Atmospheric CO2 Emissions Research Articles

Photoassisted CO2 Conversion to Fuels

AbstractIn the context of the on‐going change from fossil fuels to renewable energy sources, there is much interest in decreasing atmospheric CO2 emissions. One of the possibilities is to use CO2 as feedstock of fuels and chemicals. While some catalytic CO2 transformations are well known processes, they consume a considerable amount of energy to occur at significant rates and in the classical processes this energy is again produced by burning fossil fuels. For this reason, there is much current interest in developing light assisted CO2 transformations, including, but not limited to, artificial photosynthesis. Rather than a comprehensive review, the present article describes a range of approaches for CO2 activation based either on the direct CO2 excitation with deep UV light or on the use of solar photocatalysts. Due to the extension of the field, this article is focused on two photocatalyst types, namely, TiO2 containing plasmonic Au nanoparticles and graphene‐semiconductor heterojunctions. It will be emphasized the opportunities that bimetallic plasmonic nanoparticles offer to implement on commercial TiO2 visible light photoresponse and selectivity towards CO2 reduction. It will also be commented that adsorption of Cu2O onto defective graphene increases the photocatalytic activity of the copper semiconductor over one order of magnitude for CO2 photomethanation. The last section includes some comments about possible alternatives to go beyond the current efficiencies in light assisted CO2 conversion with the aim of triggering new research in the area.

Global Pyrogenic Carbon Production During Recent Decades Has Created the Potential for a Large, Long‐Term Sink of Atmospheric CO2

AbstractFires play an important role in the terrestrial biosphere carbon cycle, not only through direct carbon release but also contributing to a potential long‐term storage as pyrogenic carbon (PyC). PyC is formed through fires, and, because it may resist further biological and chemical degradation, is more stable in soil and sediment than original biomass. At the global scale, contributions of fires to both atmospheric CO2 emissions and PyC accumulation are potentially large but difficult to estimate. Our analysis was based on existing simulation results from two different modeling approaches (Global Fire Emissions Database version 4 [GFED4s] and Terrestrial Ecosystem Model version 6 [TEM6]) that used global area burned data to provide recent, retrospective estimates of CO2 emissions from vegetation combustion, together with published, biome‐ and continental‐scale conversion ratios that relate CO2 emissions to PyC production (PyC/CO2) during combustion. The estimates of global CO2 emissions from fires differed substantially between the two models' results. GFED4s estimated 2,041 Tg C/year during the 2000–2016 time period, whereas the TEM6 estimate was considerably lower at 643 Tg C/year from 2000 to 2010. Global PyC production estimates from fires were 153.4 ± 18.7 and 49.5 ± 4.9 Tg C/year based on the emission estimates from GFED4s and TEM6, respectively. Our results suggest that African tropical savanna fires produced the largest amount of CO2 emissions and PyC among global biomes, the most significant interannual variations in CO2 emissions and PyC production were found in tropical forests, and the magnitude of PyC produced by fires each year represented a potentially significant long‐term sink of atmospheric CO2.

Recommendations for calculation of the global warming potential of aviation including the radiative forcing index

There are specific effects of emissions in high altitude, which lead to a higher contribution of aviation to the problem of climate change than just the emission of CO2 from burning fuels. The exact relevance is subject to scientific debate, but there is a consensus that aircrafts have an impact that is higher than just their contribution due to the direct CO2 emissions. The gap between this scientific knowledge on the one side and the missing of applicable GWP (global warming potential) factors for relevant emissions on the other side are an important shortcoming for life cycle assessment (LCA) or carbon footprint (CF) studies which aim to cover all relevant environmental impacts of the transport services investigated. In this paper, the state of the art concerning the accounting for the specific effects of aircraft emissions in LCA and CF studies is discussed. Therefore, the relevant literature was evaluated, and practitioners were asked for the approaches used by them. Five major approaches are identified ranging from an RFI (radiative forcing index) factor of 1 (no factor at all) to a factor 2.7 for the total aircraft CO2 emissions. If only emissions in the higher atmosphere are considered, RFI factors between 1 and 8.5 are used or proposed in practice. For the time being, an RFI of 2 on total aircraft CO2 (or 5.2 for the CO2 emissions in the higher atmosphere if using present models in ecoinvent) is recommended to be used in LCA and CF studies because it is based on the latest scientific publications; this basic literature cannot be misinterpreted. Furthermore, it is also recommended by some political institutions. These factors can be multiplied by the direct CO2 emissions of the aircraft to estimate the total global warming potential.

