Ppmv CO2 Research Articles

Ocean acidification alters microeukaryotic and bacterial food web interactions in a eutrophic subtropical mesocosm

Ocean acidification (OA) is known to influence biological and ecological processes, mainly focusing on its impacts on single species, but little has been documented on how OA may alter plankton community interactions. Here, we conducted a mesocosm experiment with ambient (∼410 ppmv) and high (1000 ppmv) CO2 concentrations in a subtropical eutrophic region of the East China Sea and examined the community dynamics of microeukaryotes, bacterioplankton and microeukaryote-attached bacteria in the enclosed coastal seawater. The OA treatment with elevated CO2 affected taxa as the phytoplankton bloom stages progressed, with a 72.89% decrease in relative abundance of the protist Cercozoa on day 10 and a 322% increase in relative abundance of Stramenopile dominated by diatoms, accompanied by a 29.54% decrease in relative abundance of attached Alphaproteobacteria on day 28. Our study revealed that protozoans with different prey preferences had differing sensitivity to high CO2, and attached bacteria were more significantly affected by high CO2 compared to bacterioplankton. Our findings indicate that high CO2 changed the co-occurrence network complexity and stability of microeukaryotes more than those of bacteria. Furthermore, high CO2 was found to alter the proportions of potential interactions between phytoplankton and their predators, as well as microeukaryotes and their attached bacteria in the networks. The changes in the relative abundances and interactions of microeukaryotes between their predators in response to high CO2 revealed in our study suggest that high CO2 may have profound impacts on marine food webs.

Evaluating the viability of ethylenediamine-functionalized Mg-MOF-74 in direct air capture: The challenges of stability and slow adsorption rate

Carbon removal technologies, such as direct air capture (DAC), hold great potential in mitigating anthropogenic CO2 emissions. Amine-tethered metal-organic frameworks (MOFs) that capture CO2 selectively via chemisorption have been highlighted as frontrunners for CO2 removal technologies. To this end, ethylenediamine (ED) was employed to decorate the metal sites of Mg-MOF-74, and both bare and amine-modified frameworks were thoroughly characterized and studied for DAC using an automated fixed-bed sorption device. The material exhibited a promising CO2 capacity of up to 1.8 mmol/g from 400 ppmv CO2 in humid conditions, although the amount of adsorbed H2O was several times higher. The highest adsorption capacities were measured at 25–35 °C, while decreased capacity was observed at 12 °C due to slower adsorption rate. In dry cyclic adsorption-desorption tests, the cyclic CO2 capacity reduced slightly in 18 cycles. However, at 2 vol% humidity, the capacity dropped rapidly over successive cycles, revealing poor hydrolytic stability. Preliminary coating experiments were conducted on stainless steel plates and cordierite monoliths, suggesting that reasonably even coating layers could be achieved on these substrates with relatively simple coating techniques. High water adsorption, slow adsorption rate at low temperatures, and the rapid cyclic capacity decrease in humid conditions may limit the application of the studied adsorbent for DAC. The vital aspects of the real application of MOFs in DAC, such as adsorption kinetics and stability in humid conditions, are rarely explored in detail in the literature, and these results indicate that these aspects warrant extensive study for the development of practically applicable DAC adsorbents.

Dynamic and Steady-State Simulation Study for the Stabilization of Natural Gas Condensate and CO2 Removal through Heating and Pressure Reduction

Stabilization of condensate is a highly energy-consuming process compared to other oil and gas processes. There is a need to reduce this energy consumption. Therefore, the present work aims to simulate the stabilization unit in terms of available energy and on-spec stabilized condensate products. Natural gas condensate liquids (NGL) need to be stabilized by eliminating lighter hydrocarbon gases and acid gases before being sent to the refinery. Stabilized NGL has the vapor pressure determined as a Reid vapor pressure of 7 psia, showing that light components did not evolve as a separate gas phase. Stabilization and CO2 removal was performed through the distillation method by heating and pressure reduction using steady state and dynamic simulation through Aspen HYSYS. Different process alterations around the exchanger and column have been studied based on the utilities available for the stabilization and CO2 removal process. Sensitivity studies, including the impact of CO2 concentration, the temperature at the inlet of the stabilizer flash separator, and the dynamic simulation for the PID controller, have been performed to analyze the impact on the process parameters, such as Reid vapor pressure (RVP) and CO2 of the rundown air cooler and heat duties of the exchangers. Actual plant data have been used for the validation of process simulation values for the accuracy of the condensate stabilization unit model. Based on the scenarios analyzed, it can be concluded that the nitrogen stripping method achieved 7 ppmv CO2 and 7 psia RVP in the condensate from the cooler outlet, while a variation of 29 bpd was observed for the stabilized condensate flowrate throughout all scenarios with data validation showing 0.24% discrepancy between Aspen Hysys data and actual plant data.

