Carbon Mass Balance Research Articles

A mass balance approach to investigating geochemical controls on secondary water quality impacts at a crude oil spill site near Bemidji, MN

Secondary water quality impacts can result from a broad range of coupled reactions triggered by primary groundwater contaminants. Data from a crude-oil spill research site near Bemidji, MN provide an ideal test case for investigating the complex interactions controlling secondary impacts, including depleted dissolved oxygen and elevated organic carbon, inorganic carbon, CH4, Mn, Fe, and other dissolved ions. To better understand these secondary impacts, this study began with an extensive data compilation of various data types, comprising aqueous, sediment, gas, and oil phases, covering a 260m cross-sectional domain over 30years. Mass balance calculations are used to quantify pathways that control secondary components, by using the data to constrain the sources and sinks for the important redox processes. The results show that oil constituents other than BTEX (benzene, toluene, ethylbenzene, o-, m- and p-xylenes), including n-alkanes and other aromatic compounds, play significant roles in plume evolution and secondary water quality impacts. The analysis underscores previous results on the importance of non-aqueous phases. Over 99.9% of the Fe2+ plume is attenuated by immobilization on sediments as Fe(II) and 85–95% of the carbon biodegradation products are outgassed. Gaps identified in carbon and Fe mass balances and in pH buffering mechanisms are used to formulate a new conceptual model. This new model includes direct out-gassing of CH4 and CO2 from organic carbon biodegradation, dissolution of directly produced CO2, and sorption with H+ exchange to improve pH buffering. The identification of these mechanisms extends understanding of natural attenuation of potential secondary impacts at enhanced reductive dechlorination sites, particularly for reduced Fe plumes, produced CH4, and pH perturbations.

Black Carbon Measurements of Flame-Generated Soot as Determined by Optical, Thermal-Optical, Direct Absorption, and Laser Incandescence Methods

Black carbon (BC) is a primary particle matter component emitted as a result of incomplete combustion. Due to its light-absorbing nature, BC can exert both direct and indirect influence on global climate. There is no universal research or regulatory definition of BC; instead, a variety of instruments and analytical methods define BC operationally. This study used a constant, source-generated BC concentration in order to quantify the variation in BC measurements using 10 different instruments and methodologies. Instruments examined include a multiangle absorption photometer, a transmissometer, rack-mount, portable, and micro-aethalometers, a thermal-optical carbon analyzer (using IMPROVE, NIOSH 5040, and NIST-EPA methods), a single-particle soot photometer (SP2), and a three-wavelength photoacoustic soot spectrometer (PASS3). BC-bearing soot was generated using an ethylene-air diffusion flame, diluted to ∼100 μg/m3, which was subjected to simultaneous analyses. Measured BC and elemental carbon (EC) concentrations ranged from 20.5 to 39.9 μg/m3. BC concentrations measured by aethalometers and transmissometer instruments varied by <15%. However, measurements of BC were as much as 52% greater than EC determined by thermal-optical techniques. Gravimetric data from the current study suggest that the thermal-optical measurements of EC likely underestimated the carbon in flame soot samples, indicating an inability to close a carbon mass balance.

Reaction Process of Perfluorooctanesulfonic Acid (PFOS) Decomposed by DC Plasma Generated in Argon Gas Bubbles

Perfluorooctanesulfonic acid (PFOS: C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> H) is a bioaccumulative and environmentally persistent substance. PFOS cannot be decomposed by conventional water treatments; therefore, a new degradation method is required. PFOS can be efficiently degraded by dc plasma generated in gas bubbles. Since this process has yet to be elucidated, we investigated the by-products and the reaction process during the degradation of PFOS. Aqueous PFOS (initial concentration of 55.5 mg/L) was decomposed by dc plasma generated in argon gas bubbles for 600 min, and the concentrations of PFOS, perfluorocarboxylic acids (PFCAs: C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2n+1</sub> COOH, n=1-7), carbon dioxides, carbon monoxides, and fluoride ions were measured, but we did not achieve mass balances for carbon or fluorine. To detect the unknown by-products, both aqueous PFOS that was treated for 180 min and the gas released from the reactor were analyzed. C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> HF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2m</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> H (m=2-8) and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> HF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2i</sub> COOH (i=2-7) were detected in the liquid phase, and CHF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> HF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> , and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> were found in the gas phase. Given these by-products, it has been proposed that some PFOS is immediately thermally decomposed to carbon dioxides, fluoride ions, and hence forth., and the remaining PFOS is gradually degraded by the collisions of high energy particles, leading to the final products that include fluorocarbon gases and fluoride ions.