Pressure transient technique to constrain CO2 plume boundaries

Carbon dioxide (CO2) has been injected in the subsurface permeable formations as a means to cut atmospheric CO2 emissions and/or enhance oil recovery (EOR). It is important to constrain the boundaries of the CO2 plume in the target formation and/or other formations hosting the CO2 migrated from the target formation. Monitoring methods and technologies to assess the CO2 plume boundaries over time within a reservoir of interest are required. Previously introduced methods and technologies on pressure monitoring to detect the extent of the CO2 plume require at least two wells, i.e. pulser and observation wells. We introduce pressure transient technique requiring single well only. Single well pressure transient testing (drawdown/buildup/injection/falloff) is widely used to determine reservoir properties and wellbore conditions. Pressure diagnostic plots are used to identify different flow regimes and determine the reservoir/well characteristics. We propose a method to determine the plume extent for a constant rate pressure transient test at a single well outside the CO2 plume. Due to the significant contrast between mobility and storativity of the CO2 and native fluids (oil or brine), the CO2 boundary causes deviation in the pressure diagnostic response from that corresponding to previously identified heterogeneities. Using the superposition principle, we develop a relationship between the deviation time and the plume boundary. We demonstrate the applicability of the proposed method using numerically generated synthetic data corresponding to homogeneous, heterogeneous, and anisotropic cases to evaluate its potential and limitations. We discuss ways to identify and overcome the potential limitations for application of the method in the field.

Beach-cast seagrass wrack contributes substantially to global greenhouse gas emissions

Seagrass ecosystems have received a great deal of attention recently for their ability to capture and store carbon, thereby helping to mitigate climate change. However, their carbon-sink capacity could be offset somewhat if exported plant material – which accounts for ∼90% of total leaf production – undergoes microbial breakdown and is emitted into the atmosphere as a greenhouse gas. Here we measured emissions (CO2 and CH4) from the breakdown of exported seagrass plant material, focusing on beach-cast ‘wrack’. We tested two seagrass species; Zostera nigricaulis and Amphibolis antarctica, which have contrasting morphologies and chemistries. We found that both species of wrack were substantial sources of CO2, but not CH4, during the decomposition process. Biomass loss and the coinciding CO2 emissions occurred over the 30-day experiment, and the pattern of CO2 emissions over this time followed a double exponential model (R2 > 0.92). The initial flux rate was relatively high, most likely due to rapid leaching of labile compounds, then decreased substantially within the 2–9 days, and stabilizing at < 3 μmol g−1 d−1 during the remaining decomposition period. Additionally, seagrass wrack cast high up on beaches that remained dry had 72% lower emissions than wrack that was subjected to repeated wetting in the intertidal zone. This implies that relocation of seagrass wrack by coastal resource managers (e.g. from water's edge to drier dune areas) could help to reduce atmospheric CO2 emissions. Scaling up, we estimate the annual CO2-C flux from seagrass wrack globally is between 1.31 and 19.04 Tg C yr−1, which is equivalent to annual emissions of 0.63–9.19 million Chinese citizens. With climate change and increasing coastal development expected to accelerate the rate of wrack accumulation on beaches, this study provides timely information for developing coastal carbon budgets.