Improving the performance of artificial neural networks trained on synthetic data in gas spectroscopy – a study on two sensing approaches

Abstract Artificial neural networks (ANNs) are used in quantitative infrared gas spectroscopy to predict concentrations on multi-component absorption spectra. Training of ANNs requires vast amounts of labelled training data which may be elaborate and time consuming to obtain. Additional data can be gained by the utilization of synthetically generated spectra, but at the cost of systematic deviations to measured data. Here, we present two approaches to train ANNs with a combination of comparatively small, measured data sets and synthetically generated data. For the first approach a neural network is trained hybridly with synthetically generated infrared absorption spectra of mixtures of N2O and CO and measured zero-gas spectra, taken with a mid-infrared dual comb spectrometer. This improves the mean absolute error (MAE) of the network predictions from 0.46 to 0.01 ppmV and 0.24 to 0.01 ppmV for the concentration predictions of N2O and CO respectively for zero-gas measurements which was previously observed for training with purely synthetic data. At the same time a similar performance on spectra from gas mixtures of 0–100 ppmV N2O and 0 to 60 ppmV CO was achieved. For the second approach an ANN pre-trained on synthetic infrared spectra of mixtures of acetone and ethanol is retrained on a small dataset consisting of 26 spectra taken with a mid-infrared photoacoustic spectrometer. In this case the MAE for the concentration predictions of ethanol and acetone are improved by 45 % and 20 % in comparison to purely synthetic training. This shows the capability of using synthetically generated data to train ANNs in combination with small amounts of measured data to further improve neural networks for gas sensing and the transferability between different sensing approaches.

A comprehensive evaluation of amine-impregnated silica materials for direct air capture of carbon dioxide

The potential of amine-impregnated silica materials for Direct Air Capture (DAC) of CO2 was investigated. A commercially available mesoporous silica was impregnated with tetraethylenepentamine (TEPA) and polyethylenimine (PEI) with molecular weights of 600, 1200, and 1800, each using amine loadings of 10–50 wt%. The materials were screened for equilibrium CO2 uptake, amine efficiency, and adsorption kinetics at temperatures of 25–35 °C. For all loadings, the CO2 uptakes followed the order of TEPA > PEI-600 > PEI-1200 ≈ PEI-1800. Also, for all amines, the materials synthesized with 50% loading achieved the highest equilibrium CO2 uptakes despite suffering from low amine efficiency and slow adsorption kinetics due to diffusional limitations. For these materials, increasing the adsorption temperature from 25 to 30 and 35 °C enhanced equilibrium CO2 uptake and amine efficiency, indicating kinetically controlled adsorption. In contrast, for all amines, the materials synthesized with 40% loading achieved a combination of high equilibrium CO2 uptake, good amine efficiency, and fast adsorption kinetics; therefore, they were selected to undergo 50 successive adsorption–desorption cycles. Despite an initially high CO2 uptake, TEPA suffered from low thermal stability due to its volatility, resulting in an amine loss of 55% and CO2 uptake loss of 29%. In contrast, bulkier amines such as PEI-600 outperformed TEPA, showing high thermal stability (1.4% amine loss) and low CO2 uptake loss (0.8%). Selected materials underwent column-breakthrough experiments in the presence of 400 ppmv CO2 in N2. Under dry conditions, TEPA achieved a longer breakthrough time than PEI-600 (13 versus 4 min). Under humid conditions, the breakthrough time for PEI-600 increased from 4 to 15 min, confirming previous reports that humidity boosts the CO2 uptake of amine-modified materials.

