Surface CO2 Concentrations Research Articles

PAPILA dataset: a regional emission inventory of reactive gases for South America based on the combination of local and global information

Abstract. The multidisciplinary project Prediction of Air Pollution in Latin America and the Caribbean (PAPILA) is dedicated to the development and implementation of an air quality analysis and forecasting system to assess pollution impacts on human health and economy. In this context, a comprehensive emission inventory for South America was developed on the basis of the existing data on the global dataset CAMS-GLOB-ANT v4.1 (developed by joining CEDS trends and EDGAR v4.3.2 historical data), enriching it with data derived from locally available emission inventories for Argentina, Chile, and Colombia. This work presents the results of the first joint effort of South American researchers and European colleagues to generate regional maps of emissions, together with a methodological approach to continue incorporating information into future versions of the dataset. This version of the PAPILA dataset includes CO, NOx, NMVOCs, NH3, and SO2 annual emissions from anthropogenic sources for the period 2014–2016, with a spatial resolution of 0.1∘ × 0.1∘ over a domain that covers 32–120∘ W and 34∘ N–58∘ S. The PAPILA dataset is presented as netCDF4 files and is available in an open-access data repository under a CC-BY 4 license: https://doi.org/10.17632/btf2mz4fhf.3 (Castesana et al., 2021). A comparative assessment of PAPILA–CAMS datasets was carried out for (i) the South American region, (ii) the countries with local data (Argentina, Colombia, and Chile), and (iii) downscaled emission maps for urban domains with different environmental and anthropogenic factors. Relevant differences were found at both country and urban levels for all the compounds analyzed. Among them, we found that when comparing PAPILA total emissions versus CAMS datasets at the national level, higher levels of NOx and considerably lower levels of the other species were obtained for Argentina, higher levels of SO2 and lower levels of CO and NOx for Colombia, and considerably higher levels of CO, NMVOCs, and SO2 for Chile. These discrepancies are mainly related to the representativeness of local practices in the local emission estimates, to the improvements made in the spatial distribution of the locally estimated emissions, or to both. Both datasets were evaluated against surface concentrations of CO and NOx by using them as input data to the WRF-Chem model for one of the analyzed domains, the metropolitan area of Buenos Aires, for summer and winter of 2015. PAPILA-based modeling results had a smaller bias for CO and NOx concentrations in winter while CAMS-based results for the same period tended to deliver an underestimation of these concentrations. Both inventories exhibited similar performances for CO in summer, while the PAPILA simulation outperformed CAMS for NOx concentrations. These results highlight the importance of refining global inventories with local data to obtain accurate results with high-resolution air quality models.

Effect of Cations and Anions in the Electrolyte on CO2 electroreduction over Cu Catalysts

CO2 electroreduction has been reported as a promising method to reduce the CO2 level in the atmosphere as well as producing valuable products. Aqueous electrolytes have been reported as the most common solutions for CO2ER due to their low cost, abundance and eco-friendliness. However, CO2 electroreduction in aqueous electrolytes is not efficient enough due to the presence of the competing hydrogen evolution reaction (HER). Among techniques to improve the catalytic performance in CO2ER, electrolyte design has attracted considerable attention. Electrolyte additives such as salts or ionic liquids (ILs) can alter the surface CO2 concentration or the intermediates stability on the surface. In this study, the effect of cations and anions of additives on CO2electroreduction over copper in aqueous electrolytes has been investigated.Buffer electrolytes containing 10 mM ofsodium (Na+) or 1-butyl-3-methylimidazolium [BMIM]+ as cation and bis(trifluoromethylsulfonyl)imide [NTF2]- or dicyanamide [DCA]- as anion were added to 0.1 M KHCO3. Electrochemical impedance spectroscopy (EIS) showed that both cations and anions impact the solution resistance and charge transfer resistance. Comparing to [BMIM]+ containing electrolytes, Na-based salts showed a lower solution resistance due to the small size of Na+ions and their high conductivity. However, the charge transfer resistance is more impacted by the anion nature. DCA salts showed a lower charge transfer resistance compared to NTF2salts. The selectivity results showed that NTF2-based electrolytes showed a high faradaic efficiency (FE%) for formate probably due to high hydrophobicity and CO2 absorption capacity of the NTF2-salts. Maximum FE (38.7%) for formate was observed for [BMIM][NTF2]. In addition to the anion effect, this can be due to the interactions of [BMIM]+ with CO2 molecules and stabilizing the intermediates on the surface. In contrast, [DCA]-based salts showed a high FE for hydrogen and a very low FE for hydrocarbons even at high overpotentials. We attributed this observation to the strongly adsorption of [DCA]- on the surface. X-ray photoelectron spectroscopy (XPS) also confirmed the strong adsorption of the [DCA]- anions on the surface. Strongly adsorbed DCA ions on the surface can promote hydrogen evolution reaction, destabilize the intermediates and suppress CO2ER. In-situ electrochemical quartz crystal microbalance (EQCM) also showed a higher mass loss for DCA-salts probably due to the displacement of water molecules by ions. This study showed that additives can significantly alter the selectivity and activity in CO2ER in aqueous electrolytes.

