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Solving the challenges faced during the measurement of the cross-interface transfer of perfluoroalkyl acids (PFAAs) in lakes is crucial for clarifying environmental behaviours of these chemicals and their efficient governance. This study developed a multimedia fugacity model based on the quantitative water-air-sediment interaction (QWASI) covering abiotic/biotic matrices to investigate the cross-interface transfer and fate of PFAAs in Luoma Lake, a typical PFAA-contaminated shallow lake in eastern China. The accuracy and reliability of the established model were confirmed using Percent bias and Monte Carlo simulation, respectively. Using the QWASI model, the multimedia transfer of the PFAAs and their accumulation and persistence in different sub-compartments were described and measured, and the differences among individual PFAAs were explored. The simulation results showed that the sedimentation and resuspension of PFAAs were the most intense cross-interfacial transfers, and the sediments served as a chemical sink in the long term. A significant negative correlation of N C-F (the number of CF bonds) with the relative outflow flux (T W · out-ct ) but a positive correlation with the relative net transfer across the interface between water and aquatic plants (T p-ct ) was detected, indicating that the PFAA migration capacity decreased but the bioaccumulation potential increased with the CF bond number. The persistence in water (P w ) of individual PFAAs ranged from 19.65d (PFOA) to 32.22d (PFOS), with an average of 26.15d; their persistence in sediment (P s ) ranged from 432d (PFBA) to 3216d (PFOS), with an average of 1524d, increasing linearly with an increase in N C-F . The water advection flows into and out of the lake (Q W · in and Q W · out ), the PFAA concentration of water inflow (C W · in ), and bioconcentration factor of aquatic plants (BCF p ) were the primary parameters sensitive to PFAAs in all sub-compartments, which are essential indexes for exploring promising remediation pathways for lacustrine PFAA contamination based on the fugacity model simulation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Ground ozone (O 3 ) pollution has emerged as a prominent environmental concern in eastern cities of China, particularly during the summer and autumn seasons. However, a comprehensive investigation into the three-dimensional (3-D) evolution characteristics of O 3 within complicated urban environments, especially in lake-land environment, is notably scarce. To enhance our understanding of the mechanisms underlying elevated O 3 concentrations within a 3-D scale, this study employed an ozone lidar to delineate vertical ozone profiles in Changzhou, a typical city in China with complicated anthropogenic and biogenic emissions and complex land cover. The process analysis tool integrated into the Weather Research and Forecasting with Chemistry (WRF-Chem) model was further utilized to analyze the formation processes of O 3 . The results unveil a persistent O 3 pollution episode lasting over 15 days in Changzhou during the study period, with multiple peaks exceeding 200 μg m⁻³. Notably, O 3 predominantly accumulated within the boundary layer, confined below 1.2 km. Both ground and vertical contributions to this pollution were mainly due to local chemical reactions, with a maximum near-surface contribution reaching 19 ppb h -1 and a vertical contribution of 10 ppb h -1 at the height of 900 ± 200 m. Furthermore, episodes of the enhanced O 3 concentrations on August 9 and August 26, 2021, were influenced by external advection process. Our study also found that local circulation plays an important role in the accumulation of surface O 3 during certain periods. There was a temperature difference between the surface of Lake Tai and the adjacent land, resulting in the formation of lake-land breezes that facilitate the transport of O 3 from the lake surface to the terrestrial environment during pollution events. Our study emphasizes the necessity of reducing local pollutant emissions and implementing joint emission controls as the primary strategies for mitigating O 3 pollution in Changzhou and the surrounding region., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Soil Cd contamination has become increasingly prominent in karst regions. Studies have generally elucidated the natural sources of Cd in high-background areas and analyzed their migration and enrichment mechanisms. This study comprehensively analyzed the total content and speciation of Cd in high-background areas using the delayed geochemical hazard (DGH) model to identify the sources of Cd in the region. The results indicated that Cd in the research area followed a pattern of gradual geochemical disasters. In Quaternary soil, brick-red soil, and submergenic paddy soil with hydromorphic characteristics, 32%, 7.69%, and 30% of soil Cd samples exceeded the critical threshold of the releasable total amount, respectively. Based on the DGH model, it was concluded that Cd in this region was mainly influenced by human activities. Field investigations corroborated this conclusion and aligned with the findings. Compared with the traditional source apportionment receptor models (mainly PCA and PMF), the DGH model not only saved considerable time and cost, but also avoided uncertainty associated with the results and complex and varied