Understanding ultrafiltration membrane fouling by extracellular organic matter of Microcystis aeruginosa using fluorescence excitation–emission matrix coupled with parallel factor analysis

This study presents a novel approach evaluating the foulant properties of extracellular organic matter (EOM) on ultrafiltration (UF) by examining the organic matter properties of the feed, permeate, reversible and irreversible foulant layers using excitation–emission matrix coupled with parallel factor analysis (EEM–PARAFAC) together with dissolved organic carbon (DOC) and polysaccharide analysis. Fate of each EOM component as well as total carbon mass balance under various solution chemistries were illustrated, and major foulants and fouling mechanisms involved were identified. Component 1 (i.e. tryptophan-like substances) and polysaccharides were identified as the major foulants under all solution chemistries, but major irreversible foulants changed under different solution chemistries. Under the ambient solution chemistry, polysaccharides contributed more to irreversible fouling, while Component 1 fouling turned out to be more irreversible with the presence of calcium. Calcium bridging effect, pore blocking and initial pore-competition resulted in the changes above. The significant increase of irreversible fouling observed under acid condition was attributed to the extremely enhanced hydrophobic adhesion between hydrophobic foulants (Component 1 and Component 3) and polyethersulfone (PES) membrane. The proposed EEM–PARAFAC based approach proved suitable for major foulant identification and mechanism implication, suggesting its potential for analyzing membrane fouling caused by complex matrix.

Carbon mass balance and microbial ecology in a laboratory scale reactor achieving simultaneous sludge reduction and nutrient removal

Solids reduction in activated sludge processes (ASP) at source using process manipulation has been researched widely over the last two-decades. However, the absence of nutrient removal component, lack of understanding on the organic carbon, and limited information on key microbial community in solids minimizing ASP preclude the widespread acceptance of sludge minimizing processes. In this manuscript, we report simultaneous solids reduction through anaerobiosis along with nitrogen and phosphorus removals. The manuscript also reports carbon mass balance using stable isotope of carbon, microbial ecology of nitrifiers and polyphosphate accumulating organisms (PAOs). Two laboratory scale reactors were operated in anaerobic-aerobic-anoxic (A2O) mode. One reactor was run in the standard mode (hereafter called the control-SBR) simulating conventional A2O type of activated sludge process and the second reactor was run in the sludge minimizing mode (called the modified-SBR). Unlike other research efforts where the sludge minimizing reactor was maintained at nearly infinite solids retention time (SRT). To sustain the efficient nutrient removal, the modified-SBR in this research was operated at a very small solids yield rather than at infinite SRT. Both reactors showed consistent NH3–N, phosphorus and COD removals over a period of 263 days. Both reactors also showed active denitrification during the anoxic phase even if there was no organic carbon source available during this phase, suggesting the presence of denitrifying PAOs (DNPAOs). The observed solids yield in the modified-SBR was 60% less than the observed solids yield in the control-SBR. Specific oxygen uptake rate (SOUR) for the modified-SBR was almost 44% more than the control-SBR under identical feeding conditions, but was nearly the same for both reactors under fasting conditions. The modified-SBR showed greater diversity of ammonia oxidizing bacteria and PAOs compared to the control-SBR. The diversity of PAOs in the modified-SBR was even more interesting in which case novel clades of Candidatus Accumulibacter phosphatis (CAP), an uncultured but widely found PAOs, were found.

