Scavenging Processes Research Articles

Subarctic Pacific Intermediate Water: An Oceanic Highway for the Transport of Trace Metals in the North Pacific

AbstractGEOTRACES is an international collaboration project aiming to unravel the distributions of trace elements and their isotopes in the global ocean. As part of the GEOTRACES‐Japan project, we carried out two surveys in the subarctic Pacific in 2012 and 2017. Here, we synthesize the outcomes of research completed so far associated with these surveys. Together our findings revealed that the Subarctic Pacific Intermediate Water is an efficient carrier of trace metals. Trace metals such as iron and manganese originating in coastal regions are transported far into the open ocean due to combinations of favorable conditions. First, the young upper Subarctic Pacific Intermediate Water receives fresh inputs of trace metals, which are stabilized by organic ligands, from terrestrial sources. Meanwhile, the lower Subarctic Pacific Intermediate Water has a relatively low dissolved oxygen concentration, which slows down scavenging processes and allows trace metals to persist in seawater. Decaying sinking organic matter also releases additional trace metals into the intermediate water. The Subarctic Pacific Intermediate Water has unusually high concentrations of dissolved zinc relative to silicate, even though zinc and silicate generally have strongly coupled distribution patterns in the global ocean. We hope that the datasets and insights generated by our surveys and associated studies can contribute to greater understanding of the subarctic Pacific and provide useful information for future studies.

Highly Active Ice-Nucleating Particles at the Summer North Pole.

The amount of ice versus supercooled water in clouds is important for their radiative properties and role in climate feedbacks. Hence, knowledge of the concentration of ice‐nucleating particles (INPs) is needed. Generally, the concentrations of INPs are found to be very low in remote marine locations allowing cloud water to persist in a supercooled state. We had expected the concentrations of INPs at the North Pole to be very low given the distance from open ocean and terrestrial sources coupled with effective wet scavenging processes. Here we show that during summer 2018 (August and September) high concentrations of biological INPs (active at >−20°C) were sporadically present at the North Pole. In fact, INP concentrations were sometimes as high as those recorded at mid‐latitude locations strongly impacted by highly active biological INPs, in strong contrast to the Southern Ocean. Furthermore, using a balloon borne sampler we demonstrated that INP concentrations were often different at the surface versus higher in the boundary layer where clouds form. Back trajectory analysis suggests strong sources of INPs near the Russian coast, possibly associated with wind‐driven sea spray production, whereas the pack ice, open leads, and the marginal ice zone were not sources of highly active INPs. These findings suggest that primary ice production, and therefore Arctic climate, is sensitive to transport from locations such as the Russian coast that are already experiencing marked climate change.

Challenge of modelling GLORIA observations of upper troposphere–lowermost stratosphere trace gas and cloud distributions at high latitudes: a case study with state-of-the-art models