data processing and computational analysis processes. Moreover, the DGH model was able to identify the factors having the greatest impact on the ecological risk of Cd in the research area, thus facilitating targeted prevention and management planning based on the characteristics or chemical properties of their elements., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Thermodynamic modeling is still the most widely used method to characterize aerosol acidity, a critical physicochemical property of atmospheric aerosols. However, it remains unclear whether gas-aerosol partitioning should be incorporated when thermodynamic models are employed to estimate the acidity of coarse particles. In this work, field measurements were conducted at a coastal city in northern China across three seasons, and covered wide ranges of temperature, relative humidity and NH 3 concentrations. We examined the performance of different modes of ISORROPIA-II (a widely used aerosol thermodynamic model) in estimating aerosol acidity of coarse and fine particles. The M0 mode, which incorporates gas-phase data and runs the model in the forward mode, provided reasonable estimation of aerosol acidity for coarse and fine particles. Compared to M0, the M1 mode, which runs the model in the forward mode but does not include gas-phase data, may capture the general trend of aerosol acidity but underestimates pH for both coarse and fine particles; M2, which runs the model in the reverse mode, results in large errors in estimated aerosol pH for both coarse and fine particles and should not be used for aerosol acidity calculations. However, M1 significantly underestimates liquid water contents for both fine and coarse particles, while M2 provides reliable estimation of liquid water contents. In summary, our work highlights the importance of incorporating gas-aerosol partitioning when estimating coarse particle acidity, and thus may help improve our understanding of acidity of coarse particles., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2023. Published by Elsevier B.V.)

Polybromodiphenyl ethers (PBDEs), the widely used flame retardants, are common contaminants in surface soils at e-waste recycling sites. The association of PBDEs with soil colloids has been observed, indicating the potential risk to groundwater due to colloid-facilitated transport. However, the extent to which soil colloids may enhance the spreading of PBDEs in groundwater is largely unknown. Herein, we report the co-transport of decabromodiphenyl ester (BDE-209) and soil colloids in saturated porous media. The colloids released from a soil sample collected at an e-waste recycling site in Tianjin, China, contain high concentration of PBDEs, with BDE-209 being the most abundant conger (320 ± 30 mg/kg). The colloids exhibit relatively high mobility in saturated sand columns, under conditions commonly observed in groundwater environments. Notably, under all the tested conditions (i.e., varying flow velocity, pH, ionic species and ionic strength), the mass of eluted BDE-209 correlates linearly with that of eluted soil colloids, even though the mobility of the colloids varies markedly depending on the specific hydrodynamic and solution chemistry conditions involved. Additionally, the mass of BDE-209 retained in the columns also correlates strongly with the mass of retained colloids. Apparently, the PBDEs remain bound to soil colloids during transport in porous media. Findings in this study indicate that soil colloids may significantly promote the transport of PBDEs in groundwater by serving as an effective carrier. This might be the reason why the highly insoluble and adsorptive PBDEs are found in groundwater at some PBDE-contaminated sites., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

With the increasing severity of arsenic (As) pollution, quantifying the environmental behavior of pollutant based on numerical model has become an important approach to determine the potential impacts and finalize the precise control strategies. Taking the industrial-intensive Jinsha River Basin as typical area, a two-dimensional hydrodynamic water quality model coupled with Soil and Water Assessment Tool (SWAT) model was developed to accurately simulate the watershed-scale distribution and transport of As in the terrestrial and aquatic environment at high spatial and temporal resolution. The effects of hydro-climate change, hydropower station construction and non-point source emissions on As were quantified based on the coupled model. The result indicated that higher As concentration areas mainly centralized in urban districts and concentration slowly decreased from upstream to downstream. Due to the enhanced rainfall, the As concentration was significantly higher during the rainy season than the dry season. Hydro-climate change and the construction of hydropower station not only affected the dissolved As concentration, but also affected the adsorption and desorption of As in sediment. Furthermore, As concentration increased with the input of non-point source pollution, with the maximum increase about 30%, resulting that non-point sources contributed important pollutant impacts to waterways. The coupled model used in pollutant behavior analysis is general with high potential application to predict and mitigate water pollution., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2023. Published by Elsevier B.V.)