Improvement of Environmental Monitoring Technology on the basis of Carbon Mass Balance during CO2-enhanced Oil Recovery and Storage

Abstract This study reviewed the emission inventory of carbon injection, production, storage, and emission. Results indicated that only approximately 95% of injected CO2 can be measured. Approximately 92% to 95% of carbon was stored, 0.01% was leaked from soil, and the residual 5% may have come from leak paths or may have leaked from near-surface sources, such as underground water, through biological metabolism. To develop a carbon mass balance model for CO2 enhanced oil recovery projects, the emission part from soil and underground water, as well as the fixation by vegetation, should be carefully measured. The residual 5% that remains unmeasured should be proven, i.e., whether such amount is derived along leak paths or is emitted from near-surface sources. Findings could highlight the fate of carbon, provide some suggestions to guide the selection of environmental monitoring technology, and aid in establishing a common methodology to identify leak risks for carbon storage projects.

Anaerobic digestion of marine biomass for practical operation

Marine biomass such as seaweed and fishery waste is a potential energy source although it has not yet been practically utilized. This work focuses on renewable energy technologies, particularly anaerobic digestion, for the utilization of various organic wastes as energy resources. Primarily fundamental data for the efficient operation of an anaerobic digestion plant with marine biomass was obtained and a practical operation method was proposed using a simple model based on the carbon mass balance. Batch-processing experiments for seaweed, fishery waste and vegetable waste were carried out and each digestion characteristic was presented. The results indicate that fishery waste is the most efficient even though the accumulation of ammonium ions may inhibit methane production. Seaweeds are not efficient in either the production rate or the yield of methane gas. We investigated the efficient continuous operation for 6 biomass input scenarios with the proposed model. The results show that seaweed can be a useful supplement for the efficient operation.

Analysis of unburned carbon in industrial ashes from biomass combustion by thermogravimetric method using Boudouard reaction

A novel thermogravimetric method for the determination of unburned carbon in industrial ashes from biomass combustion using the strongly endothermic Boudouard reaction is proposed. The method does not require acid treatment to remove carbonates; it may also be used for samples containing a higher amount of portlandite, calcite and other mineral components typical for biomass-combustion ashes and is utilizable in the wide range of the content of unburned carbon. The correctness of the proposed determination was verified by carbon mass balance in 10 samples of industrial ashes. The interpretation of the course of the TG curves obtained was corroborated by differential scanning calorimetry.

Dynamic carbon budget of a large shallow lake assessed by a mass balance approach

To study the role of large and shallow hemiboreal lakes in carbon processing, we calculated a 3-year carbon mass balance for Lake Vortsjarv (Estonia) based on in situ measurements. This balance took into account hydrological and biogeochemical processes affecting dissolved inorganic (DIC), dissolved organic (DOC) and particulate organic (POC) carbon species. Accumulation varied greatly on a seasonal and yearly basis. The lake exported carbon during most of the year except during spring floods and in late autumn. In-lake processes were responsible for exporting POC and storing DOC while DIC switched between storage and export. The carbon cycle was alternatively dominated in 2009 by biogeochemical processes and in 2011 by riverine fluxes, whereas in 2010 the two process types were of the same magnitude. These results suggest that the role of large shallow lakes like Vortsjarv in the global C cycle is equally driven by hydrological factors, in particular seasonal water level changes, and by biogeochemical in-lake reactions.

Influence of Oxygen on Alcoholic Fermentation by a Wine Strain ofTorulaspora delbrueckii: Kinetics and Carbon Mass Balance

Torulaspora delbrueckii metabolism was assessed in a synthetic culture medium similar to grape must under various conditions: no aeration and three different oxygen feeds, in order to determine the effect of oxygen on metabolism. Carbon and nitrogen mass balances were calculated to quantify metabolic fluxes. The effect of oxygen was to decrease the flux of carbon going into the fermentation pathway in favor of growth. In the absence of aeration, higher amounts of glycerol were produced, probably to maintain the redox balance. The oxygen requirement of this strain was high, since even for the highest air supply oxygen became limiting after 24 h. Nevertheless, this strain developed well in the absence of oxygen and consumed 220 g/L of sugars (glucose/fructose) in 166 h at 20 °C, giving a good ethanol yield (0.50 g/g).

