Large Point Sources Research Articles

The attempt to estimate annual variability of NOx emission in Poland using Sentinel-5P/TROPOMI data

Information on the annual variability of nitrogen oxides (NOx) emissions is needed in air quality modeling. Emission inventories like EMEP or E-PRTR provide only the total amounts of NOx emission per year. Satellite data on atmospheric composition allows for the quantification of air pollutants emissions and the monitoring of their changes in time. In this study the Sentinel-5P/TROPOMI NO2 tropospheric vertical column (TVC) data from the area of Poland and its border areas from the period of May 2018–November 2021 were used to estimate the NOx lifetime, as well as total NOx emission from Poland area, and NOx emissions from 28 large point sources (LPSs), with their annual variability. The box model (BM) was used to estimate NOx emissions. A novelty is the use of NO2 TVC data in a circular area around each LPS with a radius depending on the wind speed. Furthermore, a new search streak method (SSM) for LPS emission estimation was proposed, and the results were compared with these obtained by the BM method assuming the 5th percentile of NO2 TVC as the emission background (BM5). The estimated monthly and hourly NOx emissions were compared with the stack measurement data for 4 power plants and with the E-PRTR data for all analyzed LPSs. The annual variability of NOx lifetime estimates, higher in winter and lower in summer, is roughly consistent with earlier estimates based on SCIAMACHY and OMI data for mid-latitude sites. The results showed difficulties in estimating NOx emissions for the winter months, whereas for the other seasons the inaccuracies and errors of estimation were much lower. When estimating NOx emission from the LPS using TROPOMI data, the BM5 method gives better results when the LPS is the dominant emission source, while the SSM method works better in an area with many significant emission sources. Comparison of the annual average NOx emission estimates obtained by the BM5 and SSM methods for 28 LPSs with the E-PRTR data showed that the average normalized BIAS is strongly correlated with the emission background around the LPS. The introduction of an additional TROPOMI data selection criterion related to the wind direction sector significantly improves the quality of the results.

Direct Evidence of Coal Swelling and Shrinkage with Injecting CO2 and N2 Using in-situ Synchrotron X-ray Microtomography

Deep coal seams are one of the world’s most widespread deposits for carbon dioxide (CO 2 ) disposal and are generally located near large point sources of CO 2 emissions. The injection of CO 2 into coal seams has great potential to sequester CO 2 while simultaneously enhancing coalbed methane (CO 2 -ECBM) recovery. Pilot tests of CO 2 -ECBM have been conducted in coal seams worldwide with favorable early results. However, one of the main technical barriers in coal seams needs to be resolved: Injecting CO 2 reduces coal permeability and well injectivity. Here, using in situ synchrotron X-ray microtomography, we provide the first observational evidence that injecting nitrogen (N 2 ) can reverse much of this lost permeability by reopening fractures that have closed due to coal swelling induced by CO 2 adsorption. Our findings support the notion that injecting minimally treated flue gas—a mixture of mainly N 2 and CO 2 —is an attractive alternative for ECBM recovery instead of pure CO 2 injection in deep coal seams. Firstly, flue gas produced by power plants could be directly injected after particulate removal, thus avoiding high CO 2 -separation costs. Secondly, the presence of N 2 makes it possible to maintain a sufficiently high level of coal permeability. These results suggest that flue-gas ECBM for deep coal seams may provide a promising path toward net-zero emissions from coal mines.

Retrieving CH4-emission rates from coal mine ventilation shafts using UAV-based AirCore observations and the genetic algorithm–interior point penalty function (GA-IPPF) model