Soil dissolved organic matter (SDOM) is an important part of the DOM pool in terrestrial systems, influencing the transport and fate of many pollutants. In this study, SDOMs from different regions across China were compared by a series of spectroscopic methods, including UV-vis spectroscopy, fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy, and the hydrophobicity was quantified by partition coefficients of SDOM in the aqueous two-phase system (K ATPS ). The molecular weight, aromaticity, and hydrophobicity of SDOM from different regions exhibited strong heterogeneity, K ATPS combined with UV-vis and fluorescence indices can be readily used for differentiating heterogeneous SDOM, and SDOMs were compositionally and structurally different from DOMs in aquatic systems based on spectral characterization. Importantly, the two-phase system (TPS) model has only been validated by DOMs in freshwater systems, and good organic carbon‒water partition coefficient (K OC ) predictive power (RMSE = 0.11) could be provided by the TPS model when applied to heterogeneous SDOM without calibration, showing its broad applicability. Our results demonstrate the applicability of the TPS model for predicting the sorption behavior of terrestrial DOM, broadening the application scope of the TPS model and indicating its potential as a routine model for the risk assessment of hydrophobic organic compounds (HOCs) in organic contaminated sites., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Based on observed meteorological elements, photolysis rates (J-values) and pollutant concentrations, an automated J-values predicting system by machine learning (J-ML) has been developed to reproduce and predict the J-values of O 1 D, NO 2 , HONO, H 2 O 2 , HCHO, and NO 3 , which are the crucial values for the prediction of the atmospheric oxidation capacity (AOC) and secondary pollutant concentrations such as ozone (O 3 ), secondary organic aerosols (SOA). The J-ML can self-select the optimal "Model + Hyperparameters" without human interference. The evaluated results showed that the J-ML had a good performance to reproduce the J-values where most of the correlation (R) coefficients exceed 0.93 and the accuracy (P) values are in the range of 0.68-0.83, comparing with the J-values from observations and from the tropospheric ultraviolet and visible (TUV) radiation model in Beijing, Chengdu, Guangzhou and Shanghai, China. The hourly prediction was also well performed with R from 0.78 to 0.81 for next 3-days and from 0.69 to 0.71 for next 7-days, respectively. Compared with O 3 concentrations by using J-values from the TUV model, an emission-driven observation-based model (e-OBM) by using the J-values from the J-ML showed a 4%-12% increase in R and 4%-30% decrease in ME, indicating that the J-ML could be used as an excellent supplement to traditional numerical models. The feature importance analysis concluded that the key influential parameter was the surface solar downwards radiation for all J-values, and the other dominant factors for all J-values were 2-m mean temperature, O 3 , total cloud cover, boundary layer height, relative humidity and surface pressure., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Black carbon (BC) aerosol can lead to adverse health effects and drive climate change; therefore, the characteristic research and identification of BC sources are essential for lowering emissions. In this study, equivalent black carbon (eBC) measurement was performed using a seven-wavelength Aethalometer (AE33) at an urban site in a typical industrial city (Zibo) of Northern China for the first time. The monitoring was performed from February 2021 to January 2022. The mass absorption cross-section (MAC) of AE33 was optimised using the online elemental carbon (EC) data, and eBC was corrected using the MAC. The corrected annual BC concentration was 1.72 ± 1.18 µg/m 3 . The diurnal variation of BC depicted a bimodal distribution. Furthermore, the BC concentration on weekends was 18% lower than on weekdays. The diurnal variation and weekend effect reflect the critical contributions of traffic emission to BC concentration. The source apportionment of BC was calculated by a constraining Aethalometer model, which restricted the Ångström exponent using the online potassium ions. The results revealed that BC was not significantly affected by biomass burning (BC bb ) in Zibo. The relative contribution of BC bb was higher in winter than in other seasons. The daily morning peak of BC was primarily influenced by traffic sources, whereas the contribution of biomass burning increased after 17:00 in the evening peak. Our findings suggest that it is more important to control fossil fuel sources for BC emission reduction in Zibo, while it is necessary to strengthen the control of biomass combustion sources in winter., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