A large column analog experiment of stable isotope variations during reactive transport: II. Carbon mass balance, microbial community structure and predation

Here we report a combined analysis of carbon mass balance based on isotopic labeling and microbiological characterization during organic carbon stimulated bioreduction of a subsurface sediment in a large laboratory column experimental system. This combination of approaches allows quantification of both the cycling of carbon through multiple redox pathways and the associated spatial and temporal evolution of bacterial communities in response to this nutrient source. Carbon isotope mass balance facilitated by the use of 13C-labeled acetate as the electron donor showed evidence for a net loss of sediment organic carbon over the course of the amendment experiment. Furthermore, these data clearly demonstrated a source of isotopically labeled inorganic carbon that was not attributable to primary metabolism by acetate-oxidizing microorganisms. Fluid samples collected weekly over the duration of the 43-day amendment at <20cm intervals along the flow path were analyzed for microbial composition by pyrosequencing of ribosomal RNA genes. The microbial community composition was transient, with distinct occurrences of Azoarcus, Geobacter and multiple sulfate reducing species over the course of the experiment. In combination with DNA sequencing data, the anomalous carbon cycling process is shown to occur exclusively during the period of predominant Geobacter species growth. Pyrosequencing indicated, and targeted cloning and sequencing confirmed the presence of several bacteriovorous protozoa, including species of the Breviata, Planococcus and Euplotes genera. Cloning and qPCR analysis demonstrated that Euplotes species were most abundant and displayed a growth trajectory that closely followed that of the Geobacter population. These results suggest a previously undocumented secondary turnover of biomass carbon related to protozoan grazing that was not sufficiently prevalent to be observed in bulk concentrations of carbon species in the system, but was clearly identified in the partitioning of carbon isotopes. This study demonstrates evidence for predator-prey relationships that impact subsurface microbial community dynamics and provides a novel indication of the impact of this relationship on the flux of carbon through a system via the microbial biomass pool. Overall, our approach provides high temporal and spatial sampling resolution at field relevant flow rates, while minimizing effects of mixing and transverse dispersion. The result is a quantitative carbon budget accounting for a diversity of processes that should be considered for inclusion in reactive transport models that aim to predict carbon turnover, nutrient flux, and redox reactions in natural and stimulated subsurface systems.

An incubation study on the stability and biological effects of pyrogenic and hydrothermal biochar in two soils

SummaryThe success and feasibility of CO2‐sequestration through incorporation of biochar into soils depends strongly on the long‐term biochar stability and on the improvements of physical and microbial soil properties. In this study, the stability of two maize‐derived biochars (from pyrolysis and hydrothermal carbonization) and of a compost‐biochar mixture and their effects on microbial biomass and enzyme activity were determined in two soils during a 57‐day incubation. Soil samples amended with biochar increased soil organic carbon (SOC) content by 20 or 40%. Samples amended with hydrothermal biochar showed the largest respiration rates and the largest increase in microbial and enzymatic activity compared with the untreated controls. Carbon and 13C mass balances showed that between 13 and 16% of the added hydrochar was mineralized within 8 weeks. In the arable soil, hydrochar additions greatly stimulated the degradation of SOC, thus inducing positive priming effects. The mineralization of pyrogenic biochar (pyrochar and a pyrochar‐compost mixture) was significantly less (1.4–3%) and comparable to the SOC mineralization in the control soils.

Carbon sequestration in LCA, a proposal for a new approach based on the global carbon cycle; cases on wood and on bamboo