Abstract. There are plenty of monitoring methods to quantify gas emission rates based on gas concentration measurements around the strong sources. However, there is a lack of quantitative models to evaluate methane emission rates from coal mines with less prior information. In this study, we develop a genetic algorithm–interior point penalty function (GA-IPPF) model to calculate the emission rates of large point sources of CH4 based on concentration samples. This model can provide optimized dispersion parameters and self-calibration, thus lowering the requirements for auxiliary data accuracy. During the Carbon Dioxide and Methane Mission (CoMet) pre-campaign, we retrieve CH4-emission rates from a ventilation shaft in Pniówek coal mine (Silesia coal mining region, Poland) based on the data collected by an unmanned aerial vehicle (UAV)-based AirCore system and a GA-IPPF model. The concerned CH4-emission rates are variable even on a single day, ranging from 621.3 ± 19.8 to 1452.4 ± 60.5 kg h−1 on 18 August 2017 and from 348.4 ± 12.1 to 1478.4 ± 50.3 kg h−1 on 21 August 2017. Results show that CH4 concentration data reconstructed by the retrieved parameters are highly consistent with the measured ones. Meanwhile, we demonstrate the application of GA-IPPF in three gas control release experiments, and the accuracies of retrieved gas emission rates are better than 95.0 %. This study indicates that the GA-IPPF model can quantify the CH4-emission rates from strong point sources with high accuracy.

(Invited) Hydrogen Assisted Carbonate Electrolysis for Direct Air Capture of CO2

Reduction of greenhouse gases is vital for the long-term environmental health of the planet. While there has been progress in reducing CO2 emissions at large point sources, a significant portion of the CO2 emitted each year in the United States is released from distributed sources, like cars, smaller factories, and farms. Direct capture of CO2 from ambient air is therefore necessary for the ultimate reduction of greenhouse gas emissions in the atmosphere. However, capturing the CO2 in ambient air presents a much greater challenge due to the dilute nature of the CO2, requiring different strategies than carbon capture from concentrated CO2 waste streams.We are developing a novel process for the capture and containment of CO2 from air into a purified, concentrated CO2 stream that can be redirected for use as a feedstock for a wide variety of applications, including chemical manufacturing and syngas formation. This process involves the capture of CO2 in a concentrated KOH solution using a high-surface area air contactor to form potassium carbonate. The potassium carbonate is then efficiently electrolyzed in a hydrogen-assisted process to regenerate the CO2 at a low operating potential, increasing the electrical efficiency of the process while producing concentrated and purified CO2. In addition, water, hydrogen, and KOH are also regenerated as byproducts that can be recycled back into the CO2 capture and electrolysis processes, reducing both overall energy and chemical consumption.Using a custom designed test stand and traditional electrolysis cell design, we have demonstrated voltage of <1.8 V at 100 mA/cm2 for potassium carbonate conversion to carbon dioxide at the anode, with concomitant H2 and KOH production at the cathode, based on potassium-selective ion exchange across the membrane. Furthermore, using a custom 3-compartment electrolysis flow cell and ion-selective membranes, we successfully demonstrated hydrogen-assisted carbonate electrolysis, with hydrogen consumption at the anode, hydrogen and KOH production at the cathode, and CO2 formation from potassium carbonate in an internal flow-through compartment, at 1.4 V at 50 mA/cm2. Further improvements in operating conditions and cell components and design should decrease the operating voltage significantly, to <1 V at 100 mA/cm2. Acknowledgement: The project is financially supported by the Department of Energy’s ARPA-E Office under the Grant DE-AR0001495

CO2 capture from wet flue gas using transition metal inserted porphyrin-based metal-organic frameworks as efficient adsorbents

CO2 capture from large point sources is indispensable for achieving 1.5 degree target as long as fossil fuels are still in use. Selective adsorption of CO2 from flue gas constitutes a promising CO2 capture technology, thanks to the development of numerous fascinating solid adsorbents in the past three decades. However, very few adsorbents can retain their required performance in the presence of moisture which is unfortunately always the case in reality. In this study, we elevated the CO2 adsorption and separation performance of a water-stable aluminum-based porphyrin metal-organic frameworks (Al-PMOF) by inserting transition metals as adsorption sites. Compared with the pristine Al-PMOF and other four transition metals (TMs) incorporated PMOFs (Al-PMOF(M)), the Co-inserted Al-PMOF (Al-PMOF(Co)) exhibited the highest CO2 adsorption capacity (3.32 mmol/g) and highest CO2/N2 and CO2/CH4 selectivity (87 and 20, respectively) at 273 K and 1.0 bar. After three consecutive cyclic moisture treatments, the CO2 adsorption capacity of Al-PMOF(Co) remained almost unchanged. More importantly, the dynamic binary CO2/N2 breakthrough adsorption of Al-PMOF(Co) exhibited negligible differences in CO2 adsorption capacities between dry and wet flue gas conditions, suggesting that TMs incorporated Al-PMOF possess excellent moisture-resistant properties. Mechanistic studies using the combined in situ synchrotron infrared spectroscopic and powder X-ray diffraction together with density functional theory calculations unambiguously revealed the inserted metals are the dominant CO2 adsorption sites. This study materializes the rational design of efficient adsorbents for CO2 capture and contributes to mitigating climate change.