China's lakes are plagued by cadmium (Cd) pollution. Dissolved organic matter (DOM) significantly regulates Cd(II) transport properties at the sediment-water interface. Understanding the effects of different DOM components on the transportation properties of Cd(II) at the sediment-water interface is essential. In this study, typical DOM from different sources was selected to study Cd(II) mobility at the sediment-water interface. Results showed that terrestrial-derived DOM (fulvic acids, FA) and autochthonous-derived DOM (α-amylase, B1) inhibit Cd(II) sequestration by sediments (42.5% and 5.8%, respectively), while anthropogenic-derived DOM (sodium dodecyl benzene sulfonate, SDBS) increased the Cd(II) adsorption capacity by sediments by 2.8%. Fluorescence quenching coupling with parallel factor analysis (EEM-PARAFAC) was used to characterize different DOM components. The results showed that FA contains three kinds of components (C1, C3: protein-like components, C2: humic-like components); SDBS contains two kinds of components (C1, C2: protein-like components); B1 contains three kinds of components (C1, C2: protein-like components, C3: humic-like components).Three complex reaction models were used to characterize the ability of Cd(II) complex with DOM, and it was found that the humic-like component could hardly be complex with Cd(II). Accordingly, humic-like components compete for Cd(II) adsorption sites on the sediment surface and inhibit Cd(II) adsorption from sediments. Fourier transform infrared spectroscopy (FTIR) of the sediment surface before and after Cd(II) addition was analyzed and proved the competitive adsorption theory. This study provides a better understanding of the Cd(II) mobilization behavior at the sediment-water interface and indicates that the input of humic-like DOM will increase the bioavailability of Cd., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Phthalic acid esters (PAEs) are a group of compounds widespread in the environment. To investigate the occurrence and accumulation characteristics of PAEs, surface water samples were collected from the Three Gorges Reservoir area, China. The total concentrations of 11 analyzed PAEs (∑ 11 PAEs) in the collected water samples ranging from 197.7 to 1,409.3 ng/L (mean ± IQR: 583.1 ± 308.4 ng/L). While DEHP was the most frequently detected PAE, DnBP and DnNP were the most predominant PAEs in the analyzed water samples with a mean contribution of 63.3% of the ∑ 11 PAEs. The concentrations of the ∑ 11 PAEs in the water samples from the upper reaches of the Yangtze River were significantly higher than those from the middle reaches. To better understand the transport and fate of the PAEs, seven detected PAEs were modeled by Quantitative Water Air Sediment Interaction (QWASI). The simulated and measured values were close for most PAEs, and differences are within one order of magnitude even for the worst one. For all simulated PAEs, water and particle inflow were main sources in the reservoir, whereas water outflow and degradation in water were important removal pathways. The contribution ratios of different sources/losses varied from PAEs, depending on their properties. The calculated risk quotients of DnNP in the Three Gorges Reservoir area whether based on monitoring or simulating results were all far exceeded the safety threshold value, implying the occurrence of this PAE compound may cause potential adverse effects for the aquatic ecology of the Three Gorges Reservoir area., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2024. Published by Elsevier B.V.)

Summertime surface ozone in China has been increasing since 2013 despite the policy-driven reduction in fuel combustion emissions of nitrogen oxides (NO x ). Here we examine the role of soil reactive nitrogen (N r , including NO x and nitrous acid (HONO)) emissions in the 2013-2019 ozone increase over the North China Plain (NCP), using GEOS-Chem chemical transport model simulations. We update soil NO x emissions and add soil HONO emissions in GEOS-Chem based on observation-constrained parametrization schemes. The model estimates significant daily maximum 8 h average (MDA8) ozone enhancement from soil N r emissions of 8.0 ppbv over the NCP and 5.5 ppbv over China in June-July 2019. We identify a strong competing effect between combustion and soil N r sources on ozone production in the NCP region. We find that soil N r emissions accelerate the 2013-2019 June-July ozone increase over the NCP by 3.0 ppbv. The increase in soil N r ozone contribution, however, is not primarily driven by weather-induced increases in soil N r emissions, but by the concurrent decreases in fuel combustion NO x emissions, which enhance ozone production efficiency from soil by pushing ozone production toward a more NO x -sensitive regime. Our results reveal an important indirect effect from fuel combustion NO x emission reduction on ozone trends by increasing ozone production from soil N r emissions, highlighting the necessity to consider the interaction between anthropogenic and biogenic sources in ozone mitigation in the North China Plain.