There are many recent proposals in life cycle assessment (LCA) to calculate temporary storage of carbon in bio-based products. However, there is still no consensus on how to deal with the issue. The main questions are: how do these proposals relate to each other, to what extent are they in line with the classical LCA method (as defined in ISO 14044) and the global mass balances as proposed by the IPCC, and is there really a need to introduce a discounting system for delayed CO2 emissions? This paper starts with an analysis of the widely applied specification of PAS 2050 and the ILCD Handbook, both specifying the credit for carbon sequestration as ‘optional’ in LCA. From this analysis, it is concluded that these optional calculations give rather different results compared to the baseline LCA method. Since these optional calculations are not fully in line with the global carbon mass balances, a new calculation method is proposed. To validate the new method, two cases (one on wood and one bamboo products) are given. These cases show the practical application and the consequences of the new approach. Finally, the main issue is evaluated and discussed: is it a realistic approach to allocate less damage to the same emission, when it is released later in time? This paper proposes a new approach based on the global carbon cycle and land-use change, translated to the level of individual products in LCA. It is argued that only a global growth of forest area and a global growth of application of wood in the building industry contribute to extra carbon sequestration, which might be allocated as a credit to the total market of wood products in LCA. This approach is different from approaches where temporary storage of carbon in trees is directly allocated to a product itself. In the proposed approach, there seems to be no need for a discounting system of delayed CO2 emissions. The advantage of wood and wood-based products can be described in terms of land-use change on a global scale in combination with a credit for heat recovery at the end-of-life (if applicable).

Plasma-catalysis of low TCE concentration in air using LaMnO3+δ as catalyst

The oxidative decomposition of trichloroethylene (TCE; 500–600ppmv) was investigated in synthetic (dry air) and humid air (RH=18%) with NTP (non thermal plasma) at atmospheric pressure, both in the absence and presence of lanthanum manganite catalyst at 150°C. In the absence of catalyst, TCE removal is enhanced with humidity (RH=18%) while O3 production is decreased. However, whatever the carrier gas the carbon mass balances are poor amounting to 25–30% due to the presence of polychlorinated by-products such as phosgene, dichloroacetyl chloride (DCAC) and trichloroacetaldehyde (TCAD). In the presence of catalyst, the TCE conversion significantly increased as compared to that of the plasma alone system. The perovskite catalyst can dissociate the in plasma produced ozone to oxygen radicals that decompose TCE. In dry air, the carbon mass balance keep rather poor (35% – 460J/L) due to the structural transformation of the catalyst with chlorine. In dry air, an optimum temperature of the catalytic reactor is found to be 100°C resulting from a compromise between catalyst deactivation and enhancement of the catalytic reactions. However, water remarkably promotes the carbon mass balance (75% – 460J/L) due to the beneficial role of water which acts as a chlorine scavenger at the surface of the catalyst, therefore retarding the perovskite degradation.

Impact of co-digestion on existing salt and nutrient mass balances for a full-scale dairy energy project

Anaerobic digestion of manure and other agricultural waste streams with subsequent energy production can result in more sustainable dairy operations; however, importation of digester feedstocks onto dairy farms alters previously established carbon, nutrient, and salinity mass balances. Salt and nutrient mass balance must be maintained to avoid groundwater contamination and salination. To better understand salt and nutrient contributions of imported methane-producing substrates, a mass balance for a full-scale dairy biomass energy project was developed for solids, carbon, nitrogen, sulfur, phosphorus, chloride, and potassium. Digester feedstocks, consisting of thickened manure flush-water slurry, screened manure solids, sudan grass silage, and feed-waste, were tracked separately in the mass balance. The error in mass balance closure for most elements was less than 5%. Manure contributed 69.2% of influent dry matter while contributing 77.7% of nitrogen, 90.9% of sulfur, and 73.4% of phosphorus. Sudan grass silage contributed high quantities of chloride and potassium, 33.3% and 43.4%, respectively, relative to the dry matter contribution of 22.3%. Five potential off-site co-digestates (egg waste, grape pomace, milk waste, pasta waste, whey wastewater) were evaluated for anaerobic digestion based on salt and nutrient content in addition to bio-methane potential. Egg waste and wine grape pomace appeared the most promising co-digestates due to their high methane potentials relative to bulk volume. Increasing power production from the current rate of 369 kW to the design value of 710 kW would require co-digestion with either 26800 L d−1 egg waste or 60900 kg d−1 grape pomace. However, importation of egg waste would more than double nitrogen loading, resulting in an increase of 172% above the baseline while co-digestion with grape pomace would increase potassium by 279%. Careful selection of imported co-digestates and management of digester effluent is required to manage salt and nutrient mass loadings and reduce groundwater impacts.