Process Intensification of CO2 Desorption

Anthropogenic climate change due to, among other causes, unhindered CO2 emissions is a major concern worldwide. The post-combustion capture (PCC) process using a solvent, known as chemical absorption, is currently the most effective way to reduce CO2 emissions from large point sources. However, high capital investment costs when using the conventional packed bed absorber/desorber technology and high energy requirements during solvent regeneration are the primary obstacles for its large-scale implementation. Different process intensification (PI) technologies to desorb CO2 from the solvent have been introduced to mitigate the energy consumption compared to the conventional packed bed technology. This work reviews different technologies for intensification of CO2 desorption. In this context, rotating packed beds, microreactors, and membrane contactors have been explored as potential alternatives to intensify the desorption because of their superior mass and heat transfer. Alternative energy sources like ultrasound and microwaves have also been used to improve the desorption performance of conventional equipments. PI can also be realized by using novel solvents with improved desorption kinetics in combination with intensification equipment. Thus in this review, a comprehensive assessment of different existing PI technologies based on regeneration energies and regeneration efficiencies relative to conventional technology is presented. The intensification of mass transfer for the different technologies is compared, and a new parameter, named the regeneration factor, is proposed to evaluate the performance of PI equipment. This study outlines the advances in process intensification of CO2 desorption technologies to date and presents an overview of the merits and limits of all technologies.

Evaluation of correlated Pandora column NO2 and in situ surface NO2 measurements during GMAP campaign

Abstract. To validate the Geostationary Environment Monitoring Spectrometer (GEMS), the GEMS Map of Air Pollution (GMAP) campaign was conducted during 2020–2021 by integrating Pandora Asia Network, aircraft, and in situ measurements. In the present study, GMAP-2020 measurements were applied to evaluate urban air quality and explore the synergy of Pandora column (PC) NO2 measurements and surface in situ (SI) NO2 measurements for Seosan, South Korea, where large point source (LPS) emissions are densely clustered. Due to the difficulty of interpreting the effects of LPS emissions on air quality downwind of Seosan using SI monitoring networks alone, we explored the combined analysis of both PC-NO2 and SI-NO2 measurements. Agglomerative hierarchical clustering using vertical meteorological variables combined with PC-NO2 and SI-NO2 yielded three distinct conditions: synoptic wind-dominant (SD), mixed (MD), and local wind-dominant (LD). These results suggest meteorology-dependent correlations between PC-NO2 and SI-NO2. Overall, yearly daytime mean (11:00–17:00 KST) PC-NO2 and SI-NO2 statistical data showed good linear correlations (R=∼0.73); however, the differences in correlations were largely attributed to meteorological conditions. SD conditions characterized by higher wind speeds and advected marine boundary layer heights suppressed fluctuations in both PC-NO2 and SI-NO2, driving a uniform vertical NO2 structure with higher correlations, whereas under LD conditions, LPS plumes were decoupled from the surface or were transported from nearby cities, weakening correlations through anomalous vertical NO2 gradients. The discrepancies suggest that using either PC-NO2 or SI-NO2 observations alone involves a higher possibility of uncertainty under LD conditions or prevailing transport processes. However, under MD conditions, both pollution ventilation due to high surface wind speeds and daytime photochemical NO2 loss contributed to stronger correlations through a decline in both PC-NO2 and SI-NO2 towards noon. Thus, Pandora Asia Network observations collected over 13 Asian countries since 2021 can be utilized for detailed investigation of the vertical complexity of air quality, and the conclusions can be also applied when performing GEMS observation interpretation in combination with SI measurements.