Abstract. Water vapour and ozone are important for the thermal and radiative balance of the upper troposphere (UT) and lowermost stratosphere (LMS). Both species are modulated by transport processes. Chemical and microphysical processes affect them differently. Thus, representing the different processes and their interactions is a challenging task for dynamical cores, chemical modules and microphysical parameterisations of state-of-the-art atmospheric model components. To test and improve the models, high-resolution measurements of the UT–LMS are required. Here, we use measurements taken in a flight of the GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) instrument on HALO (High Altitude and LOng Range Research Aircraft). The German research aircraft HALO performed a research flight on 26 February 2016 that covered deeply subsided air masses of the aged 2015/16 Arctic vortex, high-latitude LMS air masses, a highly textured region affected by troposphere-to-stratosphere exchange and high-altitude cirrus clouds. Therefore, it provides a challenging multifaceted case study for comparing GLORIA observations with state-of-the-art atmospheric model simulations in a complex UT–LMS region at a late stage of the Arctic winter 2015/16. Using GLORIA observations in this manifold scenario, we test the ability of the numerical weather prediction (NWP) model ICON (ICOsahedral Nonhydrostatic) with the extension ART (Aerosols and Reactive Trace gases) and the chemistry–climate model (CCM) EMAC (ECHAM5/MESSy Atmospheric Chemistry – fifth-generation European Centre Hamburg general circulation model/Modular Earth Submodel System) to model the UT–LMS composition of water vapour (H2O), ozone (O3), nitric acid (HNO3) and clouds. Within the scales resolved by the respective model, we find good overall agreement of both models with GLORIA. The applied high-resolution ICON-ART set-up involving an R2B7 nest (local grid refinement with a horizontal resolution of about 20 km), covering the HALO flight region, reproduces mesoscale dynamical structures well. Narrow moist filaments in the LMS observed by GLORIA at tropopause gradients in the context of a Rossby wave breaking event and in the vicinity of an occluded Icelandic low are clearly reproduced by the model. Using ICON-ART, we show that a larger filament in the west was transported horizontally into the Arctic LMS in connection with a jet stream split associated with poleward breaking of a cyclonically sheared Rossby wave. Further weaker filaments are associated with an older tropopause fold in the east. Given the lower resolution (T106) of the nudged simulation of the EMAC model, we find that this model also reproduces these features well. Overall, trace gas mixing ratios simulated by both models are in a realistic range, and major cloud systems observed by GLORIA are mostly reproduced. However, we find both models to be affected by a well-known systematic moist bias in the LMS. Further biases are diagnosed in the ICON-ART O3, EMAC H2O and EMAC HNO3 distributions. Finally, we use sensitivity simulations to investigate (i) short-term cirrus cloud impacts on the H2O distribution (ICON-ART), (ii) the overall impact of polar winter chemistry and microphysical processing on O3 and HNO3 (ICON-ART and EMAC), (iii) the impact of the model resolution on simulated parameters (EMAC), and (iv) consequences of scavenging processes by cloud particles (EMAC). We find that changing the horizontal model resolution results in notable systematic changes for all species in the LMS, while scavenging processes play a role only in the case of HNO3. We discuss the model biases and deficits found in this case study that potentially affect forecasts and projections (adversely) and provide suggestions for further model improvements.

Black carbon over a high altitude Central Himalayan Glacier: Variability, transport, and radiative impacts.

Ambient equivalent black carbon (BC) measurements spanning from June to October have been carried out over an adjoining location of Satopanth and Bhagirath-Kharak Glaciers (3858m, amsl) of Central Himalaya during the year 2019. Hourly BC varied from 12ngm-3 to 439ngm-3 during the entire period of observation. Monthly averaged BC values showed the highest concentration during June (230.96±85.46ngm-3) and the lowest in August (118.02±71.63ngm-3). The decrease in BC during monsoon months is attributed to limited long-range transport and rapid wet scavenging processes. Transport model studies indicate a higher retention time of tracer in Uttarakhand, Punjab, Haryana, and adjacent polluted valley regions with increased biomass burning (BB) incidences. The high rate of BC influx during June, September, and October was attributed to transport from the polluted Indo-Gangetic Plain (IGP) region, wildfires, and vehicular emissions in the valley region. Higher equivalent brown carbon (BrC) influx is linked to BB, especially wood-burning, during intense forest fires at slopes of mountains. Data obtained from limited BC observations during the 2011-19 period showed no significant BC influx change during post-monsoon. The strong correlation between BC mass and BB affirms the dominant role of BB in contributing BC to the Glacier region. Increased TOA forcing induced by surface darkening and BC atmospheric radiative heating indicate an additional warming and possible changes of the natural snow cycle over the glacier depending on the characteristics and extent of debris cover.

PtaERF194 inhibits plant growth and enhances drought tolerance in poplar.

The water deficits limit the growth and development of agricultural and forest organisms. The AP2/ethylene response factor (ERF) family has been identified as one of the largest plant-specific transcription factors (TFs) essential for plant development and stress response. The function of PtaERF194 in growth and drought tolerance was detected in the overexpression (OX) and RNA interference (RNAi) transgenic poplar 717 hybrids (Populus tremula × Populus alba). Plant growth, stem vessels, water-use efficiency (WUE), chlorophyll content and PtaERF194 co-expressed genes were analyzed using morphological, physiological and molecular methods. Overexpression seedlings showed a shorter and smaller phenotype along with smaller and more vessels compared with the wild-type (WT). Physiological indices indicated that OX with low transpiration and stomatal conductance improved the tolerance to drought by enhancing WUE, limiting water loss and maintaining high water potential. A total of 12 differentially expressed genes co-expressed with PtaERF194 were identified, and they worked together to regulate drought tolerance through the abscisic acid signaling and reactive oxygen species scavenging processes. However, RNAi plants showed similar morphology and physiology to WT, suggesting that the function of PtaERF194 was redundant with other ERF TFs. The findings of the current study may shed new light on the positive function of ERF TFs in plant drought stress tolerance.