Natural Ocean Alkalinity for Carbon Storage — Natural Engineering Method Practice

To achieve its latest requirements—the Paris climate goal (1.5°C), the UNFCCC needs to fulfill its basic commitments of promoting to make sustainable use of natural carbon sinks/reservoirs. In particular, it is imperative to make a breakthrough in the utilization of marine carbon sinks/reservoirs (accounting for more than 93% of the earth's natural carbon sinks/reservoirs) as soon as possible. Recent actual surveys and studies of several long-running large and medium-sized Eurasian power plants (a total of about 12 GW (Gigawatt), including a refinery and a marine tanker), have found that these commercial scale seawater scrubbing flue gas desulfurization (FGD) projects have captured substantially more CO2 than SO2 into the marine water column. These technical facts can explain that within the current national and international environmental regulations, there is a safe and marine eco-friendly use of natural ocean alkalinity for carbon storage to reduce the CO2 atmospheric emissions of fossil energy, which has been contributing to the atmosphere for well over 25 years. Based on the above technical facts and basic principles of marine chemistry, a natural engineering mitigation method is proposed. With this method, a portion of CO2 leaves the atmosphere and enters the ocean under controlled flux and rate to react with the natural alkalinity of the ocean (not artificial chemicals alkalinity) for ocean carbon storage. This method thus forms the technical foundation of a reversible, controllable (safe), and sustainable climate mitigation strategy, which can possibly mitigate climate change while avoiding ocean acidification (eliminating the root cause of ocean acidification: greenhouse chemical effects). Therefore, the natural seawater carbon capture and storage (NSW CCS) program was designed by using natural engineering mitigation methods, as the practical technology of using ocean natural alkalinity carbon sink/reservoir in a large scale, the main features of which are only using natural seawater with no additional artificial chemicals in the whole process. The entire cost of this CCS program is less than US$15/ton CO2; when the capture rate is 10%, the plant power consumption rate is about 1.4%; when the capture rate is 90%, plant power consumption rate is higher, about 10%, with a great potential for decline after the establishment of market structure. The funding threshold for pilot demonstration projects is low, and the program can be implemented step by step, which is conducive to the rapid deployment of commercial-scale projects, establishment of market structure and industrial chain, and development of new mitigation technologies and strategies. In view of the global mobility of oceans, it is recommended to carry out international cooperation under the management of UNFCCC Paris climate targets and initiate commercial demonstration research projects (including marine environmental monitoring and impact assessment system construction) with the progressive mode of capture rate, which use ocean natural alkalinity carbon storage. These projects can be prioritized to deploy in large point sources such as coastal power plants, refineries, and the international ocean shipping field.

On the Path to Commercial CCS: Scaling from Field Demonstration to Regional Hub

Commercial-scale industrial Carbon Capture Utilization and Storage (CCUS) has long been an objective to reduce carbon dioxide (CO2) emissions and increase storage and production potential. As a technology, it is deemed critical for achieving CO2 reductions that can lead to Paris Agreement targets for below 2°C global average temperature increases. Many models to mitigate atmospheric CO2 emissions call for CCUS from bioenergy, also known as BECCS, as a significant contributor to help achieve these climate goals. Facilitating the development of commercial-scale projects from industrial sources of CO2 has been a strategic process across multiple phases leading ultimately to a succession of projects of increasing scale in the Central United States. Four major CCS projects in the Illinois Basin region, USA exemplify the strategic pathway defined more than a decade ago by the U.S. Department of Energy – National Technology Laboratory (US DOE). Starting in 2003, the Midwest Geological Sequestration Consortium (MGSC), one of the US DOE Regional Carbon Sequestration Partnerships, has been working to define regional CCUS potential, conducting small enhanced oil and enhanced coalbed methane projects, and conducting a large-scale deep saline CCS storage project. As a direct outcome of the Illinois Basin – Decatur Project (IBDP), a one million tonne storage demonstration, the Illinois Industrial Sources CCS Project (ICCS) has expanded infrastructure and injection potential to industrial commercial-scale. Advancing CCS even further, the CarbonSAFE Macon County and Wabash feasibility projects seek to conduct physical and social site characterization leading to the development of storage complexes with the potential to receive and store over 50 million tonnes of CO2 from single or multiple sources. These projects combined provide an excellent example of how leveraging research, public-private partnerships, resources, relationships, and experience move CCUS forward regionally resulting in infrastructure to support storage and utilization hubs. This paper provides a brief summary of CCUS projects the Illinois Basin region of the US Midwest, and discusses of areas of overlap between projects, as well as the ways in which resources and collaborations have benefitted and challenged the individual projects. Broader lessons are provided to facilitate scale-up with CCS and CCUS deployment throughout the region.