Quantifying methane emissions from the global scale down to point sources using satellite observations of atmospheric methane

Abstract. We review the capability of current and scheduled satellite observations of atmospheric methane in the shortwave infrared (SWIR) to quantify methane emissions from the global scale down to point sources. We cover retrieval methods, precision and accuracy requirements, inverse and mass balance methods for inferring emissions, source detection thresholds, and observing system completeness. We classify satellite instruments as area flux mappers and point source imagers, with complementary attributes. Area flux mappers are high-precision (&lt;1 %) instruments with 0.1–10 km pixel size designed to quantify total methane emissions on regional to global scales. Point source imagers are fine-pixel (&lt;60 m) instruments designed to quantify individual point sources by imaging of the plumes. Current area flux mappers include GOSAT (2009–present), which provides a high-quality record for interpretation of long-term methane trends, and TROPOMI (2018–present), which provides global continuous daily mapping to quantify emissions on regional scales. These instruments already provide a powerful resource to quantify national methane emissions in support of the Paris Agreement. Current point source imagers include the GHGSat constellation and several hyperspectral and multispectral land imaging sensors (PRISMA, Sentinel-2, Landsat-8/9, WorldView-3), with detection thresholds in the 100–10 000 kg h−1 range that enable monitoring of large point sources. Future area flux mappers, including MethaneSAT, GOSAT-GW, Sentinel-5, GeoCarb, and CO2M, will increase the capability to quantify emissions at high resolution, and the MERLIN lidar will improve observation of the Arctic. The averaging times required by area flux mappers to quantify regional emissions depend on pixel size, retrieval precision, observation density, fraction of successful retrievals, and return times in a way that varies with the spatial resolution desired. A similar interplay applies to point source imagers between detection threshold, spatial coverage, and return time, defining an observing system completeness. Expanding constellations of point source imagers including GHGSat and Carbon Mapper over the coming years will greatly improve observing system completeness for point sources through dense spatial coverage and frequent return times.

Improving NOx emission estimates in Beijing using network observations and a perturbed emissions ensemble

Abstract. Emissions inventories are crucial inputs to air quality simulations and represent a major source of uncertainty. Various methods have been adopted to optimise emissions inventories, yet in most cases the methods were only applied to total anthropogenic emissions. We have developed a new approach that updates a priori emission estimates by source sector, which are particularly relevant for policy interventions. At its core is a perturbed emissions ensemble (PEE), constructed by perturbing parameters in an a priori emissions inventory within their respective uncertainty ranges. This PEE is then input to an air quality model to generate an ensemble of forward simulations. By comparing the simulation outputs with observations from a dense network, the initial uncertainty ranges are constrained, and a posteriori emission estimates are derived. Using this approach, we were able to derive the transport sector NOx emissions for a study area centred around Beijing in 2016 based on a priori emission estimates for 2013. The absolute emissions were found to be 1.5–9 × 104 Mg, corresponding to a 57 %–93 % reduction from the 2013 levels, yet the night-time fraction of the emissions was 67 %–178 % higher. These results provide robust and independent evidence of the trends of traffic emission in the study area between 2013 and 2016 reported by previous studies. We also highlighted the impacts of the chemical mechanisms in the underlying model on the emission estimates derived, which is often neglected in emission optimisation studies. This work paves forward the route for rapid analysis and update of emissions inventories using air quality models and routine in situ observations, underscoring the utility of dense observational networks. It also highlights some gaps in the current distribution of monitoring sites in Beijing which result in an underrepresentation of large point sources of NOx.