Functional differences in scavenger communities and the speed of carcass decomposition.

Carcass decomposition largely depends on vertebrate scavengers. However, how behavioral differences between vertebrate scavenger species, the dominance of certain species, and the diversity of the vertebrate scavenger community affect the speed of carcass decomposition is poorly understood. As scavenging is an overlooked trophic interaction, studying the different functional roles of vertebrate species in the scavenging process increases our understanding about the effect of the vertebrate scavenger community on carcass decomposition. We used motion‐triggered infrared camera trap footages to profile the behavior and activity of vertebrate scavengers visiting carcasses in Dutch nature areas. We grouped vertebrate scavengers with similar functional roles. We found a clear distinction between occasional scavengers and more specialized scavengers, and we found wild boar (Sus scrofa) to be the dominant scavenger species in our study system. We showed that these groups are functionally different within the scavenger community. We found that overall vertebrate scavenger diversity was positively correlated with carcass decomposition speed. With these findings, our study contributes to the understanding about the different functional roles scavengers can have in ecological communities.

Detecting the Causal Nexus between Particulate Matter (PM10) and Rainfall in the Caribbean Area

In this study, we investigate the interactions between particulate matter that have an aerodynamic diameter less than 10 μm diameter (PM10) and rainfall (RR) in entropy framework. Our results showed there is a bidirectional causality between PM10 concentrations and RR values. This means that PM10 concentrations influence RR values while RR induces the wet scavenging process. Rainfall seasonality has a significant impact on the wet scavenging process while African dust seasonality strongly influence RR behavior. Indeed, the wet scavenging process is 5 times higher during the wet season while PM10 impact on RR is 2.5 times higher during the first part of the high dust season. These results revealed two types of causality: a direct causality (RR to PM10) and an indirect causality (PM10 to RR). All these elements showed that entropy is an efficient way to quantify the behavior of atmospheric processes using ground-based measurements.

Comparing scavenging in marine and terrestrial ecosystems: a case study with fish and gull carcasses in a small Mediterranean island

Carrion consumption by scavengers is a key component of both terrestrial and aquatic food webs. However, there are few direct comparisons of the structure and functioning of scavenging communities in different ecosystems. Here, we monitored the consumption of 23 fish (seabream Sparus aurata) and 34 bird (yellow-legged gull Larus michahellis) carcasses on a small Mediterranean island (Isla Grosa, southeastern Spain) and surrounding waters in summer to compare the structure of the scavenger assemblages and their carrion consumption efficiencies in terrestrial and shallow water habitats. Scavenging was highly efficient both in marine and terrestrial environments, especially in the presence of a highly abundant vertebrate scavenger species, the yellow-legged gull. The vertebrate scavenger community was richer in the marine environment, whereas the invertebrate community was richer on land. The scavenger network was usually well-structured (i.e., nested), with the exception of the community associated with fish terrestrial carcasses, which were almost monopolized by yellow-legged gulls. In contrast, gulls left conspecific carcasses untouched, thus allowing longer persistence of gull carcasses on land and their exploitation by a diverse insect community. Our study shows important differences in the scavenging process associated with environment and carcass type. Promising avenues for further eco-evolutionary and applied research arise from the comparison of scavenging processes in terrestrial and marine ecosystems, from small islands to continents.