Carbon-14 age and chemical evolution of Ca(HCO3)2-type groundwater of age less than 8,000 years in a confined sandy and muddy Pleistocene aquifer, Japan

The Pleistocene Kimitsu aquifer was selected for examination of the relationship between groundwater age and chemical evolution of Ca(HCO3)2-type groundwater. For the most part, the aquifer is confined and composed mainly of quartz and feldspar with a small amount of calcite. The groundwater ages calculated by 14C were adjusted by using a carbon mass-balance method and corrected for effects of 14C diffusion. Groundwater ages in the Kimitsu aquifer vary from modern (upgradient) to approximately 2,400 years at 4.4 km from the edge of the recharge area. The 14C age was verified by groundwater velocity calculated from the hydraulic gradient and hydraulic conductivity. The confined groundwater evolved to Ca(HCO3)2-type around 50 years after recharge and this has been maintained for more than 8,300 years due to low chemical reactivity, derived from equilibrium with calcite, kaolinite and Ca-montmorillonite. In addition, high pH prevents the dissolution of Fe and Mn. Consequently, the rate of increase in electrical conductivity ranges from 10 to 30 μS/cm per 1,000 years. On the other hand, leakage from the deep region, which is recognized from high Cl– levels, causes remarkable increases in CH4 and HCO3 – concentrations, resulting in an apparent sulfidic zone at 500-m depth in most downgradient regions.

A data assimilation framework for constraining upscaled cropland carbon flux seasonality and biometry with MODIS

Abstract. Agroecosystem models are strongly dependent on information on land management patterns for regional applications. Land management practices play a major role in determining global yield variability, and add an anthropogenic signal to the observed seasonality of atmospheric CO2 concentrations. However, there is still little knowledge on spatial and temporal variability of important farmland activities such as crop sowing dates, and thus these remain rather crudely approximated within carbon cycle studies. In this study, we present a framework allowing for spatio-temporally resolved simulation of cropland carbon fluxes under observational constraints on land management and canopy greenness. We apply data assimilation methodology in order to explicitly account for information on sowing dates and model leaf area index. MODIS 250 m vegetation index data were assimilated both in batch-calibration for sowing date estimation and sequentially for improved model state estimation, using the ensemble Kalman filter (EnKF), into a crop carbon mass balance model (SPAc). In doing so, we are able to quantify the multiannual (2000–2006) regional carbon flux and biometry seasonality of maize–soybean crop rotations surrounding the Bondville Ameriflux eddy covariance site, averaged over 104 pixel locations within the wider area. (1) Validation at the Bondville site shows that growing season C cycling is simulated accurately with MODIS-derived sowing dates, and we expect that this framework allows for accurate simulations of C cycling at locations for which ground-truth data are not available. Thus, this framework enables modellers to simulate current (i.e. last 10 yr) carbon cycling of major agricultural regions. Averaged over the 104 field patches analysed, relative spatial variability for biometry and net ecosystem exchange ranges from ∼7% to ∼18%. The annual sign of net biome productivity is not significantly different from carbon neutrality. (2) Moreover, observing carbon cycling at one single field with its individual sowing pattern is not sufficient to constrain large-scale agroecosystem carbon flux seasonality. Study area average growing season length is 20 days longer than observed at Bondville, primarily because of an earlier estimated start of season. (3) For carbon budgeting, additional information on cropland soil management and belowground carbon cycling has to be considered, as such constraints are not provided by MODIS.