Influence of the Grid Resolutions on the Computer-Simulated Surface Air Pollution Concentrations in Bulgaria

The present study aims to demonstrate the effects of horizontal grid resolution on the simulated pollution concentration fields over Bulgaria. The computer simulations are performed with a set of models used worldwide—the Weather Research and Forecasting Model (WRF)—the meteorological preprocessor, the Community Multiscale Air Quality Modeling System (CMAQ)—chemical transport model, Sparse Matrix Operator Kernel Emissions (SMOKE)—emission model. The large-scale (background) meteorological data used in the study were taken from the ‘NCEP Global Analysis Data’ with a horizontal resolution of 1° × 1°. Using the ‘nesting’ capabilities of the WRF and CMAQ models, a resolution of 9 km was achieved for the territory of Bulgaria by sequentially solving the task in several consecutive nested areas. Three cases are considered in this paper: Case 1: The computer simulations result from the domain with a horizontal resolution (both of the emission source description and the grid) of 27 km.; Case 2: The computer simulations result from the domain with a horizontal resolution (both of the emission source description and the grid) of 9 km.; Case 3: A hybrid case with the computer simulations performed with a grid resolution of 9 km, but with emissions such as in the 27 km × 27 km domain. The simulations were performed, for all the three cases, for the period 2007–2014 year, thus creating an ensemble large and comprehensive enough to reflect the most typical atmospheric conditions with their typical recurrence. The numerical experiments showed the significant impact of the grid resolution not only in the pollution concentration pattern but also in the demonstrated generalized characteristics. Averaged over a large territory (Bulgaria); however, the performances for cases one and two are quite similar. Bulgaria is a country with a complex topography and with several considerably large point sources. Thus, some of the conclusions made, though based on Bulgarian-specific experiments, may be of general interest.

Optimizing utilization of point source and atmospheric carbon dioxide as a feedstock in electrochemical CO2 reduction

SummaryThe electrochemical reduction of carbon dioxide is a potential pathway for production of fuels and chemicals that uses atmospheric carbon dioxide as a feedstock. Here, we present an analysis of the potential for carbon dioxide from point sources and via direct air capture to be utilized in electrochemical reduction under different market scenarios. We show that developing a network for production of these products at scale requires capture and utilization of significant portions of the carbon dioxide that is currently emitted from large stationary point sources. Because carbon dioxide point sources are spatially and compositionally variable, their use for carbon dioxide reduction depends on electricity prices, capture cost, and location. If the power sector in the United States is decarbonized, carbon dioxide supply decreases significantly, increasing the importance of utilizing other carbon dioxide streams, and increasing the likelihood that direct air capture plays a role in supplying carbon dioxide feedstocks.

Elucidating the important thermo physical characterization properties of amine activated hybrid novel solvents for designing post-combustion CO2 capture unit

The surge in energy demand globally has resulted in high level of CO2 emissions through large industrial point sources. Chemical or physical absorption is one of the widely used methods utilized for large scale CO2 capture. The utility of any solvent in CO2 absorption system requires the detail fundamental understanding of physicochemical properties associated with the solvent. In the present work, physicochemical properties of six different aqueous blends of hybrid solvents of (3-aminopropyl) triethoxysilane (TESA), N-methyldiethanolamine (MDEA), sulfolane (TMSO2), 1-butyl-3-methyl-imidazolium acetate ([bmim][Ac]) activated by 1-(2-aminoethyl) piperazine (AEP), bis-(3-aminopropyl)amine (APA) and 2-methyl piperazine (2-MPZ) are studied. Various important physiochemical properties needed for process design viz. density, viscosity, surface tension, refractive index and sound velocity are measured over a broad range of temperature (298.15–333.15) K and concentration. Redlich-Kister and Grunberg-Nissan models have been used for correlating density and viscosity. Statistical regression have been applied for correlating sound velocity, refractive index and surface tension. Important derived properties of the proposed solvents have been also evaluated through empirical correlations.