CFD Analysis of a Large Marine Engine Scavenging Process

The scavenging process is an important part of the two-stroke engine operation. Its efficiency affects the global engine performance such as power, fuel consumption, and pollutant emissions. Slow speed marine diesel engines are uniflow scavenged, which implies inlet scavenging ports on the bottom of the liner and an exhaust valve on the top of the cylinder. A CFD model of such an engine process was developed with the OpenFOAM software tools. A 12-degree sector of the mesh was used corresponding to one of the 30 scavenging ports. A mesh sensitivity test was performed, and the cylinder pressure was compared to experimental data for the analyzed part of the process. The scavenging performances were analyzed for real operation parameters. The influence of the scavenge air pressure and inlet ports geometric orientation was analyzed. The scavenging process is analyzed by means of a passive scalar representing fresh air in the cylinder. Isosurfaces that show the concentration of fresh air were presented. The variation of oxygen and carbon dioxide with time and the axial and angular momentum in the cylinder were calculated. Finally, the scavenging performance for the various operation parameters was evaluated by means of scavenging efficiency, charging efficiency, trapping efficiency, and delivery ratio. It was found that the scavenging efficiency decreases with the engine load due to the shorter time for the process. The scavenging efficiency increases with the pressure difference between the exhaust and scavenging port, and the scavenging efficiency decreases with the increase in the angle of the scavenging ports. It was concluded that smaller angles than the industry standard of 20° could be beneficial to the scavenging efficiency. In the investigation, the charging efficiency ranged from 0.91 to over 0.99, the trapping efficiency ranged from 0.54 to 0.83, the charging efficiency ranged from 0.78 to 0.92, and the delivery ratio ranged from 1.21 to 2.03.

Comparison of an opposed-piston free-piston engine using single and dual channel uniflow scavenging

• The OP2S-FPE using single-channel and dual-channel uniflow scavenging was proposed. • The CFD model of the engine was built, and simulation parameters were discussed. • The single-channel engine has advantages of fast heat release rate and low emission. • Energy loss comparisons between the single and dual channel engine was presented. • The single-channel uniflow scavenging combustor is suitable for the engine. The free-piston engine is an unconventional engine characterized by a free-moving piston without a crankshaft system. The scavenging process recharges the engine and is crucial to mixture formation and stable combustion. In this paper, a single-channel structure for a two-stroke opposed-piston free-piston engine was proposed. A comparative study of spray, combustion, emissions and energy balance was presented using computational fluid dynamics simulations. Grid independence and step sensitivity were discussed in order to improve the simulation accuracy. The results show that the combustion efficiency of the engine with single-channel structure increased to 98.1%, and the combustion duration decreased by 59.8%. Due to the successful combustion organization, the single-channel engine achieves low emissions even if the CO2 content is slightly higher. The thermodynamic analysis of the engine reveals that the energy loss from scavenging process contributes the largest part to the total energy loss. In addition, the study initially reveals the performance stability of the single-channel engine under different combustion conditions.

Mean value first principle engine model for predicting dynamic behaviour of two-stroke marine diesel engine in various ship propulsion operations

Analysis of ship propulsion system performance is often performed using detailed hydrodynamic models to assess load changes, which are subsequently compared to static engine limits, or by detailed engine models that are rarely integrated with sufficiently detailed propulsion models for load change estimation. To investigate the dynamic engine (overloading) behaviour and ship propulsion performance under various heavy operating conditions, a Mean Value First Principle Parametric (MVFPP) engine model is integrated into a ship propulsion system model in this paper. An upgraded thermodynamic-based MVFPP model for two-stroke marine diesel engines is presented, in particular a newly developed MVFPP gas exchange model. Based on the integrated propulsion system model of a benchmark ocean-going chemical tanker, the engine dynamic behaviour during ship acceleration, deceleration and crash stop has been investigated. Results show that, during dynamic processes, the engine could be thermally overloaded even if the engine power trajectory is inside the static engine operating envelope. The paper contributes to finding proper indicators for thermal overloading of modern two-stroke marine diesel engines. It is demonstrated that when matching the engine with the propeller and designing the ship propulsion control system, not only the static engine operating envelope, but also the dynamic engine behaviour should be considered. • Mean Value First Principle Parametric (MVFPP) model for 2-stroke marine diesel engine. • Novel approach to two-zone modelling of scavenging process. • MVFPP model is balanced choice to predict engine behavior in drive system simulation. • Static performance maps & limits inadequate for prediction of engine dynamic behavior. • MVFPP model can provide deeper understanding of thermal overloading of engines.

