, CH4 and aerosol particles at 0.6–7 km above sea level using a Beechcraft King Air 350ER in Jiansanjiang (46.77∘ N, 131.99∘ E), Heilongjiang Province, northeast China, on 7–12 August 2018. The profiles from this aircraft captured a decrease in CO2 from 2 km to the minimum altitude due to the absorption of vegetation at the surface in summer. CH4 measurements showed about a 0.2 ppm increase from 2.0 to 0.6 km on 10 August, which may result from emissions from the large area of paddy fields below, and a constant mole fraction between 1.951 and 1.976 ppm was recorded at 2 km and above. Comparison of CO2 profiles from a new version of the carbon cycle data assimilation system Tan-Tracker (v1), retrievals from OCO-2 and aircraft measurements was conducted. The results from OCO-2 and the assimilation model system Tan-Tracker captured the vertical structure of CO2 above 3 km, whereas below 3 km the values from OCO-2 and the Tan-Tracker model were lower than those from in situ measurements. Column-averaged CO2 volume mole fractions calculated from in situ measurements showed biases of -4.68±0.44 ppm (-1.18±0.11%) compared to OCO-2 retrievals.

The development of the Atmospheric Measurements by Ultra-Light Spectrometer (AMULSE) greenhouse gas profiling system and application for satellite retrieval validation

Abstract. We report in this paper the development of an embedded ultralight spectrometer (<3 kg) based on tuneable diode laser absorption spectroscopy (with a sampling rate of 24 Hz) in the mid-infrared spectral region. This instrument is dedicated to in situ measurements of the vertical profile concentrations of three main greenhouse gases – carbon dioxide (CO2), methane (CH4) and water vapour (H2O) – via standard weather and tethered balloons. The plug and play instrument is compact, robust, cost-effective, and autonomous. The instrument also has low power consumption and is non-intrusive. It was first calibrated during an in situ experiment on an ICOS (Integrated Carbon Observation System) site for several days, then used in two experiments with several balloon flights of up to 30 km altitude in the Reims region of France in 2017–2018 in collaboration with Météo-France CNRM (Centre National de Recherches Météorologiques). This paper shows the valuable interest of the data measured by the AMULSE (Atmospheric Measurements by Ultra-Light Spectrometer) instrument during the APOGEE (Atmospheric Profiles of Greenhouse Gases) measurement experiment, specifically for the vertical profiles of CO2 and CH4, measurements of which remain very sparse. We have carried out several experiments showing that the measured profiles have several applications: the validation of simulations of infrared satellite observations, evaluating the quality of chemical profiles from chemistry transport models (CTMs) and evaluating the quality of retrieved chemical profiles from the assimilation of infrared satellite observations. The results show that the simulations of infrared satellite observations from IASI (Infrared Atmospheric Sounding Interferometer) and CrIS (Cross-track Infrared Sounder) instruments performed in operational mode for numerical weather prediction (NWP) by the radiative transfer model (RTM) RTTOV (Radiative Transfer for the TIROS Operational Vertical Sounder) are of good quality. We also show that the MOCAGE (Modèle de Chimie Atmosphérique de Grande Echelle) and CAMS (Copernicus Atmospheric Monitoring Service) CTMs modelled ozone profiles fairly accurately and that the CAMS CTM represents the methane in the troposphere well compared to MOCAGE. Finally, the measured in situ ozone profiles allowed us to show the good quality of the retrieved ozone profiles by assimilating ozone-sensitive infrared spectral radiances from the IASI and CrIS.

What supports the deep chlorophyll maximum in acidic lakes? The role of the bacterial CO2 production in the hypolimnion

AbstractThe interactions between phytoplankton, bacteria and resources, irradiance, and nutrients, leading to the formation of deep chlorophyll maxima (DCMs), are little understood in acid lakes. In “El Sancho” reservoir (Iberian Pyritic belt, Huelva, Spain), an acid mine drainage impacted waterbody (pH 3.5–4.0), a strong DCM forms in the metalimnion during the stratification period. The DCM was located always below the 1% irradiance level, where the decreasing irradiance profile overlapped with a dissolved inorganic carbon concentration (CO2) gradient decreasing upward from the hypolimnion. The DCM was dominated by the chlorophyte Carteria sp. and showed the highest volumetric photosynthetic and dark respiration rates. The DCM, however, only contributed around 20% of water column integrated gross primary production, while it accounted for 54–66% of water column chlorophyll. The total bacterial abundance correlated significantly with the CO2 concentration (r = 0.74). To test the hypothesis of a possible dependence of the formation of the DCM in acid lakes on the production of CO2 by heterotrophic bacteria, a one‐dimensional reactive transport model (DCM‐CO2) was developed and tested. The DCM‐CO2 model simulated the vertical distribution of chlorophyll (R2 > 0.63) and the vertical profile of CO2 rather accurately (R2 > 0.79), the position of DCM depending on both light penetration and an upward flux of CO2 produced by hypolimnetic heterotrophic bacteria. Overall, the results support the hypothesis of microbial degradation of organic matter being a source of CO2 for acid lake primary producers at the DCM.

Comparison of CO₂ Vertical Profiles in the Lower Troposphere between 1.6 µm Differential Absorption Lidar and Aircraft Measurements Over Tsukuba.