Understanding the Increasing Hot Extremes over the Northern Extratropics Using Community Atmosphere Model

The past four decades have seen an increase of terrestrial hot extremes during summer in the northern extratropics, accompanied by the Northern Hemisphere (NH) sea surface temperature (SST) warming (mainly over 10°–70°N, 0°–360°) and CO2 concentration rising. This study aims to understand possible causes for the increasing hot extremes, which are defined on a daily basis. We conduct a series of numerical experiments using the Community Atmosphere Model version 5 model for two periods, 1979–1995 and 2002–2018. The experiment by changing the CO2 concentration only with the climatological SST shows less increase of hot extremes days than that observed, whereas that by changing the NH SST (over 10°–70°N, 0°–360°) with constant CO2 concentration strengthens the hot extremes change over mid-latitudes. The experiment with both SST and CO2 concentration changes shows hot extremes change closer to the observation compared to the single-change experiments, as well as more similar simulations of atmospheric circulations and feedbacks from cloud and radiative processes. Also discussed are roles of natural variability (e.g., Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation) and other factors (e.g., Arctic sea ice and tropical SST).

Atmospheric and Surface Seawater CO2 Measurements on R/V ISABU in the Western North Pacific in the Summer of 2018

The ocean takes up approximately 24% of anthropogenic carbon dioxide (CO<sub>2</sub>) emitted into the atmosphere in a year. The oceanic CO<sub>2</sub> uptake shows regional and seasonal differences depending on physical and chemical characteristics of seawater and biological activities (such as CO<sub>2</sub> fixation). In the tropical Western North Pacific, the surface water temperature is high, the supply of deep water is limited, and tropical cyclones usually pass in summer. We investigated atmospheric and sea surface CO<sub>2</sub> concentrations in this area using the continuous underway pCO2 measuring system equipped on the Research Vessel ISABU of Korea Institute of Ocean Science and Technology for about 21 days from August 29 to September 19, 2018. During the cruise, 9,367 CO<sub>2</sub> data were obtained from this measuring system with temperature, salinity, and GPS information. Higher CO<sub>2</sub> concentrations of the surface seawater than those of the atmosphere were observed in the areas of 22°N-23.5°N and 29°N-35°N where CO<sub>2</sub> was emitted into the atmosphere, while most of the areas between 17.5°N and 20.5°N were sinks for the atmospheric CO<sub>2</sub>. This dataset can be used for future research on the distribution of partial pressure of carbon dioxide over the global ocean surface.

Spatiotemporal Variations and Uncertainty in Crop Residue Burning Emissions over North China Plain: Implication for Atmospheric CO2 Simulation