Trace elements (Fe, Mn, Co, Cu, Cd, and Ni) in the East Sea (Japan Sea): Distributions, boundary inputs, and scavenging processes

The distributions of trace elements (Fe, Mn, Co, Cu, Cd, and Ni) were measured, for the first time, in the entire East Sea (22 stations, n = 276, 0–3400 m), which is located in the region directly affected by East Asian monsoon and the downstream of Tsushima Current. In general, the distribution patterns of these trace elements were similar to those in the major oceans. However, relatively higher concentrations of trace elements, except for Ni, were observed in the surface layer due to the pronounced external inputs (atmospheric deposition and/or continental shelf input). In addition, we observed unusually high concentrations of Fe and Mn in the bottom layer of the Ulleung Basin, owing to large benthic inputs. These inputs seem to be associated with the significant production/dissolution of Fe and Mn in organic-rich sediments (> 2.5%) and the subsequent diffusion of dissolved organic matter (DOM)-complexed Fe and Mn into the overlying seawater. In this bottom layer, the concentrations of Fe and Mn approached 13 and 57 nmol kg−1, respectively, which are an order of magnitude higher than those in the oxic deep water of other major oceans. Based on the plots of trace elements against nutrients, the scavenging of Co in the deep East Sea is found to be particularly efficient relative to other major oceans. The concentrations of Co in the deep East Sea (2500–3400 m) are the lowest reported concentrations (2–8 pmol kg−1) compared with those from the same depths in the global oceans, while those in the surface layer are 2- and 5-fold higher than those in the North Pacific and North Atlantic Oceans, respectively. Thus, the distinct distribution patterns of trace elements in this sea reveal the efficient scavenging processes related to the high sinking fluxes of particles under the significant boundary input conditions (atmospheric deposition, continental shelf input, and benthic input).

A Regulatory Network of Heat Shock Modules-Photosynthesis-Redox Systems in Response to Cold Stress Across a Latitudinal Gradient in Bermudagrass.

Bermudagrass (Cynodon dactylon Pers.) is a wild Poaceae turfgrass with various genotypes and phenotypes. In this study, 16 wild bermudagrass germplasms were collected from 16 different sites along latitudinal gradients, and different temperature treatments were compiled and used for physiological and transcriptome analysis. To explore the correlation between the key differentially expressed genes and physiological indicators, a total of 14,654 DEGs were integrated from the comparison of different temperature treatments and used for weighted gene co-expression network analysis. Through comparative transcriptome analysis and gene annotation, the results showed that differential gene expression profiles in networks are associated with the plant growth, photosystem, redox system, and transcriptional regulation to cold stress in bermudagrass. In particular, genes encoding HSP70/90 and HsfA3/A8 are not only regulated by temperature stress, but also directly or indirectly interplay with the processes of peroxide scavenging and chlorophyll synthesis under cold stress. Besides, through a weight evaluation analysis of various physiological indexes, we identified an accession of wild bermudagrass with relatively strong cold resistance. These results provide important clues and resources to further study the responses to low-temperature stress in bermudagrass.

Assessment of Waste Scavenging Activities in Calabar, Cross River State, Nigeria

The study was focus on assessing waste scavenging activities in Calabar, Cross River State. Specifically, the study appraised the socioeconomic characteristics of solid waste scavengers in Calabar and analysed the contributions of scavengers in the waste management process. The study obtained data through questionnaire administration. A total of 50 copies of questionnaire were distributed purposively to waste scavengers in the study area while descriptive statistics was used in carrying out analysis. It was observed that scavenging is exclusively carried out by males and those between 31 years and 40 years dominate the waste scavenging process. It was equally revealed that the married form a larger percent of scavengers in the study area. Scavengers were observed to be engaged in picking up irons/metals, plastics, glasses, copper, bottles as well as vegetables and food remains. Scavengers are mainly involved in the exercise in order to enable them earn a living. Therefore, wastes materials that are pickup in the process are sold out to recycling companies. Specifically, iron scraps pickers sell them to iron recycling companies while vegetable waste pickers sell to fertilizer production companies. Very few scavengers use the wastes they pick up for personal uses. However, it was noted that scavengers contribute positively in the management of solid waste in Calabar. Based on the findings, it was suggested that waste sorting should be encouraged among youths through the organization of sensitization campaigns and the awareness since it has the potentials of reducing unemployment while promoting waste management. Equally, scavengers should be recognized by the government as managers in the waste sector and be given some incentives

Improving the antioxidant activity of natural antioxidant honokiol by introducing the amino group.