A 1.6 μm differential absorption Lidar (DIAL) system for measurement of vertical CO2 mixing ratio profiles has been developed. A comparison of CO2 vertical profiles measured by the DIAL system and an aircraft in situ sensor in January 2014 over the National Institute for Environmental Studies (NIES) in Tsukuba, Japan, is presented. The DIAL measurement was obtained at an altitude range of between 1.56 and 3.60 km with a vertical resolution of 236 m (below 3 km) and 590 m (above 3 km) at an average error of 1.93 ppm. An in situ sensor for cavity ring-down spectroscopy of CO2 was installed in an aircraft. CO2 mixing ratio measured by DIAL and the aircraft sensor ranged from 398.73 to 401.36 ppm and from 399.08 to 401.83 ppm, respectively, with an average difference of −0.94 ± 1.91 ppm below 3 km and −0.70 ± 1.98 ppm above 3 km between the two measurements.

Seasonal evaluation of tropospheric CO<sub>2</sub> over the Asia-Pacific region observed by the CONTRAIL commercial airliner measurements

Abstract. Measurement of atmospheric carbon dioxide (CO2) is indispensable for top-down estimation of surface CO2 sources/sinks by an atmospheric transport model. Despite the growing importance of Asia in the global carbon budget, the region has only been sparsely monitored for atmospheric CO2 and our understanding of atmospheric CO2 variations in the region (and thereby that of the regional carbon budget) is still limited. In this study, we present climatological CO2 distributions over the Asia-Pacific region obtained from the CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiner) measurements. The high-frequency in-flight CO2 measurements over 10 years reveal a clear seasonal variation in CO2 in the upper troposphere (UT), with a maximum occurring in April–May and a minimum in August–September. The CO2 mole fraction in the UT north of 40∘ N is low and highly variable in June–August due to the arrival of air parcels with seasonally low CO2 caused by the summertime biospheric uptake in boreal Eurasia. For August–September in particular, the UT CO2 is noticeably low within the Asian summer monsoon anticyclone associated with the convective transport of strong biospheric CO2 uptake signal over South Asia. During September as the anticyclone decays, a spreading of this low-CO2 area in the UT is observed in the vertical profiles of CO2 over the Pacific Rim of continental East Asia. Simulation results identify the influence of anthropogenic and biospheric CO2 fluxes in the seasonal evolution of the spatial CO2 distribution over the Asia-Pacific region. It is inferred that a substantial contribution to the UT CO2 over the northwestern Pacific comes from continental East Asian emissions in spring; but in the summer monsoon season, the prominent air mass origin switches to South Asia and/or Southeast Asia with a distinct imprint of the biospheric CO2 uptake. The CONTRAIL CO2 data provide useful constraints to model estimates of surface fluxes and to the evaluation of the satellite observations, in particular for the Asia-Pacific region.

An Approach to Estimate Atmospheric Greenhouse Gas Total Columns Mole Fraction from Partial Column Sampling

This study presents a new conceptual approach to estimate total column mole fractions of CO2 and CH4 using partial column data. It provides a link between airborne in situ and remote sensing observations of greenhouse gases. The method relies on in situ observations, external ancillary sources of information (e.g., atmospheric transport models), and a regression kriging framework. We evaluate our new approach using National Oceanic and Atmospheric Administration’s (NOAA’s) AirCore program—in situ vertical profiles of CO2 and CH4 collected from weather balloons. Our paper shows that under the specific conditions of this study and assumption of unbiasedness, airborne observations up to 6500–9500 m altitude are required to achieve comparable total column CO2 mole fraction uncertainty as the Total Carbon Column Observing Network (TCCON) network provides, given as a precision of the ratio between observed and true total column-integrated mole fraction, assuming 400 ppm XCO2 (2σ, e.g., 0.8 ppm). If properly calibrated, our approach could be applied to vertical profiles of CO2 collected from aircraft using a few flask samples, while retaining similar uncertainty level. Our total column CH4 estimates, by contrast, are less accurate than TCCON’s. Aircrafts are not as spatially constrained as TCCON ground stations, so our approach adds value to aircraft-based vertical profiles for evaluating remote sensing platforms.

Biosphere Atmosphere Exchange of CO2, H2O Vapour and Energy during Spring over a High Altitude Himalayan Forest in Eastern India

For the first time, the exchange of greenhouse gases, such as CO2 and H2O vapour, between the biosphere and the atmosphere at an eastern Himalayan site in India has been investigated. This study was carried out over a high altitude (2286 m asl) evergreen coniferous forest (27.04°N, 88.08°E), where we measured the fluxes of CO2 and H2O vapour along with the sensible and latent energy using the eddy covariance method both above (38 m) and within (8 m) the canopy, the soil-CO2 flux and the vertical profile of CO2 during spring (March–April) in 2015. The mean eddy flux of CO2 above the canopy was –2.8 ± 6.5 µmol m–2 s–1, whereas it was 0.6 ± 0.4 µmol m–2 s–1 within the canopy. The mean flux of H2O vapour above the canopy (1.5 ± 1.8 mmol m–2 s–1) was three times higher than within the canopy (0.5 ± 0.6 mmol m–2 s–1). The mean flux of CO2 emitted from the soil surface was 1.6 ± 0.1 µmol m–2 s–1. The diurnal variation showed high sequestration of CO2 during daytime, when the negative flux increased beyond –10 µmol m–2 s–1. We observed that precipitation significantly enhanced CO2 sequestration (by approximately fourfold) as well as H2O vapour emissions (by approximately threefold) by the tall canopies. Overall, during the entire study period, the net ecosystem exchange (NEE) was –656.5 g CO2 m–2, suggesting that the evergreen coniferous forest in the eastern Himalaya acts as a net sink of CO2 during spring. Therefore, we can estimate the sequestration of anthropogenic carbon emission by the eastern Himalayan forest ecosystem, improving the national greenhouse gas inventory.