A Highly Porous Copper Electrocatalyst for Carbon Dioxide Reduction.

Electrochemical reduction of carbon dioxide (CO2 ) is an appealing approach toward tackling climate change associated with atmospheric CO2 emissions. This approach uses CO2 as the carbon feedstock to produce value-added chemicals, resulting in a carbon-neutral (or even carbon-negative) process for chemical production. Many efforts have been devoted to the development of CO2 electrolysis devices that can be operated at industrially relevant rates; however, limited progress has been made, especially for valuable C2+ products. Herein, a nanoporous copper CO2 reduction catalyst is synthesized and integrated into a microfluidic CO2 flow cell electrolyzer. The CO2 electrolyzer exhibits a current density of 653 mA cm-2 with a C2+ product selectivity of ≈62% at an applied potential of -0.67 V (vs reversible hydrogen electrode). The highly porous electrode structure facilitates rapid gas transport across the electrode-electrolyte interface at high current densities. Further investigations on electrolyte effects reveal that the surface pH value is substantially different from the pH of bulk electrolyte, especially for nonbuffering near-neutral electrolytes when operating at high currents.

Influence of SO2 on CO2 Transport by Pipeline for Carbon Capture and Storage Technology: Evaluation of CO2/SO2 Cocapture

CO2 capture and storage (CCS) is an important technology for avoiding atmospheric CO2 emissions, which are principally originated from fossil fuels combustion. Anthropogenic CO2 contains impurities that can strongly modify the properties of the stream. Several authors have shown that some of these impurities, such as SO2 present in emissions from sulfur-containing fuels, could be favorable for some steps of the process, and the possibility of cocapture has been proposed. To assess this possibility with regard to the transport stage of CCS, we determined the influence of SO2 on selected parameters of transport by pipeline (minimal operational pressure, pressure and density drops, distance between boosters, booster power, and inner diameter of the pipeline, and the Joule-Thomson coefficient). For this purpose, we obtained new and accurate experimental data for the density and vapor–liquid equilibrium of five CO2 + SO2 mixtures under conditions of interest for CCS and speed of sound data for four of them. We...

Investigation of convective-conductive heat transfer in geothermal system

Abstract Geothermal energy is one of the well-known types of renewable energies that can be considered as a promising alternative to fossil fuels in order to mitigate the CO2 emission in atmosphere. Geothermal energy has recently been used for heating and cooling systems in many countries of the world. Therefore, studying such kind of energy seems important and necessary. This paper studies the heat transfer processes in a borehole heat exchanger (BHE). The flow of fluid in a BHE has been considered with different geometries and heat transfer processes are modeled numerically and in a finite volume method through convection and conductivity. First, a single U-shaped BHE was modeled and its thermal properties were investigated and then other geometries were studied to obtain the best geometry and heat transfer efficiency. In order to increase the heat transfer in the inner part of the pipes, the fin with the given specifications was used and the modeling was carried out and the thermal parameters were compared for three BHE’s with different geometries. In the final part, optimization results are presented, and the interaction of parameters on the Nusselt number and friction coefficient have been investigated. Also, the desirability of optimization and reliability is given to the results presented in percentage terms. Comparing the results of this article with the results of previous research shows a very good agreement and therefore the applied method is reliable and accurate.

Time-lapse VSP monitoring for CO2 injection: A case study in ordos, China

Carbon dioxide capture and storage (CCS) is considered one of the options for reducing atmospheric emissions of CO2 from human activities. Geological storage, as an important method to reduce CO2 emissions, may lead to a series of geomechanical problems due to the large amounts of gas injected. Starting in 2010, the Shenhua CCS demonstration project in the Ordos Basin, China, which is the first and the largest full-chain saline aquifer storage project in Asia, had injected a total of 0.3 million tons (Mt) of CO2 by 2015. The VSP method was used to monitor seismic properties. Baseline and repeat VSP surveys were conducted in May 2011 and August 2013, respectively. This paper focuses on the techniques of wave field separation and consistency processing. The upgoing P wave was used to image the time-lapse profiles by the VSP-CDP stack. Comparing the results, it was found that the time-lapse VSP method provides accurate and high-resolution images to monitor the CO2 diffusion range. The reliability of the method was then checked by the lithology of the target layer. With this current time-lapse VSP and geological analysis, the results showed that there is no obvious danger of gas leakage in the project, and that CO2 has been sealed in five predetermined reservoirs.