Improving measurement accuracy of CH4 and CO2 sensing system using passive locking achromatic multipass absorption cell

Highly accurate CH4 and CO2 sensing systems are required to monitor geochemical gases in the atmosphere to provide early warnings about earthquakes. Based on an achromatic model, an achromatic structure was developed in this study using ridge-shaped windows to eliminate optical system dispersion, and a passive locking structure was designed based on a multilayer rotationally symmetrical model to lock the cavity. A passive locking achromatic multipass absorption cell (PLAMAC) based on achromatic and passive locking structures was developed to improve the optical transmission performance and environmental adaptability. A temperature control subsystem was employed to lock the PLAMAC state and control the gas temperature. A gas-sensing system was developed using PLAMAC to realize highly accurate measurements of CH4 and CO2. The PLAMAC enables chromatic aberration-free transmission in the wavelength range of 1.55– 2.35 µm and achieves perfect locking at environmental temperatures from –10–40 °C. The systematic errors are 0.93‰@ 1653.7 and 0.91‰@ 2329.05 nm for 500 parts per million by volume (ppmv) CH4 and 0.92‰@ 1572.3 and 0.91‰@ 2004.5 nm for 1000 ppmv CO2 within the confidence interval of 98%. The PLAMAC system has a higher accuracy over a wide spectral range and greater environmental adaptability than the sensing system based on MAC-41. The experiments verified that the PLAMAC system has significant advantages in multi-gas exploration with wide temperature variations.

A CFD study of the effects of combined impurities, ground temperature, and topography upon the consequence distances and plume shapes generated by CO2 release from CCS pipeline failure.

In the carbon capture and storage (CCS) infrastructure, the risk of a high-pressure buried pipeline rupture possibly leads to catastrophic accidents due to the release of tremendous amounts of carbon dioxide (CO2). Therefore, it is crucial to conduct an in-depth study on CO2 atmospheric dispersion when developing CO2 pipeline. In fact, the CO2 captured from diverse industrial processes may contain a variety of impurities. The combined effect of the toxicities of the multiple impurities increases the risk, which has usually been ignored by previous studies. In this paper, computational fluid dynamics (CFD) technology is applied to investigate the influence of hazardous chemicals on CO2 stream dispersion under different meteorological, complex terrain features, and ground temperature condition. In addition, the effect of combined toxic impurities on consequence distance was also investigated comprehensively. It was found that complex conditions affected the near-surface flow field, and obstacles enhanced the lateral dispersion of CO2. Compared to 288K ground temperature, the plume area inside the 50,000 ppmv CO2 boundary decreased by 8.2%. The hazardous effects of combined toxic impurities became significant compared to a single toxic impurity. This study may furnish a viable assessment technique for the risks associated with CCS.

Fe decorated CeO2 microsphere catalyst with surface oxygen defect for NO reduction by CO

The selective catalytic reduction of nitrogen oxides (NOx) by carbon monoxide (CO-SCR) is a promising way to deal with exhaust gasses. And Effective redox cycle and NO dissociation ability are crucial factors for catalytic reduction of NOx. Herein, Fe decorated CeO2 microsphere catalysts with surface oxygen defect were synthesized by solvothermal and calcination method. Among all catalysts, 0.5Fe-CeO2 sample showed excellent catalytic performance with efficiency near 96% for NO reduction under the condition of 550 ppmv NO, 1200 ppmv CO, and 40,000 h − 1 of GHSV. It was found that Fe doping could efficiently regulate Ce4+/Ce3+ redox couple and oxygen vacancy for catalytic activity. XRD, Raman, XPS, EPR and H2-TPR etc. were employed to explore the physicochemical properties of samples. The results showed that Fe had been incorporated into CeO2 by XRD, and the results of Raman spectrum and XPS indicated that Ce4+/Ce3+ redox couple existed in 0.5Fe-CeO2 catalyst. Furthermore, the H2-TPR spectrum displayed the formation of oxygen vacancy in the samples. N2 adsorption-desorption isotherms indicated that the doping of Fe could enlarge the specific surface area, pore volume and pore dimeter of the samples, and thus greatly enhanced the NO adsorption and further NO catalytic reduction on catalysts. In addition, other characterization of physicochemical properties and density functional theory (DFT) calculation were performed to reveal the mechanism of NO + CO reaction. As a result, a mechanism was proposed to elucidate highly efficient NO reduction over the catalysts of Fe decorated CeO2 microspheres. Finally, the synergistic effects of redox center and oxygen vacancy on catalytic activity enhancement were revealed. This work provides a promising way to the design of efficient catalysts for NO reduction.

Simulated climate change, but not predation risk, accelerates Aedes aegypti emergence in a microcosm experiment in western Amazonia.