Exploring and synthesizing the compounds with stronger antioxidant activity have always been the goal of researchers. Herein, the substitution effects of the amino (NH2-) group with the excellent electron-donating ability in different positions on the antioxidant activity of Honokiol (Hon) were systematically explored by using the quantum chemistry calculation based on the density functional theory method. The three possible antioxidant mechanisms of Hon and its four NH2-substituted derivatives (Hon1-Hon4), containing the hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were explored in depth considering the gas and solvent phases. In addition, the frontier molecular orbital energies, natural bond orbital (NBO) charge population, and global descriptive parameters were used to study their antioxidant activity. The results indicate that compared with the original molecule Hon, the NH2 substituents would have the stronger antioxidant activity. Moreover, the radical scavenging process of Hon and its derivatives has a disposition to the HAT and SPLET mechanisms in the gas and solvent phases, respectively. Meaningfully, owing to the lowest bond dissociation enthalpy and proton affinity values, Hon4 would show the most prominent antioxidant activity by comparison with the other compounds. In conclusion, this work will provide the purposeful reference for designing and synthesizing the antioxidants with more outstanding performance.

A Comprehensive Numerical Analysis of the Scavenging Process in a Uniflow Two-Stroke Diesel Engine for General Aviation

The scavenging process of two-stroke engines plays a fundamental role in cylinder flow patterns and in the overall engine performance. In this work, 3D CFD simulations of the scavenging in a uniflow, two-stroke, compression ignition engine for general aviation, named GF56, have been performed by using a 3D finite-volume FANS equations solver with k-ϵ closure. The GF56 engine consists of six cylinders, separated into two quasi-symmetric banks. Both the right and the left banks, together with the corresponding cylinders, are carefully analyzed. Charging and trapping efficiencies are computed as a function of the delivery ratio for different mass flow rates entering into the plenum, and the influence of the exhaust pressure and of the cylinder’s location in the bank are analyzed. The results show that the fresh air trapped during the scavenging process is quite similar for each cylinder of the right bank and it is about 92% of the in-cylinder mass. The cylinder’s location in the bank by itself slightly affects the scavenging performance, whereas the pressure profile at the outlet section has a major role. The design of the intake ports is fundamental for establishing the in-cylinder flow field and a new ports configuration is proposed to enhance the swirl ratio and, consequently, the scavenging performance with high delivery ratios.

210Po/210Pb Disequilibria in the Eastern Tropical North Pacific

The 210Po/210Pb disequilibrium was attempted to reveal the small-scale particle dynamics in the eastern tropical North Pacific. Seawater samples in the full water column were collected from three sites in the Tehuantepec bowl near the East Pacific Ridge for determination of dissolved and particulate 210Po and 210Pb. Our results show that TPo/TPb activity ratios in the full water column at the three sites are less than 1, with an average of 0.56, indicating that the total 210Po in the oligotrophic sea is significantly deficient. The activity ratios of DPo/DPb in the dissolved phase are less than 1, while those in the particulate phase are greater than 1 (except for the bottom 300 m), indicating fractionation between 210Po and 210Pb in the scavenging process. A negative linear relationship between 210Po deficit and silicate proves that biological activities are responsible for 210Po deficiency in the upper 200 m. However, the deficit of 210Po in the bottom 300 m may be caused by the horizontal transport of the hydrothermal plume. After correcting the horizontal contribution, the removal rates of 210Po for the 200–1,500 m and the bottom 300 m layers increased by 7.5–21 and 26.1–29.5%, respectively. Correspondingly, the variation range of the residence time of a total 210Po became smaller. Our calculations suggest that horizontal transport is acting as a stabilizer for small-scale variation in the 210Po deficit in the eastern tropical North Pacific. Our study highlights the need to pay more attention to the small-scale variation of 210Po deficit when applying 210Po/210Pb disequilibria to trace biogeochemical processes, and the mechanism responsible for this variation deserves further study.