The economic impacts of ocean acidification on shellfish fisheries and aquaculture in the United Kingdom

Ocean acidification may pose a major threat to commercial fisheries, especially those for calcifying shellfish species. This study was undertaken to estimate the potential economic costs resulting from ocean acidification on UK wild capture and aquaculture shellfish production. Applying the net present value (NPV) and partial equilibrium (PE) models, we estimate both direct and economy-wide economic losses of shellfish production by 2100. Estimates using the NPV method show that the direct potential losses due to reduced shellfish production range from 14% to 28% of fishery NPV. This equates to annual economic losses of between ö3 and ö6 billion of the UK’s GDP in 2013, for medium and high emission scenarios. Results using the PE model showed the total loss to the UK economy from shellfish production and consumption ranging from ö23–ö88 million. The results from both the direct valuation and predicted estimate for the economic losses on shellfish harvest indicate that there are regional variations due to different patterns of shellfish wild-capture and aquaculture, and the exploitation of species with differing sensitivities to ocean acidification. These results suggest that the potential economic losses vary depending on the chosen valuation method. This analysis is also partial as it did not include a wider group of species in early-life-stages or predator-prey effects. Nevertheless, findings show that the economic losses to the UK and its devolved administrations due to ocean acidification could be substantial. We conclude that addressing ocean acidification with the aim of preserving commercially valuable shellfish resources will require regional, national or international solutions using a combined approach to reduce atmospheric CO2 emissions and shift in focus to exploit species that are less vulnerable to ocean acidification.

Mitigation of greenhouse gases emissions impact and their influence on terrestrial ecosystem.

Nowadays, one of the most important challenges faced by the humanity in the current century is the increasing temperature on Earth, caused by a growing emission of greenhouse gases into the atmosphere. Terrestrial ecosystems, as an important component of the carbon cycle, play an important role in the sequestration of carbon, which is a chance to improve the balance of greenhouse gases. Increasing CO2 absorption by terrestrial ecosystems is one way to reduce the atmospheric CO2 emissions. Sequestration of CO2 by terrestrial ecosystems is not yet fully utilized method of mitigating CO2 emission to the atmosphere. Terrestrial ecosystems, especially forests, are essential for the regulation of CO2 content in the atmosphere and more attention should be paid to seeking the natural processes of CO2 sequestration.

Atmospheric Emissions from Oil and Gas Extraction and Production in Greece

This paper addresses the atmospheric emissions of CO2, SO2, H2S, NOx, and volatile organic compounds (VOCs) from oil and gas extraction and production in the Gulf of Kavala. This is currently the only location of oil and gas production in Greece. Facilities are located both offshore (Kappa and Delta platforms) and onshore (Sigma plant), producing sweet gas, sour gas, and sour crude oil. This study presents the characteristics of atmospheric emissions, including emission measurements, emission inventories, and concentration measurements, from a central monitoring station and twelve total sulfation stations, the latter aiming to assess the effects of atmospheric emissions to air quality. During the development of the monitoring system, special attention was placed to sulfur compounds, since the existence of sour gas and sour crude oil was expected to lead to increased amounts of H2S and SO2. One of the main findings of the present study is that if the prevailing wind direction is considered (i.e., from N–NE), then the central monitoring station is not located downwind of the onshore and offshore facilities; therefore, its position should be re-examined. The emission inventories showed that flaring at the offshore facilities is the main source of SO2 emissions, while SO2 emissions and ambient concentrations were well below the relevant standards. Furthermore, CO2 emissions were lower by 67.73% as compared to 2008, when emissions reached a maximum. This was attributed to more energy demanding activities during that period, and mainly to the operation of turbines between 2007 and 2009. Since it is expected that the exploitation of hydrocarbons as well as oil and gas extraction and production will increase in the future in Greece, appropriate measures should be taken to ensure environmental protection, such as the use of up-to-date emission control technologies and a flare gas recovery system.