Black carbon (BC) plays a vital role in Arctic warming. Extensive investigations have been conducted to elucidate the source-receptor relationships of BC between the Arctic and mid-/high-latitude sources. However, it is unclear to what extent source relocation under globalization could disturb Arctic BC contamination and climate forcing from anthropogenic BC emissions. Here, we show that the global supply chain (GSC) relocation featured by the southward shift of industries from high-latitude developed countries to low-latitude developing countries markedly reduces the BC burden in the Arctic using a global chemical transport model (GEOS-Chem) and a multiregional input-output analysis (MRIO). We find that Arctic annual mean BC concentration associated with the GSC relocation drops by ∼15% from the case without the GSC relocation. The total net BC level declines 7% over the entire Arctic and 16% in the European Arctic. We also observed markedly declining BC deposition as well as direct and snow albedo radiative forcing in the Arctic. We show that the Arctic BC burden would be further reduced by decreasing BC emissions in China, attributable to its emission reduction and ongoing shift of the GSC from China to southern and southeastern Asia.

Due to the complexity of the environmental matrix and the limitation of the detection level, it is important to use models to evaluate environmental exposure to nanomaterials. Based on this, this research established two multi-media fate and transport models of silver nanoparticles (AgNPs) with respective coarse and fine spatial resolutions. Using the case of the spatial distribution of AgNPs in the Xiangjiang River, China, we compared how the spatial resolution of a model impacts modeling results. The results show that the process of heterogeneous aggregation has the greatest impact on the modeled concentration of AgNPs in water, and the heterogeneous aggregation of free AgNPs with natural colloids and settling down to sediments is the dominant mechanism responsible for the loss of AgNPs. In addition, the use of different spatial resolutions gives similar trends in the modeled AgNPs concentration, despite the difference in absolute levels. Our work also shows that the reliability and accuracy of the rate constant of heterogeneous aggregation has a great influence on the modeled AgNPs concentrations.

A modified community multiscale air quality model, which can simulate the regional distributions of 2,3-dihydroxy-4-oxopentanoic acid (DHOPA), a marker species for monoaromatic secondary organic aerosol (SOA), was applied to assess the applicability of using the DHOPA to aromatic SOA mass ratio ( f SOA ) from smog chamber experiments to estimate aromatic SOA during a three-week wintertime air quality campaign in urban Shanghai. The modeled daily DHOPA concentrations based on the chamber-derived mass yields agree well with the organic marker field measurements ( R = 0.79; MFB = 0.152; and MFE = 0.440). Two-thirds of the DHOPA are from the oxidation of ARO1 (lumped less-reactive aromatic species; mostly toluene), with the rest from ARO2 (lumped more-reactive aromatic species; mostly xylenes). Modeled DHOPA is mainly in the particle phase under ambient organic aerosol (OA) loading but could exhibit significant gas-particle partitioning when a higher estimation of the DHOPA vapor pressure is used. The modeled f SOA shows a strong dependence on the OA loading when only semivolatile aromatic SOA components are included in the f SOA calculations. However, this OA dependence becomes weaker when non-volatile oligomers and dicarbonyl SOA products are considered. A constant f SOA value of ∼0.002 is determined when all aromatic SOA components are included, which is a factor of 2 smaller than the commonly applied chamber-based f SOA value of 0.004 for toluene. This model-derived f SOA value does not show much spatial variation and is not sensitive to alternative estimates of DHOPA vapor pressures and SOA yields, and thus provides an appropriate scaling factor to assess aromatic SOA from DHOPA measurements. This result helps refine the quantification of SOA attributable to monoaromatic hydrocarbons in urban environments and thereby facilitates the evaluation of control measures targeting these specific precursors.