Large uncertainty exists in the estimations of greenhouse gases and aerosol emissions from crop residue burning, which could be a key source of uncertainty in quantifying the impact of agricultural fire on regional air quality. In this study, we investigated the crop residue burning emissions and their uncertainty in North China Plain (NCP) using three widely used methods, including statistical-based, burned area-based, and fire radiative power-based methods. The impacts of biomass burning emissions on atmospheric carbon dioxide (CO2) were also examined by using a global chemical transport model (GEOS-Chem) simulation. The crop residue burning emissions were found to be high in June and followed by October, which is the harvest times for the main crops in NCP. The estimates of CO2 emission from crop residue burning exhibits large interannual variation from 2003 to 2019, with rapid growth from 2003 to 2012 and a remarkable decrease from 2013 to 2019, indicating the effects of air quality control plans in recent years. Through Monte Carlo simulation, the uncertainty of each estimation was quantified, ranging from 20% to 70% for CO2 emissions at the regional level. Concerning spatial uncertainty, it was found that the crop residue burning emissions were highly uncertain in small agricultural fire areas with the maximum changes of up to 140%. While in the areas with large agricultural fire, i.e., southern parts of NCP, the coefficient of variation mostly ranged from 30% to 100% at the gridded level. The changes in biomass burning emissions may lead to a change of surface CO2 concentration during the harvest times in NCP by more than 1.0 ppmv. The results of this study highlighted the significance of quantifying the uncertainty of biomass burning emissions in a modeling study, as the variations of crop residue burning emissions could affect the emission-driven increases in CO2 and air pollutants during summertime pollution events by a substantial fraction in this region.

Effect of Cobalt Oxides on the Catalytic Combustion of Odor.

The catalytic combustion of acetaldehyde was studied using various types of Co oxides and Co-PC. The Co oxides and Co-PC were characterized using an X-ray diffractometer (XRD), X-ray photo-electron spectroscopy (XPS), and a particle sizing analyzer. The Co-PC and CoO were converted into Co₃O₄ under an air atmosphere at 450 °C, and the results were confirmed using the XRD and XPS. According to the pretreatment of the Co-PC and Co oxides, the conversion of acetaldehyde increased. The order of particle size for both fresh and pretreated samples is summarized as follows: CoO < Co-PC < Co3O4 powder < Co₃O₄ (99.995%). For all samples, acetaldehyde was not observed at temperatures above 320 °C owing to complete combustion. The conversion of acetaldehyde in the samples was affected by the fresh state of the Co oxides and the space velocity. The catalytic activity depended on the chemical state of the Co oxides and the surface concentrations of Co, O, and N.

Analysis of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; spatio-temporal variations in China using a weather–biosphere online coupled model

Abstract. The dynamics of atmospheric CO2 has received considerable attention in the literature, yet significant uncertainties remain within the estimates of contribution from the terrestrial flux and the influence of atmospheric mixing. In this study we apply the WRF-Chem model configured with the Vegetation Photosynthesis and Respiration Model (VPRM) option for biomass fluxes in China to characterize the dynamics of CO2 in the atmosphere. The online coupled WRF-Chem model is able to simulate biosphere processes (photosynthetic uptake and ecosystem respiration) and meteorology in one coordinate system. We apply WRF-Chem for a multi-year simulation (2016–2018) with integrated data from a satellite product, flask samplings, and tower measurements to diagnose the spatio-temporal variations of CO2 fluxes and concentrations in China. We find that the spatial distribution of CO2 was dominated by anthropogenic emissions, while its seasonality (with maxima in April 15 ppmv higher than minima in August) was dominated by the terrestrial flux and background CO2. Observations and simulations revealed a consistent increasing trend in column-averaged CO2 (XCO2) of 2.46 ppmv (0.6 % yr−1) resulting from anthropogenic emission growth and biosphere uptake. WRF-Chem successfully reproduced ground-based measurements of surface CO2 concentration with a mean bias of −0.79 ppmv and satellite-derived XCO2 with a mean bias of 0.76 ppmv. The model-simulated seasonality was also consistent with observations, with correlation coefficients of 0.90 and 0.89 for ground-based measurements and satellite data, respectively. Tower observations from a background site at Lin'an (30.30∘ N, 119.75∘ E) revealed a strong correlation (−0.98) between vertical CO2 and temperature gradients, suggesting a significant influence of boundary layer thermal structure on the accumulation and depletion of atmospheric CO2.