The Effect of Initial Chemical State of Copper Nanoparticles Towards C2 Products for Electrochemical CO2 Reduction

The electrocatalytic reduction of CO2 to value-added products with utilizing the renewable electricity is a promising alternative for using fossil fuels and an attractive solution for mitigating the constant rise in atmospheric CO2 emissions. Among all kinds of metal catalysts, copper is the only one that has capability to produce considerable amounts of hydrocarbons and alcohols at a moment. However, the selectivity control towards products is a main challenge for using a copper as a catalyst. In recent studies, oxide-derived copper has emerged as an efficient electrocatalyst candidate for better C-C coupling ability and lower overpotentials. Although the reason for this enhanced ability is still under debate, the residual oxygen or Cu+ in nanostructured subsurface region has been proposed as a critical factor to improve selectivity towards C2 products and in-situ analyses examined this suggestion. Here, we synthesized copper nanoparticles (NPs) directly grown on carbon support by wet-chemically facile one-pot method. We prepared two kinds of Cu NPs with different morphology and chemical state by controlling the synthesis temperature. The one is Cu2O with cube shape and the other is Cu/CuOx with sphere shape, which are confirmed by TEM, XPS and Cu K-edge XANES analysis. The electrocatalytic CO2 reduction reaction (CO2 RR) was conducted in 0.1 M KHCO3 aqueous solution and the effect of initial chemical state of copper on C2H4 selectivity was investigated. We observed that C2H4 selectivity is highly improved when the initial chemical state of copper nanoparticles is Cu2O compared to Cu/CuOx with the faradaic efficiency is 55 % and 20 %, respectively at -1.05 V (vs. RHE). For the verification of the reason for improved activity, we conducted XANES experiment and TEM analysis in the middle of CO2 RR. We conclude that the subsurface oxygen enhance catalytic activity and stability for ethylene production. Figure 1. TEM images of (A) cubic Cu2O/C and (B) sphere Cu/CuOx/C Figure 1

Catalysts for CO2 Electroreduction to Hydrocarbons and Oxygenates

Rising atmospheric carbon dioxide (CO2) levels and the associated rise in global temperatures have been brought to light as major global concerns. In fact, annual atmospheric CO2 emissions have risen from about 2 Gt to 10 Gt in the last 5 decades.1 Electricity production (via fossil fuel, etc.) is a large contributor, accounting for 37% of total CO2 emissions, and therefore scientists have turned to renewable energy as a mitigation strategy.2,3 Another widely-studied approach has been to reduce CO2 to value-added chemicals and fuels (carbon monoxide, ethanol, formic acid, etc.). Previous works have aimed at increasing the feasibility of the CO2 electroreduction (CO2RR). Being able to improve and control the selectivity of CO2RR would greatly contribute to its industrial application. Developing thermodynamically efficient and kinetically active catalysts is a key part of CO2RR. Depending on the catalyst or operating conditions, a variety of products can be formed.4 Hydrocarbons and oxygenates, such as ethanol and methanol, are attractive products because of their high-energy density and variability in application.5 For example, methanol is a feedstock for the industrially mature methanol to gasoline (MTG) process, which has a 95% thermal energy conversion efficiency.6 Although some state of the art electrocatalysts for CO2 electroreduction can produce CO and HCOOH at high selectivity (>80%) and energy efficiency (>60%), the selective production of higher hydrocarbons, especially oxygenates such as ethanol and methanol, is still lacking.7 In this talk, we will present examples of various catalysts for the selective electroreduction of CO2 to oxygenates and hydrocarbons using an alkaline flow electrolyzer at ambient conditions. These catalysts include copper supported on metal oxides (Cu/MxOy), copper-based alloys, etc. Electroanalysis results of the Cu/MxOy catalysts include selective production of C1 products (CO and methane) with traces of methanol when compared to copper nanoparticles. The copper-based alloys depict Faradaic efficiencies of up to 75% for C2 products (ethylene and ethanol). Acknowledgement We gratefully acknowledge financial support from I2CNER and the SURGE Fellowship for UN. References Hansen J., Kharecha, P., et al., PLoS One, 2013.Oerlemans, J., Science, 2005, 308(5722), 675-677.https://www.eia.gov Accessed 05/29/2017.R.M. Jhong, S. Ma, P.J.A. Kenis, Curr. Opin. Chem. Eng., 2013, 2, 191-199.Ma, M. Sadakiyo, R. Luo, M. Heima, M. Yamauchi, P.J.A. Kenis, J. Power Sources, 2016, 301, 219-228.L. Spath, D.C. Dayton, NREL/TP-510-34929, 2003.J. Martin, G.O. Larrazabál, J. Pérez-Ramírez. Green Chem., 2015.