Climate change affects individual life-history characteristics and species interactions, including predator-prey interactions. While effects of warming on Aedes aegypti adults are well known, clarity the interactive effects of climate change (temperature and CO2 concentration) and predation risk on the larval stage remains unexplored. In this study, we performed a microcosm experiment simulating temperature and CO2 changes in Manaus, Amazonas, Brazil, for the year 2100. Simulated climate change scenarios (SCCS) were in accordance with the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC). Used SCCS were: Control (real-time current conditions in Manaus: average temperature is ~25.76°C ± 0.71°C and ~477.26 ± 9.38 parts per million by volume (ppmv) CO2); Light: increase of ~1,7°C and ~218 ppmv CO2; Intermediate: increase of ~2.4°C and ~446 ppmv CO2; and Extreme: increase of ~4.5°C and ~861 ppmv CO2, all increases were relative to a Control SCCS. Light, Intermediate and Extreme SCCS reproduced, respectively, the B1, A1B, and A2 climatic scenarios predicted by IPCC (2007). We analyzed Aedes aegypti larval survivorship and adult emergence pattern with a factorial design combining predation risk (control and predator presence-Toxorhynchites haemorrhoidalis larvae) and SCCS. Neither SCCS nor predation risk affected Aedes aegypti larval survivorship, but adult emergence pattern was affected by SCCS. Accordingly, our results did not indicate interactive effects of SCCS and predation risk on larval survivorship and emergence pattern of Aedes aegypti reared in SCCS in western Amazonia. Aedes aegypti is resistant to SCCS conditions tested, mainly due to high larval survivorship, even under Extreme SCCS, and warmer scenarios increase adult Aedes aegypti emergence. Considering that Aedes aegypti is a health problem in western Amazonia, an implication of our findings is that the use of predation cues as biocontrol strategies will not provide a viable means of controlling the accelerated adult emergence expected under the IPCC climatic scenarios.

Improvement of steam methane reforming via in-situ CO2 sorption over a nickel-calcium composite catalyst

Optimization of steam methane reforming (SMR) reaction by CO2 sorption enhancement was investigated. In this study, the sorption-enhanced steam methane reforming reaction (SESMR) was conducted to maximize hydrogen production via suitable adjustments in the operating conditions of the reaction, which include the molar ratio of steam to CH4, space velocity, and temperature. The reforming catalysts were prepared by a physical mixture of 20 wt% Ni/Al2O3 and CaO. The results reveal that there are significant differences in CH4 conversion between the SMR and the SESMR from 18% to 108%; this conversion strongly depended on the reaction conditions. High-purity H2 products (98.9%) with <0.1 ppmv CO were obtained by SESMR under the suitable conditions of 2600 cm3/g/h, steam/CH4 molar ratio of 4 and 823 K. This implies that the high-quality H2 produced through the SESMR process could be directly used for the proton-exchange membrane fuel cell.

Physiological and biochemical responses of Microcystis aeruginosa to phosphine (PH3) under elevated CO2

Phosphine (PH3) is an important factor driving the outbreak of cyanobacterial blooms that produce toxic microcystin threating human health. To clarify the physiological and biochemical responses of cyanobacteria to PH3 under elevated CO2 concentration, Microcystis aeruginosa was used in the coupling treatment of 1000 ppmv CO2 and PH3 at different concentrations respectively. The chlorophyll a (Chl-a), carotenoid, net photosynthetic rate and total protein of M. aeruginosa exhibited evidently increasing tendency under the coupling treatment of 1000 ppmv CO2 and PH3 at different concentrations (7.51 × 10−3, 2.48 × 10−2, 7.51 × 10−2 mg/L). The coupling treatments resulted in the higher concentrations of Chl-a and carotenoid of M. aeruginosa, compared to those in the control and the treatment with CO2 alone, and their enhancement increased with the increase in PH3 concentrations. The total antioxidant capacity (T-AOC) in the coupling treatment with CO2 and PH3 of 2.48 × 10−2 mg/L and 7.51 × 10−3 mg/L showed increasing tendency, compared to the treatment with PH3 alone. Additionally, the coupling treatment with 1000 ppmv CO2 and PH3 also altered the pH and DO level in the culture medium. In this regard, the coupling treatment with CO2 and PH3 at an appropriate concentration can enhance the resistance of M. aeruginosa to PH3 toxicity and is beneficial to the reproduction of M. aeruginosa, presumably resulting in potential for the outbreak of cyanobacteria bloom. Given the concern about global warming and the increase in atmospheric CO2 level, our research laid a foundation for the scientific understanding of the correlation between PH3 and cyanobacteria blooms.