Heterogeneous responses of lake CO2 to nutrients and warming in perialpine lakes imprinted in subfossil cladoceran δ13C values

Global change transforms processes regulating carbon dioxide (CO2) concentrations in lakes, yet our understanding of the broad-scale responses of lake CO2 to global and local human perturbation across heterogeneous landscapes and multidecadal time scales is limited. We examined decadal variability in the carbon isotope (δ13C) composition of subfossil zooplankton (Branchiopoda: Cladocera) in seven large clear perialpine lakes, including three previously studied sites, to decipher different patterns in summer surface CO2 concentrations. Generalized additive models were used to examine whether and how these patterns connect to changing nutrient regimes and anthropogenic warming over the past century. In all but one of the lakes shifts in cladoceran δ13C values coincided with turning points in the eutrophication history, broadly implying decreasing summer surface CO2 concentrations driven by phosphorus fertilization of pelagic primary production. Yet where nutrient concentrations remained below mesotrophic levels, the positive relationship between δ13C and phosphorus diminished indicating that the strong biotic control of CO2 concentrations was overwritten, probably by catchment inorganic carbon inputs and internal biochemical processes. Even under extensive nutrient loading, the connection was further weakened in lakes with high catchment to lake area ratio attributable to increased catchment interference and shorter water residence times. Warming of the perialpine region was also imprinted in the isotope records, yet the temperature effects appeared modest and were restricted to three smaller lakes with lower drainage ratios. In these lakes, warming contributed to declining cladoceran δ13C values likely partially driven by epilimnetic deepening increasing CO2 in surface waters. Overall, our results manifest the broad heterogeneity of lake responses to global change and point to the importance of hydrogeomorphic context in shaping the sensitivity and responses of lake CO2 to changing nutrient regimes and warming at the regional scale.

Estimating daily full-coverage near surface O3, CO, and NO2 concentrations at a high spatial resolution over China based on S5P-TROPOMI and GEOS-FP

The Near Surface Concentrations (NSC) of O3, CO, and NO2 are crucial worldwide indicators of air quality. However, current frameworks devised for the estimation of the NSC of O3, CO, and NO2 have defects, such as coarse spatial resolution and large missing coverage. To address this issue, this study aims to estimate the daily (~13:30 local time) full-coverage NSC of O3, CO, and NO2 at a high spatial resolution (0.05° for O3 and NO2; 0.07° for CO) over China by using datasets from S5P-TROPOMI and GEOS-FP. In specific, the light gradient boosting machine is employed to train the estimation models. Validation results show that the NSC of O3, CO, and NO2 are well estimated, with the R2s of 0.91, 0.71, and 0.83 for the sample-based cross validation, respectively. Meanwhile, the proposed framework achieves a satisfactory performance in comparison to the latest related works, as reflected by the estimation accuracy and spatial resolution. As for the mapping, the estimated results show coherent spatial distribution and can accurately grasp the seasonal characteristics of each air pollutant. Finally, the estimated results are utilized to analyze the temporal variations of O3, CO, and NO2 during the COrona VIrus Disease 2019 (COVID-19) lockdown in China, which is an extend application for adopting the proposed framework in air quality monitoring. Results show that the estimated NSC of O3, CO, and NO2 in 2020 present significant variations during different periods of the COVID-19 lockdown in China compared to last year. In addition, the variations in the NSC of O3, CO, and NO2 during the COVID-19 lockdown in China possibly result from restrictions in the anthropogenic activities.

Carbon Material and Cobalt-Substitution Effects in the Electrochemical Behavior of LaMnO3 for ORR and OER.

LaMn1−xCoxO3 perovskites were synthesized by a modified sol-gel method which incorporates EDTA. These materials’ electrochemical activity towards both oxygen reduction (ORR) and oxygen evolution reactions (OER) was studied. The cobalt substitution level determines some physicochemical properties and, particularly, the surface concentration of Co and Mn’s different oxidation states. As a result, the electroactivity of perovskite materials can be tuned using their composition. The presence of cobalt at low concentration influences the catalytic activity positively, and better bifunctionality is attained. As in other perovskites, their low electrical conductivity limits their applicability in electrochemical devices. It was found that the electrochemical performance improved significantly by physically mixing with a mortar the active materials with two different carbon black materials. The existence of a synergistic effect between the electroactive component and the carbon material was interpreted in light of the strong carbon–oxygen–metal interaction. Some mixed samples are promising electrocatalysts towards both ORR and OER.