Diurnal, synoptic and seasonal variability of atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in the Paris megacity area

Abstract. Most of the global fossil fuel CO2 emissions arise from urbanized and industrialized areas. Bottom-up inventories quantify them but with large uncertainties. In 2010–2011, the first atmospheric in situ CO2 measurement network for Paris, the capital of France, began operating with the aim of monitoring the regional atmospheric impact of the emissions coming from this megacity. Five stations sampled air along a northeast–southwest axis that corresponds to the direction of the dominant winds. Two stations are classified as rural (Traînou – TRN; Montgé-en-Goële – MON), two are peri-urban (Gonesse – GON; Gif-sur-Yvette – GIF) and one is urban (EIF, located on top of the Eiffel Tower). In this study, we analyze the diurnal, synoptic and seasonal variability of the in situ CO2 measurements over nearly 1 year (8 August 2010–13 July 2011). We compare these datasets with remote CO2 measurements made at Mace Head (MHD) on the Atlantic coast of Ireland and support our analysis with atmospheric boundary layer height (ABLH) observations made in the center of Paris and with both modeled and observed meteorological fields. The average hourly CO2 diurnal cycles observed at the regional stations are mostly driven by the CO2 biospheric cycle, the ABLH cycle and the proximity to urban CO2 emissions. Differences of several µmol mol−1 (ppm) can be observed from one regional site to the other. The more the site is surrounded by urban sources (mostly residential and commercial heating, and traffic), the more the CO2 concentration is elevated, as is the associated variability which reflects the variability of the urban sources. Furthermore, two sites with inlets high above ground level (EIF and TRN) show a phase shift of the CO2 diurnal cycle of a few hours compared to lower sites due to a strong coupling with the boundary layer diurnal cycle. As a consequence, the existence of a CO2 vertical gradient above Paris can be inferred, whose amplitude depends on the time of the day and on the season, ranging from a few tenths of ppm during daytime to several ppm during nighttime. The CO2 seasonal cycle inferred from monthly means at our regional sites is driven by the biospheric and anthropogenic CO2 flux seasonal cycles, the ABLH seasonal cycle and also synoptic variations. Enhancements of several ppm are observed at peri-urban stations compared to rural ones, mostly from the influence of urban emissions that are in the footprint of the peri-urban station. The seasonal cycle observed at the urban station (EIF) is specific and very sensitive to the ABLH cycle. At both the diurnal and the seasonal scales, noticeable differences of several ppm are observed between the measurements made at regional rural stations and the remote measurements made at MHD, that are shown not to define background concentrations appropriately for quantifying the regional (∼ 100 km) atmospheric impact of urban CO2 emissions. For wind speeds less than 3 m s−1, the accumulation of local CO2 emissions in the urban atmosphere forms a dome of several tens of ppm at the peri-urban stations, mostly under the influence of relatively local emissions including those from the Charles de Gaulle (CDG) Airport facility and from aircraft in flight. When wind speed increases, ventilation transforms the CO2 dome into a plume. Higher CO2 background concentrations of several ppm are advected from the remote Benelux–Ruhr and London regions, impacting concentrations at the five stations of the network even at wind speeds higher than 9 m s−1. For wind speeds ranging between 3 and 8 m s−1, the impact of Paris emissions can be detected in the peri-urban stations when they are downwind of the city, while the rural stations often seem disconnected from the city emission plume. As a conclusion, our study highlights a high sensitivity of the stations to wind speed and direction, to their distance from the city, but also to the ABLH cycle depending on their elevation. We learn some lessons regarding the design of an urban CO2 network: (1) careful attention should be paid to properly setting regional (∼ 100 km) background sites that will be representative of the different wind sectors; (2) the downwind stations should be positioned as symmetrically as possible in relation to the city center, at the peri-urban/rural border; (3) the stations should be installed at ventilated sites (away from strong local sources) and the air inlet set up above the building or biospheric canopy layer, whichever is the highest; and (4) high-resolution wind information should be available with the CO2 measurements.