Chemical and Noble Gas Isotope Compositions of Formation Gases from a 3 km Deep Scientific Borehole in the Koyna Seismogenic Zone, Western India

A 3 km deep research borehole KFD1 was drilled in the Koyna reservoir-triggered seismicity region, Western India, between December 2016 and May 2017. The 1967M6.3 Koyna earthquake had generated a NNE-SSW trending surface fissure zone in the Nanel-Donichawadi-Kadoli sector. KFD1 is located ~5 km south of Kadoli along the trend of the Donichawadi fault zone. Online gas monitoring was carried out during drilling of KFD1 from 1315 m to 2831 m depth to sample and study the composition of crustal gases. Formation gases CO2, CH4, H2, and He were only observed during water flushing of ~100 m intervals following coring runs. Laboratory analyses of gas samples collected between 1737 m and 2831 m depth revealed concentrations of up to 1200 ppmv CO2, 186 ppmv CH4, 139 ppmv H2, and 12.8 ppmv He. Zones enriched in gases are mostly below the 2100 m depth with significant He enhancement ranging from 4.6 to 7.6 ppmv above the atmospheric value. The He-rich zones correlate well with the zones of anomalous physical and mechanical properties identified from geophysical logs and are characterized by high fracture density as revealed from borehole images, indicating that the borehole punctured multiple fracture zones. The helium concentrations are consistent with those previously observed over the surface fissures near Kadoli, suggesting a southward extension of the Donichawadi fault zone up to the KFD1 site and confirming that the fault zone is permeable even after 50 years of the 1967 Koyna earthquake.3He/4He ratios of eleven gas samples fall between0.426±0.022and0.912±0.059 Ra, with4He/20Ne values between0.3449±0.0091and0.751±0.020. Air-corrected helium isotope ratios indicate that helium is a mixture of atmospheric and crustal radiogenic components but no mantle contribution within 2σanalytical uncertainties.

Diode laser photoacoustic spectroscopy of CO2, H2S and O2 in a differential Helmholtz resonator for trace gas analysis in the biosciences and petrochemistry

Photoacoustic spectroscopy in a differential Helmholtz resonator has been employed with near-IR and red diode lasers for the detection of CO2, H2S and O2 in 1 bar of air/N2 and natural gas, in static and flow cell measurements. With the red distributed feedback (DFB) diode laser, O2 can be detected at 764.3 nm with a noise equivalent detection limit of 0.60 mbar (600 ppmv) in 1 bar of air (35-mW laser, 1-s integration), corresponding to a normalised absorption coefficient α = 2.2 × 10−8 cm−1 W s1/2. Within the tuning range of the near-IR DFB diode laser (6357–6378 cm−1), CO2 and H2S absorption features can be accessed, with a noise equivalent detection limit of 0.160 mbar (160 ppmv) CO2 in 1 bar N2 (30-mW laser, 1-s integration), corresponding to a normalised absorption coefficient α = 8.3 × 10−9 cm−1 W s1/2. Due to stronger absorptions, the noise equivalent detection limit of H2S in 1 bar N2 is 0.022 mbar (22 ppmv) at 1-s integration time. Similar detection limits apply to trace impurities in 1 bar natural gas. Detection limits scale linearly with laser power and with the square root of integration time. At 16-s total measurement time to obtain a spectrum, a noise equivalent detection limit of 40 ppmv CO2 is obtained after a spectral line fitting procedure, for example. Possible interferences due to weak water and methane absorptions have been discussed and shown to be either negligible or easy to correct. The setup has been used for simultaneous in situ monitoring of O2, CO2 and H2S in the cysteine metabolism of microbes (E. coli), and for the analysis of CO2 and H2S impurities in natural gas. Due to the inherent signal amplification and noise cancellation, photoacoustic spectroscopy in a differential Helmholtz resonator has a great potential for trace gas analysis, with possible applications including safety monitoring of toxic gases and applications in the biosciences and for natural gas analysis in petrochemistry.Graphical abstract

Efficient photocatalytic oxidation of gaseous toluene over F-doped TiO2 in a wet scrubbing process