Environmental impacts of the production of synthetic natural gas from industrial carbon dioxide

Power-to-Gas technologies (PtG) are regarded as promising options to defossilize the energy system by converting and storing renewable electricity to gases. When combined with carbon capture and utilization from large point sources, such as energy intensive and hard-to-abate sectors, where a major part of CO 2 emissions cannot be avoided, PtG technologies can also play a role to mitigate CO 2 emissions. However, these technologies have several environmental impacts throughout their lifetimes that must be assessed, due to the use of resources, materials, and energy, as well as the formation of chemical by-products. Using a Life Cycle Assessment (LCA) methodology, this paper aims to assess the most significant environmental impacts of an integrated PtG system including the conversion of renewable energy to hydrogen through water wind-based electrolysis, that is further converted to synthetic natural gas (SNG) by reacting with captured CO 2 from a cement plant flue gas. More precisely, the present work innovates on both the technical and methodological perspectives. An advanced CO 2 capture process is implemented, using mixed amines solvent and innovative configuration to reduce the energy consumption to 2.3 GJ per tCO 2 captured, and include an optimized heat integration with the CO 2 conversion step. A hybrid approach combining physical and economic input data is also considered for the life cycle inventory. Additionally, both subdivision and system expansion via substitution approaches are applied to consider the multi-functionality of the systems. Simulation results show that the PtG process with CO 2 captured from cement plants flue gas reduces the overall GHG emissions by 76%. Similarly, the fossil resource scarcity is drastically reduced by over 80% thanks to the heat integration between the CO 2 capture and the CO 2 conversion processes, but also thanks to the substitution of natural gas by the CO 2 -based SNG. Nevertheless, environmental impacts of PtG are higher than conventional natural gas production for other impact categories, including freshwater eutrophication, terrestrial acidification, and mineral resource scarcity. Both data uncertainties, assessing the knowledge base underlying the input data parameters, and sensitivity analysis, assessing the value range of the parameters respectively to the environmental indicators, are conducted to test the results and highlight the uncertainty hotspots.

A Pathway Towards Net-Zero Emissions in Oil Refineries

Rapid industrialization and urbanization have increased the demand for both energy and mobility services across the globe, with accompanying increases in greenhouse gas emissions. This short paper analyzes strategic measures for the abatement of CO2 emissions from oil refinery operations. A case study involving a large conversion refinery shows that the use of post-combustion carbon capture and storage (CCS) may only be practical for large combined emission point sources, leaving about 30% of site-wide emissions unaddressed. A combination of post-combustion CCS with a CO2 capture rate well above 90% and other mitigation measures such as fuel substitution and emission offsets is needed to transition towards carbon-neutral refinery operations. All of these technologies must be configured to minimize environmental burden shifting and scope 2 emissions, whilst doing so cost-effectively to improve energy access and affordability. In the long run, scope 3 emissions from the combustion of refinery products and flaring must also be addressed. The use of synthetic fuels and alternative feedstocks such as liquefied plastic waste, instead of crude oil, could present a growth opportunity in a circular carbon economy.

Assessment of oil and gas fields in California as potential CO2 storage sites

California's total annual greenhouse gas (GHG) emissions (425.3 MtCO2e) in 2018 were about 6.4% of the US total (6,677 MtCO2e) and around 1% of global emissions. About 39% of 2018 GHG emissions in California were from the industrial and electrical sectors. Many of these emissions were from large stationary point sources and were suitable for carbon capture retrofit with subsequent storage of the captured carbon dioxide (CO2) in geological formations. Previous studies of California found suitable geology and CO2 storage resource. This study refines and furthers prior work using a three-stage screening process of oil fields, gas fields, and underground natural gas storage (UGS) sites by combining criteria from previous studies while excluding sites that pose technical risk or are located in regions with surface restrictions including sensitive habitats and dense populations. In the first stage, 129 CO2 storage sites in California were identified using qualification criteria based upon formation properties including geological conditions and pore pressure. The second stage identified sensitive sites by applying conservative screens including seismic activity, faulting, population density, restricted lands, and sensitive habitats. During the third stage, 61 CO2 potential storage sites were identified by subtraction of stage 2 areas from stage 1. The potential storage volume in the third stage ranged from 1.0 to 2.0 GtCO2. Finally, we applied a scoring system with seven parameters to rank the 61 potential sites based on subsurface technical criteria. The scored sites are classified as high priority, medium priority, and sites for future study. Prospective CO2 storage sites with high and moderate priority were selected and linked to CO2 sources. There are 14 prospective sites (above 20 MtCO2 storage resource per site) with a total storage resource of 1024 MtCO2 distributed in Northern and Southern California. Of these sites, there are 9 potential CO2-EOR sites and 1 depleted oil field with a total estimated CO2 storage volume of ∼800 MtCO2 in the Southern San Joaquin and Ventura Basin. These 10 prospective sites with a storage resource greater than 20 MtCO2 could potentially deliver more than 20 years of storage with an average injection rate of 40 MtCO2/year. The remaining 4 highly prospective sites are in Northern California. Study results also suggest that saline formations should be re-evaluated in concert with storage in oil, gas, and natural gas storage reservoirs.