Elevated sources of cobalt in the Arctic Ocean

Abstract. Cobalt (Co) is an important bioactive trace metal that is the metal cofactor in cobalamin (vitamin B12) which can limit or co-limit phytoplankton growth in many regions of the ocean. Total dissolved and labile Co measurements in the Canadian sector of the Arctic Ocean during the U.S. GEOTRACES Arctic expedition (GN01) and the Canadian International Polar Year GEOTRACES expedition (GIPY14) revealed a dynamic biogeochemical cycle for Co in this basin. The major sources of Co in the Arctic were from shelf regions and rivers, with only minimal contributions from other freshwater sources (sea ice, snow) and eolian deposition. The most striking feature was the extremely high concentrations of dissolved Co in the upper 100 m, with concentrations routinely exceeding 800 pmol L−1 over the shelf regions. This plume of high Co persisted throughout the Arctic basin and extended to the North Pole, where sources of Co shifted from primarily shelf-derived to riverine, as freshwater from Arctic rivers was entrained in the Transpolar Drift. Dissolved Co was also strongly organically complexed in the Arctic, ranging from 70 % to 100 % complexed in the surface and deep ocean, respectively. Deep-water concentrations of dissolved Co were remarkably consistent throughout the basin (∼55 pmol L−1), with concentrations reflecting those of deep Atlantic water and deep-ocean scavenging of dissolved Co. A biogeochemical model of Co cycling was used to support the hypothesis that the majority of the high surface Co in the Arctic was emanating from the shelf. The model showed that the high concentrations of Co observed were due to the large shelf area of the Arctic, as well as to dampened scavenging of Co by manganese-oxidizing (Mn-oxidizing) bacteria due to the lower temperatures. The majority of this scavenging appears to have occurred in the upper 200 m, with minimal additional scavenging below this depth. Evidence suggests that both dissolved Co (dCo) and labile Co (LCo) are increasing over time on the Arctic shelf, and these limited temporal results are consistent with other tracers in the Arctic. These elevated surface concentrations of Co likely lead to a net flux of Co out of the Arctic, with implications for downstream biological uptake of Co in the North Atlantic and elevated Co in North Atlantic Deep Water. Understanding the current distributions of Co in the Arctic will be important for constraining changes to Co inputs resulting from regional intensification of freshwater fluxes from ice and permafrost melt in response to ongoing climate change.

Dynamic partitioning of tropical Indian Ocean surface waters using ocean colour data — management and modelling applications

Over the past few decades, partitioning of the surface ocean into ecologically-meaningful spatial domains has been approached using a range of data types, with the aim of improving our understanding of open ocean processes, supporting marine management decisions and constraining coupled ocean-biogeochemical models. The simplest partitioning method, which could provide low-latency information for managers at low cost, remains a purely optical classification based on ocean colour remote sensing. The question is whether such a simple approach has value. Here, the efficacy of optical classifications in constraining physical variables that modulate the epipelagic environment is tested for the tropical Indian Ocean, with a focus on the Chagos marine protected area (MPA). Using remote sensing data, it was found that optical classes corresponded to distinctive ranges of wind speed, wind stress curl, sea surface temperature, sea surface slope, sea surface height anomaly and geostrophic currents (Kruskal–Wallis and post-hoc Tukey honestly significantly different tests, α = 0.01). Between-class differences were significant for a set of sub-domains that resolved zonal and meridional gradients across the MPA and Seychelles–Chagos Thermocline Ridge, whereas between-domain differences were only significant for the north–south gradient (PERMANOVA, α = 0.01). A preliminary test of between-class differences in surface CO2 concentrations from the Orbiting Carbon Observatory-2 demonstrated a small decrease in mean pCO2 with increasing chlorophyll (chl), from 418 to 398 ppm. Simple optical class maps therefore provide an overview of growth conditions, the spatial distribution of resources — from which habitat fragmentation metrics can be calculated, and carbon sequestration potential. Within the 17 year study period, biotic variables were found to have decreased at up to 0.025%a−1 for all optical classes, which is slower than reported elsewhere (Mann-Kendall-Sen regression, α = 0.01). Within the MPA, positive Indian Ocean Dipole conditions and negative Southern Oscillation Indices were weakly associated with decreasing chl, fluorescence line height (FLH), eddy kinetic energy, easterly wind stress and wind stress curl, and with increasing FLH/chl, sea surface temperature, SSH gradients and northerly wind stress, consistent with reduced surface mixing and increased stratification. The optical partitioning scheme described here can be applied in Google Earth Engine to support management decisions at daily or monthly scales, and potential applications are discussed.