The application of photocatalytic oxidation (PCO) of volatile organic compounds (VOCs) is strongly limited by catalyst deactivation, low mineralization ability and mass-transfer in gas-solid phase. Wet-scrubbing coupled with PCO (WPCO) provides a novel and efficient method for VOCs degradation. Fluorine-doped TiO2 (F-TiO2) photocatalyst was prepared and applied in this coupled process for toluene degradation. Toluene removal efficiency reached 80% over F-TiO2, while it was only 25% over TiO2 in the WPCO process. As for gas-solid PCO process, F-TiO2 had a low toluene removal efficiency of 10%. Furthermore, the mineralization capability of WPCO process over F-TiO2 also remarkably increased, achieving about 92 ppmv CO2 generated from toluene oxidation. Compared with TiO2, the surface fluorinated TiO2 significantly enhanced toluene degradation since it generated mobile hydroxyl radical (OH) in the WPCO process. The F/Ti molar ratio (RF) greatly affected photocatalytic activity towards toluene degradation, and the F-TiO2 with RF at 1 obtained the best performance. The photocatalytic activity of F-TiO2 had good stability and remained highly efficient after four runs.

Insights Into the Mechanisms of Phreatic Eruptions From Continuous High Frequency Volcanic Gas Monitoring: Rincón de la Vieja Volcano, Costa Rica

Rincon de la Vieja (10.49 N, 85.19 W), the northernmost active volcano in Costa Rica, hosts a hot acidic crater lake, which frequently produces large phreatic to phreatomagmatic eruptions. Relatively little is known about this volcano, as it is poorly monitored due to remote location and difficulty of access. In February-May 2017, we deployed a Multi-GAS instrument to continuously monitor gas concentrations in the plume released by the vigorously degassing crater lake. The Multi-GAS station registered gas information from February 3 to May 9, 2017, a period during which many phreatic to phreatomagmatic eruptions occurred, 42 of which were recorded seismically. Nine of these eruptions were also registered in the Multi-GAS record as distinct gas pulses, representing the first measurements of gases explosively released during individual phreatic/phreatomagmatic explosions. Our results show that during background quiescent degassing the Rincon de la Vieja crater lake plume was characterized by high CO2/SO2 ratios (64±59) and H2S/SO2 ratios of 0.57±0.20. This composition is interpreted as reflecting hydrothermal (re)processing of magma-sourced gas in the sub-limnic environment. Phreatic blasts were recorded by the Multi-GAS as brief (1-2 minutes long) pulses of elevated gas mixing ratios (up to ~ 52 ppmv SO2 and > 3000 ppmv CO2), or more than an order of magnitude higher than during background degassing (~ 1 ppmv SO2 and ~ 450 ppmv CO2). During the phreatic eruption(s), the H2S/SO2 ratio was systematically lower (<0.18) than during background degassing, but the CO2/SO2 ratio remained high (and variable), ranging from 37 to 390. These compositions indicate a S-poor eruptive gas, suggesting that the source magmatic gas is extensively processed during pre-eruptive hydrothermal storage, most likely by native S deposition and by sulfate formation. Our gas results are thus overall consistent with a mechanism of phreatic eruptions triggered by accumulation of magmatic-hydrothermal gases beneath a hydrothermal system. We conclude that real-time Multi-GAS monitoring can provide key insights into the mechanisms driving phreatic eruptions at Rincon de la Vieja, and perhaps at other similar volcanic lakes.

Primary emissions of glyoxal and methylglyoxal from laboratory measurements of open biomass burning

Abstract. We report the emissions of glyoxal and methylglyoxal from the open burning of biomass during the NOAA-led 2016 FIREX intensive at the Fire Sciences Laboratory in Missoula, MT. Both compounds were measured using cavity-enhanced spectroscopy, which is both more sensitive and more selective than methods previously used to determine emissions of these two compounds. A total of 75 burns were conducted, using 33 different fuels in 8 different categories, providing a far more comprehensive dataset for emissions than was previously available. Measurements of methylglyoxal using our instrument suffer from spectral interferences from several other species, and the values reported here are likely underestimates, possibly by as much as 70 %. Methylglyoxal emissions were 2–3 times higher than glyoxal emissions on a molar basis, in contrast to previous studies that report methylglyoxal emissions lower than glyoxal emissions. Methylglyoxal emission ratios for all fuels averaged 3.6±2.4 ppbv methylglyoxal (ppmv CO)−1, while emission factors averaged 0.66±0.50 g methylglyoxal (kg fuel burned)−1. Primary emissions of glyoxal from biomass burning were much lower than previous laboratory measurements but consistent with recent measurements from aircraft. Glyoxal emission ratios for all fuels averaged 1.4±0.7 ppbv glyoxal (ppmv CO)−1, while emission factors averaged 0.20±0.12 g glyoxal (kg fuel burned)−1, values that are at least a factor of 4 lower than assumed in previous estimates of the global glyoxal budget. While there was significant variability in the glyoxal emission ratios and factors between the different fuel groups, glyoxal and formaldehyde were highly correlated during the course of any given fire, and the ratio of glyoxal to formaldehyde, RGF, was consistent across many different fuel types, with an average value of 0.068±0.018. While RGF values for fresh emissions were consistent across many fuel types, further work is required to determine how this value changes as the emissions age.