Tall tower eddy covariance measurements of CO2 fluxes in Vienna, Austria

This study reports on three years (2018–2020) of turbulent CO2 fluxes measured at 144 m above the city of Vienna, Austria using an eddy covariance system installed on the A1 Arsenal radio tower. Overall CO2 flux data availability after quality control filtering (49%) was comparable to that observed by other studies of urban and suburban eddy covariance measurements. Average monthly CO2 fluxes followed seasonal trends in temperature-based proxies of heating demand, with the highest fluxes observed in the winter months. When analysing separate trends for the two dominating wind directions, this seasonality was most pronounced for the flows from the north-west when flux footprints overlapped with Vienna's most populated and urbanised districts and fluxes. For flows from the south-east, when flux footprints covered areas of built-up and industrial land yet were dominated by green urban spaces and arable land, the seasonality was much less marked and average monthly CO2 fluxes were generally lower, particularly in winter. Weekday-weekend patterns as well as weekday diurnal variations in CO2 generally followed respective trends in local traffic counts; however, flux correlations with hourly traffic counts on weekends and public holidays were much weaker. Weekend/public holiday diurnal trends in CO2 fluxes indicated an influence of vegetation fluxes on net CO2 flux variations between midday and late afternoon in spring and summer. Furthermore, variations in weekend/public holiday CO2 fluxes from night-time to morning periods suggested a partial night-time decoupling between turbulent exchange at 144 m and the net fluxes at the surface. While the influence of CO2 advection could not be quantified, the pronounced morning flux peaks indicated that CO2 released to the atmosphere during these partially decoupled, night-time periods accumulated to some extent and was subsequently mixed vertically with the morning increase in boundary layer depth. Indeed, the calculated annual fluxes suggested that positive and negative 30-min biases were largely offset when averaging over longer time intervals. The 2018 flux of 10.89 kt CO2 km−2 was in close agreement with the annual CO2 emissions estimate of 10.19 kt CO2 km−2 derived from an official emissions inventory (excluding large point source emissions). A similar annual flux was observed in 2019; however, the substantially lower flux in 2020 likely reflected emissions reductions associated with the COVID-19 pandemic. Comparison of normalised daytime CO2 fluxes between years indicated that the initial lockdown led to a ca. 50–60% reduction in net CO2 emissions from Vienna's most populated and urbanised districts. This study thus provides further evidence that defensible estimates of urban CO2 fluxes can be achieved with tall tower eddy covariance.

From CO2 sources to sinks: Regulatory challenges for trans-boundary trade, shipment and storage

Carbon Capture and Storage (CCS) technologies have been hailed as a solution to climate change with capacity not only to reduce atmospheric carbon di-oxide (CO2) but also to achieve net-zero emission by the mid-21st century. CO2 captured (either directly from the atmosphere or from large point sources), is compressed and transported to storage sites, either via pipelines or through shipping. Often, the CCS projects are deployed nationally where capture, transport and storage take place within the jurisdiction of one State. However, wide scale deployment of CCS projects is imperative for global matching of CO2 sources to sinks. To that end, the outreach of CCS technology needs to go beyond the developed world. Studies have indicated that developing countries have vast storage resource potential. Internationalization of CCS projects where CO2 is captured in one State and is then transported to another State for storage raises a number of challenges particularly in terms of trans-boundary transport and storage. This paper explores some of these challenges particularly in terms of international trade law, liability framework for shipping and storage and potential of insurance to act as a stop-gap arrangement until a regulatory regime is in place. It examines questions such as: whether CO2 and CCS technologies are environmental goods and services under trade law; are there any regulatory frameworks in place to ensure liability against long-term health and safety as well environmental risks, and; what role can insurance industry play in promoting global deployment of CCS projects?