Sea-ice loss amplifies summertime decadal CO2 increase in the western Arctic Ocean

Rapid climate warming and sea-ice loss have induced major changes in the sea surface partial pressure of CO2 ($$p_{{\mathrm {CO}}_2}$$). However, the long-term trends in the western Arctic Ocean are unknown. Here we show that in 1994–2017, summer $$p_{{\mathrm {CO}}_2}$$ in the Canada Basin increased at twice the rate of atmospheric increase. Warming and ice loss in the basin have strengthened the $$p_{{\mathrm {CO}}_2}$$ seasonal amplitude, resulting in the rapid decadal increase. Consequently, the summer air–sea CO2 gradient has reduced rapidly, and may become near zero within two decades. In contrast, there was no significant $$p_{{\mathrm {CO}}_2}$$ increase on the Chukchi Shelf, where strong and increasing biological uptake has held $$p_{{\mathrm {CO}}_2}$$ low, and thus the CO2 sink has increased and may increase further due to the atmospheric CO2 increase. Our findings elucidate the contrasting physical and biological drivers controlling sea surface $$p_{{\mathrm {CO}}_2}$$ variations and trends in response to climate change in the Arctic Ocean. Surface CO2 concentrations in the western Arctic Ocean differ due to local processes. During the period 1994–2017, the Canada Basin has shown rapid increases as warming and ice loss enhance air–sea exchange of CO2, whereas the Chukchi Shelf has strong biological activity, resulting in a CO2 sink.

Carbon Dioxide Fluxes to the Atmosphere From Waters Within Flooded Forests in the Amazon Basin

AbstractInundated tropical forests are underrepresented in analyses of the global carbon cycle and constitute 80% of the surface area of aquatic environments in the lowland Amazon basin. Diel variations in CO2 concentrations and exchanges with the atmosphere were investigated from August 2014 to September 2016 in two flooded forests sites with different wind exposure within the central Amazon floodplain (3°23′S, 60°18′W). CO2 profiles and estimates of air–water gas exchange were combined with ancillary environmental measurements. Surface CO2 concentrations ranged from 19 to 329 μM, CO2 fluxes ranged from −0.8 to 55 mmol m−2 hr−1 and gas transfer velocities ranged from 0.2 to 17 cm hr−1. CO2 concentrations and fluxes were highest during the high water period. CO2 fluxes were three times higher at a site with more wind exposure (WE) compared to one with less exposure (WP). Emissions were higher at the WP site during the day, whereas they were higher at night at the WE site due to vertical mixing. CO2 concentrations and fluxes were lower at the W P site following an extended period of exceptionally low water. The CO2 flux from the water in the flooded forest was about half of the net primary production of the forest estimated from the literature. Mean daily fluxes measured in our study (182 ± 247 mmol m−2d−1) are higher than or similar to the few other measurements in waters within tropical and subtropical flooded forests and highlight the importance of flooded forests in carbon budgets.

Carbon Monoxide Variations in the Antarctic Atmosphere from Ground-Based and Satellite Measurement Data

The results of systematic (2003–2017) measurements of the total content and height-averaged relative volume concentration of CO at st. Novolazarevskaya with a spectrometer with a resolution of 0.2 cm–1 are presented. The inverse problem of determining the total content of CO as well as interfering gases (H2O and N2O) was solved using the SFIT4 software package. A data analysis indicated that during the measurements the average total CO content at st. Novolazarevskaya was (8 ± 2) 1017 molecules/cm2 and the height-averaged volume concentration was (37 ± 8) ppb. The resulting data were compared with variations in the total CO content at st. Arrival-Heights, MOPITT satellite data, and CO surface concentrations at st. Syowa. The maximum and minimum values of CO were observed in September and January–February, respectively. For all the data series considered, the trends are insignificant; in this case, an increased CO content was observed in 2010, and an increasing trend of the minimum values of CO was observed in recent years (2014–2017). Both stations (Novolazarevskaya and Arrival-Heights) are characterized by an excess of satellite data over ground-based measurement data (19% and 14%, respectively); here, a seasonal dependence of the deviation was observed with minimal deviations in December–January. Data of surface measurements of the total content at st. Novolazarevskaya and Arrival-Heights are rather well consistent, and the average deviation since 2010 was 2.4%. The average concentration of CO at st. Syowa (51 ppb) is higher than the height-averaged concentration at st. Novolazarevskaya. According to spectral, wavelet, and composite analyzes, all data series considered include oscillations in the range of 6–45 months with almost identical periods and phase relationships.