What is the best endpoint for assessing environmental risk associated with acidification caused by CO2 enrichment using mussels?

Carbon capture and storage is a technology that has been widely determined to be one of the best choices for the short-term reduction of atmospheric CO2 emissions. The aim of this study was to analyze the effects of CO2 enrichment in the ocean on the mussel species Mytilus galloprovincialis using three different endpoints: mortality, embryo-larval development, and neutral red retention time assays (NRRT). Acute effects were found to be associated with a pH values of 6.0 while citotoxity effects and embryo-larval development were associated with a pH value of 7.0. The NRRT assay and embryo-larval development can be recommended as good endpoints for assessing the environmental risk associated with acidification by CO2 enrichment because they provide sensitive responses on the effects of changes in seawater pH on mussels in a short period of time. Moreover, this study may support policymakers in finding appropriate solutions for the conservation of marine ecosystems.

Acidified seawater increases accumulation of cobalt but not cesium in manila clam Ruditapes philippinarum

The pH of seawater around the world is expected to continue its decline in the near future in response to ocean acidification that is driven by heightened atmospheric CO2 emissions. Concomitantly, economically-important molluscs that live in coastal waters including estuaries and embayments, may be exposed to a wide assortment of contaminants, including trace metals and radionuclides. Seawater acidification may alter both the chemical speciation of select elements as well as the physiology of organisms, and may thus pose at risk to many shellfish species, including the manila clam Ruditapes philippinarum. The bioconcentration efficiency of two common radionuclides associated with the nuclear fuel cycle, 134Cs and 57Co, were investigated by exposing live clams to dissolved 134Cs and 57Co at control (pH = 8.1) and two lowered pH (pH = 7.8 and 7.5) levels using controlled aquaria. The uptake and depuration kinetics of the two radionuclides in the whole-body clam were followed for 21 and 35 days, respectively. At steady-state equilibrium, the concentration factor (CFss) for 57Co increased as the pH decreased (i.e. 130 ± 5, 194 ± 6, and 258 ± 10 at pH levels 8.1, 7.8 and 7.5, respectively), whereas the 134Cs uptake was not influenced by a change in pH conditions. During depuration, the lowest depuration rate constant of 57Co by the manila clam was observed at the intermediate pH of 7.8. An increase in the accumulation of 57Co at the intermediate pH value was thought to be caused mainly by the aragonitic shell of the clam, as well as the low salinity and alkalinity of seawater used in the experiment. Considering that accumulation consists of uptake and depuration, among the three pH conditions moderately acidified seawater enhanced most the accumulation of 57Co. Accumulation of 134Cs was not strongly influenced by a reduced pH condition, as represented by an analogous uptake constant rate and CFss in each treatment. Such results suggest that future seawater pH values that are projected to be lower in the next decades, may pose a risk for calcium-bearing organisms such as shellfish.

Turkey's energy system development: linking an energy supply model with an industrial simulation model and solving it iteratively

Turkey is in the progress to include nuclear energy to its electricity generation capacity. The energy modelling studies for Turkey mainly focus on usage of renewable energy and local fossil fuels and include nuclear power plants (NPP) only with their electricity generation capacities without taking into consideration the front- and back-ends of the nuclear fuel cycle. This study takes into consideration the life cycle assessment (LCA) of nuclear energy based on optimisation of energy system costs and usage of energy resources under atmospheric CO2 and SO2 emission constraints using MESSAGE iteratively with an industrial simulation model. This iterative modelling calculates the marginal costs of final energy generation and energy demands for domestic production. The results of this study are assessed using economic, environmental and social indicators. The study concludes that both environmental and nuclear energy scenarios are viable options to set national atmospheric CO2 and SO2 emission targets for Turkey.