Mesoporous silica nanosphere-based oxygen scavengers

We synthesized mesoporous silica nanospheres (MSNs) with small particle size (under 100 nm) and large surface areas (>800 m 2 /g) by modified Stöber method. We investigated coating of oxygen adsorber materials (iron-based and titania-based) by atomic layer deposition on the prepared MSNs. We found that MSNs without any coating are capable of adsorbing oxygen by physisorption, and that due to their high surface areas they can outperform commercial oxygen scavengers for atmospheres with moderate and low humidity levels. Their performance is further enhanced for optimized thickness of FeO x or TiO x coating, where chemisorption contributes to oxygen scavenging process. To further investigate the oxygen adsorption on MSNs, samples with different annealing times were prepared and characterized, and the oxygen adsorption could be attributed to incomplete removal of silicon precursor residue. While the samples with prolonged annealing time do not exhibit oxygen adsorption, the high oxygen adsorption capacity can be restored by glucose treatment which results in carbon-based surface coating of MSNs. Due to their fast response and high oxygen adsorption capacity, the prepared materials are highly promising as oxygen scavengers, in particular for applications in dry environments where humidity activation is undesirable. • Mesoporous silica nanospheres (MSN) exhibit excellent oxygen scavenger performance. • MSN samples with small sizes and high surface areas are prepared by a simple process. • MSNs (5 h annealing) outperform commercial O 2 scavengers in dry air. • The performance is further enhanced by atomic layer deposition coating of FeOx or TiOx. • The most significant performance enhancement is achieved by glucose treatment.

237Np and 241Am as Fingerprints in the Major River Basins of Southern China and North South China Sea: A Land-Sea Perspective.

During the global nuclear weapon tests, large amounts of radioactive elements are released into the environment. Long-period actinide elements such as Np, Pu, and Am exhibit different behaviors in various environments, and their isotope characteristic fingerprints are of great significance for studying the distribution, migration, and prediction of radioactive pollutants. To investigate the distribution of 241Am and 237Np in southern China, activities of 241Am (0.008 ± 0.012–0.932 ± 0.066 Bq/kg) and 237Np (0.037 ± 0.003–1.458 ± 0.063 mBq/kg), 237Np/239Pu atom ratios (0.055 ± 0.003–0.864 ± 0.054), and 241Am/239+240Pu activity ratios (0.033 ± 0.075–15.870 ± 0.477) in 95 surface sediment samples collected from the northern South China Sea and major river basins were analyzed for the first time. Due to the different scavenging mechanisms of Am and Pu, 241Am is preferentially concentrated by sinking the particulate, while plutonium is scavenged in the coastal area, resulting in a higher 241Am/239+240Pu activity ratio in estuary and coastal areas. The distribution of 237Np shows obvious spatial inhomogeneity as the high migration rate. The relevant fingerprint characteristic has changed greatly and needs to be updated urgently. As a result of the convergence of land and sea, 241Am, 239,240Pu, and 237Np are dominated by terrestrial sediments and deposited in the coastal area of southern China, which should be paid more attention to. This work can establish China’s current neptunium radioactivity database, and the difference in Np, Pu, and Am scavenging processes may be a powerful tool for evaluating the impact of the Pearl River Estuary salt tide.

Coupled modeling of in- and below-cloud wet deposition for atmospheric 137Cs transport following the Fukushima Daiichi accident using WRF-Chem: A self-consistent evaluation of 25 scheme combinations

Wet deposition, including both in- and below-cloud scavenging, is critical for the atmospheric transport modeling of 137Cs following the Fukushima Daiichi Nuclear power plant (FDNPP) accident. Although intensively investigated, wet deposition simulation is still subject to uncertainties of meteorological inputs and wet scavenging modeling, leading to biased 137Cs transport prediction. To reduce the dual uncertainties, in- and below-cloud wet scavenging schemes of 137Cs were simultaneously integrated into Weather Research and Forecasting-Chemistry (WRF-Chem), yielding online coupled modeling of meteorology and the two wet scavenging processes. The integration was performed using 25 combinations of different in- and below-cloud schemes, covering most schemes in the literature. Two microphysics schemes were also tested to better reproduce the precipitation. The 25 models and the ensemble mean of 9 representative models were systematically compared with the below-cloud-only WRF-Chem model, using the cumulative deposition and atmospheric concentrations of 137Cs measurements. The results reveal that, with the Morrison's double moment cloud microphysics scheme, the developed models could better reproduce the rainfall and substantially improve the cumulative deposition simulation. The in-cloud scheme is influential to the model behaviors and those schemes considering cloud parameters also improve the atmospheric concentration simulations, whereas the others solely dependent on the rain intensity are sensitive to meteorology. The ensemble mean achieves satisfactory performance except one plume event, but still outperforms most models.