Sensitivity of the simulated CO2 concentration to inter-annual variations of its sources and sinks over East Asia

The study on how the variations in CO2 sources and sinks can affect the CO2 concentration over East Asia would be useful to provide information for policymaker concerning carbon emission reduction. In this study, a nested-grid version of global chemical transport model (GEOS-Chem) is employed to assess the impacts of variations in meteorological parameters, terrestrial fluxes, fossil fuel emissions, and biomass burning on inter-annual variations of CO2 concentrations over East Asia in 2004–2012. Simulated CO2 concentrations are compared with observations at 14 surface stations from the World Data Centre for Greenhouse Gases (WDCGG) and satellite-derived CO2 column density (XCO2) from the Gases Observing SATellite (GOSAT). The comparison shows that the simulated CO2 column density is generally higher than that of GOSAT by 1.33 × 10−6 (annual mean point by point biases averaged over East Asia). The model reasonably captures the temporal variations of CO2 concentrations observed at the ground-based stations, but it is likely to underestimate the peaks-to-troughs amplitude of the seasonal cycle by 50% or more. The simulated surface CO2 concentration in East Asia exhibits the largest inter-annual variation in December-January–February (DJF). The regional mean absolute deviation (MAD) values over East Asia are within (4.4–5.0) × 10−6 for all seasons. Model sensitivity simulations indicate that the inter-annual variations of surface CO2 concentrations are mainly driven by variations of meteorological parameters, and partly modulated by the inter-annual variations of terrestrial fluxes and fossil fuel emissions in local regions. The variations of the terrestrial fluxes and fossil fuel emissions may account for ∼28% of the inter-annual variation of surface CO2 concentration in southern China. The inter-annual variations of the peaks-to-troughs amplitude are dependent on variations of meteorological parameters, terrestrial fluxes and fossil fuel emissions in local regions. The influence of biomass burning emissions is relatively weak.

Correlation between the surface chemistry, the surface free energy and the adhesion of metallic coatings onto plasma-treated Poly(ether ether ketone)

The effects of the surface modification of poly(ether ether ketone) (PEEK) by plasma treatment have been characterized by X-ray Photoelectron Spectroscopy and wettability measurement, while the adhesion of metallic thin films grown by PVD has been assessed by the pull-off test. To investigate the role of the modified surface chemistry on the practical adhesion stress of aluminium thin films, two different plasma technologies were considered: (i) atmospheric pressure plasma and (ii) low pressure microwave plasma. Though on different scales, both of these plasmas under oxidative conditions induced a significant increase of the surface concentration of CO (ketones) and COO (esters and acidic) functional groups, while COC (ether) groups remained constant. It is shown that after plasma functionalization, when the surface concentration of CO and COO are above a critical value, a strong correlation appears between the concentration of these polar groups, the wettability and the adhesion potential.

Spatio-temporal variability of CO over the Eastern Indo-Gangetic Plain (IGP) and in parts of South-East Asia: a MERRA-2-based study