Gas phase photocatalytic oxidation of decane at ppb levels: Removal kinetics, reaction intermediates and carbon mass balance

Abstract This study focuses on the photocatalytic oxidation of decane at ppb levels, close to indoor air conditions. Although these concentrations are typical of indoor air volatile organic compound (VOC) levels, such conditions have been poorly investigated to date. Decane conversion rates higher than 90% were reached within 15 h for the highest initial concentration tested in the operating conditions used. Despite this high decane conversion, 18 reaction intermediates were detected in the gas phase. The main compounds, in terms of concentration level in the gas phase, were formaldehyde, acetaldehyde and propanal. The amounts of these compounds in the gas phase were linearly dependent on the initial decane concentration. A reaction pathway is proposed, based on reaction intermediate temporal profiles and the literature. It consists of six main steps describing the oxidation process from decane to CO and CO2. The influence of the relative humidity level on the diversity and amounts of reaction intermediates was also studied. It was shown that moisture tends to shift the equilibrium of intermediates adsorption toward desorption, resulting in a relative increase in intermediate quantities in the gas phase. However, the monitoring of CO and CO2 formation highlighted that, at the end of the reaction, a high mineralization rate could be obtained. Finally, an overview of the photocatalytic reaction is given through the carbon mass balance determined for various reaction advancements. This approach gives an overall evaluation of the photocatalytic process performance, from primary compound removal to reaction intermediate and mineralization.

Solvent Effect on Pathways and Mechanisms for d-Fructose Conversion to 5-Hydroxymethyl-2-furaldehyde: In Situ 13C NMR Study

Noncatalytic reactions of D-fructose were kinetically investigated in dimethylsulfoxide (DMSO), water, and methanol as a function of time at temperatures of 30-150 °C by applying in situ (13)C NMR spectroscopy. The products were quantitatively analyzed with distinction of isomeric species by taking advantage of site-selective (13)C labeling technique. In DMSO, D-fructose was converted first into 3,4-dihydroxy-2-dihydroxymethyl-5-hydroxymethyltetrahydrofuran having no double bond in the ring, subsequently into 4-hydroxy-5-hydroxymethyl-4,5-dihydrofuran-2-carbaldehyde having one double bond through dehydration, and finally into 5-hydroxymethyl-2-furaldehyde (5-HMF) having two double bonds. No other reaction pathways were involved, as shown from the carbon mass balance. In water, 5-HMF, the final product in DMSO, was generated with the precursors undetected and furthermore transformed predominantly into formic and levulinic acids and slightly into 1,2,4-benzenetriol accompanied by polymerization. D-glucose was also produced through the reversible transformation of the reactant D-fructose. In methanol, some kinds of anhydro-D-fructoses were generated instead of 5-HMF. The reaction pathways can thus be controlled by taking advantage of the solvent effect. The D-fructose conversion reactions are of the first order with respect to the concentration of D-fructose and proceed on the order of minutes in DMSO but on the order of hours in water and methanol. The rate constant was three orders of magnitude larger in DMSO than in water or methanol.

Optimisation of electrocatalytic dechlorination of 2,4-dichlorophenoxyacetic acid on a roughened silver–palladium cathode

Electrocatalytic hydrogenolysis (ECH) dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D) in an aqueous solution was investigated at room temperature using a roughened silver–palladium cathode (Pd/Ag(r) cathode) in batch-mode electrolysis experiments. The Pd/Ag(r) cathode was prepared by galvanic replacement reaction (GRR) of a roughened silver (Ag(r)) electrode with PdCl2 solution. The effect of preparation conditions on the catalytic activity and stability of the Pd/Ag(r) cathode and of operating parameters on the rate and current efficiency (CE) of the ECH dechlorination reaction were evaluated. In particular, the ECH dechlorination mechanism of 2,4-D was analysed with regard to the dependence of dechlorination efficiency on the different operating parameters. Moreover, preliminary assessments of product selectivity and carbon mass balance of the dechlorination reaction were carried out. The results demonstrate that a moderate GRR time and GRR temperature favoured the catalytic activity and cathode stability and that a basic aqueous solution without ethanol, high 2,4-D concentration, and moderate current density had the most beneficial effects on the dechlorination process. Under the optimised conditions, 25mM of 2,4-D could be selectively dechlorinated to phenoxyacetic acid with 85% yield and 66% CE at 298K after 6h electrolysis. The only products generated during the electrolysis process were phenoxyacetic acid, 2-chlorophenoxyacetic acid, and 4-chlorophenoxyacetic acid.