Nitrous oxide from chemodenitrification: A possible missing link in the Proterozoic greenhouse and the evolution of aerobic respiration.

The potent greenhouse gas nitrous oxide (N2 O) may have been an important constituent of Earth's atmosphere during Proterozoic (~2.5-0.5Ga). Here, we tested the hypothesis that chemodenitrification, the rapid reduction of nitric oxide by ferrous iron, would have enhanced the flux of N2 O from ferruginous Proterozoic seas. We empirically derived a rate law, , and measured an isotopic site preference of +16‰ for the reaction. Using this empirical rate law, and integrating across an oceanwide oxycline, we found that low nM NO and μM-low mM Fe2+ concentrations could have sustained a sea-air flux of 100-200 Tg N2 O-Nyear-1 , if N2 fixation rates were near-modern and all fixed N2 was emitted as N2 O. A 1D photochemical model was used to obtain steady-state atmospheric N2 O concentrations as a function of sea-air N2 O flux across the wide range of possible pO2 values (0.001-1 PAL). At 100-200 Tg N2 O-Nyear-1 and >0.1 PAL O2 , this model yielded low-ppmv N2 O, which would produce several degrees of greenhouse warming at 1.6ppmv CH4 and 320ppmv CO2 . These results suggest that enhanced N2 O production in ferruginous seawater via a previously unconsidered chemodenitrification pathway may have helped to fill a Proterozoic "greenhouse gap," reconciling an ice-free Mesoproterozoic Earth with a less luminous early Sun. A particularly notable result was that high N2 O fluxes at intermediate O2 concentrations (0.01-0.1 PAL) would have enhanced ozone screening of solar UV radiation. Due to rapid photolysis in the absence of an ozone shield, N2 O is unlikely to have been an important greenhouse gas if Mesoproterozoic O2 was 0.001 PAL. At low O2 , N2 O might have played a more important role as life's primary terminal electron acceptor during the transition from an anoxic to oxic surface Earth, and correspondingly, from anaerobic to aerobic metabolisms.

Assessing historical and projected carbon balance of Alaska: A synthesis of results and policy/management implications.

We summarize the results of a recent interagency assessment of land carbon dynamics in Alaska, in which carbon dynamics were estimated for all major terrestrial and aquatic ecosystems for the historical period (1950-2009) and a projection period (2010-2099). Between 1950 and 2009, upland and wetland (i.e., terrestrial) ecosystems of the state gained 0.4TgC/yr (0.1% of net primary production, NPP), resulting in a cumulative greenhouse gas radiative forcing of 1.68×10-3 W/m2 . The change in carbon storage is spatially variable with the region of the Northwest Boreal Landscape Conservation Cooperative (LCC) losing carbon because of fire disturbance. The combined carbon transport via various pathways through inland aquatic ecosystems of Alaska was estimated to be 41.3TgC/yr (17% of terrestrial NPP). During the projection period (2010-2099), carbon storage of terrestrial ecosystems of Alaska was projected to increase (22.5-70.0TgC/yr), primarily because of NPP increases of 10-30% associated with responses to rising atmospheric CO2 , increased nitrogen cycling, and longer growing seasons. Although carbon emissions to the atmosphere from wildfire and wetland CH4 were projected to increase for all of the climate projections, the increases in NPP more than compensated for those losses at the statewide level. Carbon dynamics of terrestrial ecosystems continue to warm the climate for four of the six future projections and cool the climate for only one of the projections. The attribution analyses we conducted indicated that the response of NPP in terrestrial ecosystems to rising atmospheric CO2 (~5% per 100 ppmv CO2 ) saturates as CO2 increases (between approximately +150 and +450 ppmv among projections). This response, along with the expectation that permafrost thaw would be much greater and release large quantities of permafrost carbon after 2100, suggests that projected carbon gains in terrestrial ecosystems of Alaska may not be sustained. From a national perspective, inclusion of all of Alaska in greenhouse gas inventory reports would ensure better accounting of the overall greenhouse gas balance of the nation and provide a foundation for considering mitigation activities in areas that are accessible enough to support substantive deployment.