The present study revolves around the distribution of surface CO concentrations around the industrial belts of the Eastern Indo-Gangetic Plains (IGP) and in parts of Southeast Asia over a period of 10 years from January 2007 to December 2016. MERRA-2 reanalysis fields are analysed to study the long-term spatial and seasonal behaviour of CO. The focus is on three CO hotspot areas in this region, denoted by A, B and C, which are further subdivided into eight smaller divisions based on topographical and regional characteristics as discussed in details in “Study Region & Meteorology” section. The monthly average distribution of CO in all the eight zones ranges from 750 (C1) to 3781(A2) ppbv. Very high values are consistently observed in the Indo-Gangetic Plains as compared with other regions during the entire period of study. Seasonal variation of surface CO concentration indicates high values in the post-monsoon or winter season. Analysis of spatio-temporal variation alongside emission, chemical production and loss reveals that presence of surface CO is predominantly due to combustion of fossil fuels and burning of organic matters. Fire hotspot data from FIRMS also support these results. Statistical analysis performed using the non-linear regression model further elucidates the sources of CO in the hotspot areas. The coefficient of determination (R2) values between surface CO concentration (response variable) and emission, chemical production and loss (the independent process variables) for all the zones show interesting results. MERRA-2 does not consider any kind of convective transport as influx and outflux of the hypothetical control volume (box) and as such slightly overestimates the net CO concentration as compared with the ground-based measurements under steady-state scenarios.

Tectonic Controls on Near-Surface Variations in CH4 and CO2 Concentrations along the Northwestern Margin of the Ordos Block, China

Tectonic controls on near-surface CH4 and CO2 concentrations were investigated by measuring CH4 and CO2 concentrations at the surface and a height of 1.5 m, in the different tectonic units that comprise the northwestern margin of Ordos Block, China, which has a complex tectonic structure and a history of strong earthquakes. CH4 and CO2 concentrations varied from 1905 to 2472 ppb and 397.5 to 458.5 ppm, respectively. Surface CH4 and CO2 concentrations were generally higher than those measured at 1.5 m, but showed similar trends, indicating that the measured CH4 and CO2 predominantly originated from underground gases. The CH4 and CO2 concentrations increased with an increasing strike-slip rate across the faults, and concentrations in the blocks with high internal deformation were much higher than those measured in the stable blocks. Regions of extensional deformation had higher gas concentrations than regions that had experienced compressional deformation. The spatial distribution of CH4 and CO2 at the study site had similar trends to faults associated with the Yinchuan Graben. The results of this study indicated that gas source, gas migration pathway, and tectonic stress were the main factors that influenced gas emission. The key factor is tectonic stress, which controlled the formation of tectonic structures, changed the pathway of degassing, and acted as the driving force for gas migration. The results of this study clarify the mechanism of CH4 and CO2 degassing in faulted regions and suggest that CH4 and CO2 concentrations may be useful precursors in the monitoring of seismic activity. The results may also help inform future assessments of the contribution of geological sources to greenhouse gas emissions.

Sources and variability of CO2 in a prealpine stream gravel bar

AbstractGravel bars (GBs) contribute to carbon dioxide (CO2) emissions from stream corridors, with CO2 concentrations and emissions dependent on prevailing hydraulic, biochemical, and physicochemical conditions. We investigated CO2 concentrations and fluxes across a GB in a prealpine stream over three different discharge‐temperature conditions. By combining field data with a reactive transport groundwater model, we were able to differentiate the most relevant hydrological and biogeochemical processes contributing to CO2 dynamics. GB CO2 concentrations showed significant spatial and temporal variability and were highest under the lowest flow and highest temperature conditions. Further, observed GB surface CO2 evasion fluxes, measured CO2 concentrations, and modelled aerobic respiration were highest at the tail of the GB over all conditions. Modelled CO2 transport via streamwater downwelling contributed the largest fraction of the measured GB CO2 concentrations (31% to 48%). This contribution increased its relative share at higher discharges as a result of a decrease in other sources. Also, it decreased from the GB head to tail across all discharge‐temperature conditions. Aerobic respiration accounted for 17% to 36% of measured surface CO2 concentrations. Zoobenthic respiration was estimated to contribute between 4% and 8%, and direct groundwater CO2 inputs 1% to 23%. Unexplained residuals accounted for 6% to 37% of the observed CO2 concentrations at the GB surface. Overall, we highlight the dynamic role of subsurface aerobic respiration as a driver of spatial and temporal variability of CO2 concentrations and evasion fluxes from a GB. As hydrological regimes in prealpine streams are predicted to change following climatic change, we propose that warming temperatures combined with extended periods of low flow will lead to increased CO2 release via enhanced aerobic respiration in newly exposed GBs in prealpine stream corridors.