A review of technologies for carbon capture, sequestration, and utilization: Cost, capacity, and technology readiness

AbstractThe continued rise in anthropogenic carbon dioxide (CO2) emissions and increase in atmospheric CO2 concentration has led to calls from experts, including the Intergovernmental Panel on Climate Change that has estimated that global warming needs to be limited to 1.5 °C above preindustrial levels to avoid the worst effects of climate change, and that carbon neutrality would need to be achieved globally by 2050 to meet this target. Achieving carbon neutrality by mid‐century will rely on successful implementation and widespread adoption of technologies for reducing emissions from large point sources of CO2, direct CO2 capture from the air, as well as storage and utilization technologies that would convert CO2 to a form that would ensure safety and permanency of storage. In this paper, engineering solutions for CO2 capture, utilization, and storage are reviewed with a focus on technology readiness level, and cost. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Reconstructing and quantifying methane emissions from the full duration of a 38-day natural gas well blowout using space-based observations

We quantify and characterize methane emissions from a natural gas well blowout in Louisiana, USA in 2019 using TROPOMI (TROPOspheric Monitoring Instrument) methane observations and VIIRS (Visible Infrared Imaging Radiometer Suite) gas flare detections. We use TROPOMI data in a Bayesian inversion to optimize daily methane emissions while VIIRS-based radiant heat data are used to estimate the amount of gas flared. This hybrid approach allows for the characterization of methane emissions during both the flaring and venting phases of the blowout, where more than half of the blowout duration was associated with flaring. We estimate overall emissions of this 38-day event at 49 (21–63) Gg, which is lower than reported by the gas company but exceeds all known US point sources emitting at the time in terms of emission rate. We estimate that over 80% of total emissions come from the venting phase, leaving the flaring phase responsible for only a small fraction of total emissions. We show that routine satellite operations from global-scale observing instruments such as TROPOMI and VIIRS when combined can provide a detailed assessment of quantitative greenhouse gas emissions from large point sources including stochastic events and thus these data could be used for regulatory enforcement.

Process Intensification through the Electrochemical Upgrading of Biomass-Derived Species for Sustainable Chemicals and Fuels

Biomass refineries are distributed in nature, co-located near the source of the biomass. This is very different than the traditional petroleum refineries which operate as large point sources for chemical manufacturing. The difference in scale and available utilities between a biomass and a petroleum refinery means the chemical processes that go on in the biomass refineries need to be re-evaluated. There is a significant opportunity to use electrochemical methods to upgrade biomass-derived species at the biorefinery. Electrochemical processes are more amenable to the smaller scales of the biorefinery and require fewer inputs than traditional chemical processes. For example, electrochemical hydrogenation and hydrogenolysis of biomass-derived species does not require hydrogen gas or steam as utilities, rather protons are sourced from the aqueous electrolyte to participate in the reduction and energy is provided through electricity. Additionally, through the use of renewable electricity, the upgrading process can be further decarbonized. The reaction parameters must be understood and well-controlled to enable the implementation of electrochemical hydrogenation and hydrogenolysis with high activities and selectivities. The electrolyte, temperature, electrocatalyst, and duration that the products are exposed to the electrolyte all influence the reaction outcome. For example, in the electrochemical hydrogenation and hydrogenolysis of furfural, a pH of less than 3.4 on a copper catalyst should be used if 2-methyl furan is targeted as a product. Additionally, the 2-methyl furan should be removed from the reactor in situ to prevent side reactions from occurring. Additional reaction engineering and separation strategies for electrochemical upgrading of biomass will also be discussed.