Oligocene climate signals and forcings in Eurasia revealed by plant macrofossil and modelling results

The Oligocene represents a transitional time period from a warm climate to a cooler climate that is more representative of the modern day; yet, a general view of continental climate pattern and forcings are still lacking. Different proxies and models show striking disparities, especially in mid-high latitudes, requiring validation of Oligocene climate reconstruction in order to understand the large-scale processes that drive the observed climate changes. Here, we compiled 149 macrofossil floras in the mid-high latitudes of Eurasia, then quantitatively reconstructed the Oligocene climate using Coexistence Approach (CA) and combined previously published paleoclimate data. During the Oligocene, Eurasian mid-high latitudes were mainly dominated by a humid subtropical climate. Mean annual temperature (MAT) ranged between 5.4 °C and 25.5 °C with mean annual precipitation (MAP) ranging from 338 to 2453 mm. Three regions (Europe, central Eurasia and eastern Asia) indicate different climatic regimes, with a generally warmer and wetter climate in Europe and a colder and drier climate in central Eurasia when compared to eastern Asia. No significant reorganization of climate was observed between the Early and Late Oligocene. The climate anomalies between the Oligocene and present indicate that geographic changes (e.g. retreat of the Paratethys Sea) played an important role in shaping the climate pattern of Eurasia. By comparing the fossil data to a range of different HadCM3L model simulations of the Oligocene with differing boundary conditions (e.g. CO2 and topography), we demonstrate similar large-scale climate spatial patterns between models and fossil data, however, models simulated much higher temperature seasonality (lower simulated winter temperatures and higher simulated summer temperatures) in Eurasia. Mean annual temperature analysis indicates that simulations with 560 and 1120 ppmv CO2 matched better with fossil data when compared to other simulations, depending on the topography. These results provide some constraints that should be considered for future paleoclimate modelling.

Effect of elevated CO2 on Vigna radiata and two weed species: yield, physiology and crop–weed interaction

A field experiment was conducted in a free-air CO2 enrichment (FACE) facility to investigate the effect of elevated atmospheric CO2 on growth and physiology of green gram (Vigna radiata (L.) R.Wilczek) and associated weed species (Euphorbia geniculata Ortega and Commelina diffusa Burm.f.). Physiological and reproductive behaviour and interaction of the crop and two weed species under elevated CO2 was also studied. Plants were grown under ambient (390 ± 5 ppmv) and elevated (550 ± 50 ppmv) CO2. The results showed that growth, photosynthesis and carbonic anhydrase activity increased in all the test species. Stomatal conductance and transpiration decreased in V. radiata (5.1% and 30.5%, respectively) and C. diffusa (19% and 13.7%) but increased in E. geniculata (6.5% and 27.6%), suggesting a unique adaptive potential of E. geniculata at elevated CO2. Higher accumulation of reactive oxygen species (hydrogen peroxide and superoxide) was noticed at elevated CO2 in V. radiata than in E. geniculata and C. diffusa. Potential of E. geniculata to maintain redox homeostasis in its original state may provide an advantage over two other species in adaptation to climate change. Isoenzyme patterns of superoxide dismutase and stronger activity of antioxidant enzymes suggest species-specific differential regulation and induction of new isoforms under elevated CO2. Enrichment of atmospheric CO2 at a competitive density of weeds lowered the yield (12.12%) and quality of green gram seed, with diminished protein content (16.14% at ambient CO2 to 15.42% at elevated CO2) and enhanced carbohydrate content (3.11%). From the study, it may be concluded that a rise in atmospheric CO2 concentration affects plant performance in a species-specific manner. Among the three species, E. geniculata emerged as most responsive to elevated CO2, showing higher transpiration and stomatal conductance and a stronger antioxidant defence system in a higher CO2 atmosphere. At elevated CO2, weed–crop interaction altered in favour of weeds leading to considerable yield loss of green gram seed.