Cadmium (Cd) contamination in soil-rice systems has become a global public concern. However, influencing factors and the contamination threshold of Cd in soils remain largely unknown owing to soil heterogeneity, which limits our ability to assess the risk to human health and to draft appropriate environmental policies. In this study, we selected the soil-rice system of Longtang and Shijiao town in southern China, which was characterized by multi-metal acidic soil contamination due to improper electronic waste recycling activities, as a case to analyze the influence of different soil properties on the Cd threshold in the soil and Cd accumulation in rice. The results showed that soil organic matter (SOM) was the main factor regulating Cd accumulation in the soil-rice system. Moreover, compared with the total Cd concentration, the DTPA-extractable Cd concentration in the soil was a better predictor of Cd transportation in the soil-rice system. According to the prediction model, when SOM was < 35 g kg -1 , the Cd DTPA threshold was 0.16 mg kg -1 with a 95% likelihood of Cd rice accumulation above the Chinese food standard limit (0.2 mg kg -1 ). Conversely, when SOM was ≥ 35 g kg -1 , the Cd DTPA threshold was only 0.03 mg kg -1 . This study of the influence of SOM on Cd accumulation in a soil-rice system confirms that SOM is a crucial parameter for better and safer rice production, especially in multi-metal contaminated acidic soils., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Efforts of using data assimilation to improve PM 2.5 forecasts have been hindered by the limited number of species and incomplete vertical coverage in the observations. The common practice of initializing a chemical transport model (CTM) with assimilated initial conditions (ICs) may lead to model imbalances, which could confine the impacts of assimilated ICs within a day. To address this challenge, we introduce an initial error transport model (IETM) approach to improving PM 2.5 forecasts. The model describes the transport of initial errors by advection, diffusion, and decay processes and calculates the impacts of assimilated ICs separately from the CTM. The CTM forecasts with unassimilated ICs are then corrected by the IETM output. We implement our method to improve PM 2.5 forecasts over central and eastern China. The reduced root-mean-square errors for 1-, 2-, 3-, and 4-day forecasts during January 2018 were 51.2, 27.0, 16.4, and 9.4 μg m -3 , respectively, which are 3.2, 6.9, 8.6, and 10.4 times those by the CTM forecasts with assimilated ICs. More pronounced improvements are found for highly reactive PM 2.5 components. These and similar results for July 2017 suggest that our method can enhance and extend the impacts of the assimilated data without being affected by the imbalance issue.

Environmental humidity has a significanteffect on changes in free 220 Rn (thoron) production rate and effective diffusion coefficient of 220 Rn in uranium tailings. To understand such changes, a closed cavity containing porous 220 Rn media with finite thickness was studied. Based on the 220 Rn diffusion migration theory in porous media with finite thickness, a model for calculating the uniform 220 Rn activity concentration in a closed container with porous media of finite thickness was established. A laboratory method for concurrently determining free 220 Rn production rate and effective diffusion coefficient of 220 Rn was proposed and a corresponding experimental setup was made. With samples taken from a uranium tailing impoundment in southern China, water content, free 220 Rn production rate, and effective diffusion coefficient of 220 Rn in uranium tailings were determined under certain environmental temperature and humidity conditions. Results show that: (1) The method and experimental setup presented in this study can simultaneously determine free 220 Rn production rate and effective diffusion coefficient of 220 Rn in porous media such as uranium tailing; (2) The free 220 Rn production rate in uranium tailings increases linearly with water saturation. Effective diffusion coefficient of 220 Rn, on the other hand, decreases exponentially with the increase in water saturation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study investigated phosphorus (P) dynamics in the sediment-water interface of three distinct reservoirs located in a tropical semiarid region. Sequential chemical fractioning of the P content in the sediment and controlled experiments of the sediment-water interface were performed to understand and model the effect of the different P fractions on the exchange dynamics under anoxic and oxic scenarios. The results revealed that the older the reservoir, the higher the amount of iron and aluminum-bound P in the sediment, and that this fraction was responsible for a 10-fold increase in P concentration in the water during anoxic conditions. After aeration, P in water decreased but did not return to its initial concentration. The most recently constructed reservoir showed the lowest P concentration in the sediment and dominance of the unavailable P fraction, resulting in no potential impact on water quality. Phosphorus release and precipitation rates were well described by zero- and first-order models, respectively. Reservoirs with high P availability in the sediment, not only released more phosphorus but also presented a lower precipitation rate, resulting in higher potential damage to water quality and making some in-lake treatment techniques potentially ineffective., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Soil dissolved organic matter (DOM) plays an essential role in the Three Gorges Reservoir (TGR) as a linkage between terrestrial and aquatic systems. In particular, the reducing capacities of soil DOM influence the geochemistry of contaminants such as mercury (Hg). However, few studies have investigated the molecular information of soil DOM and its relationship with relevant geochemical reactivities, including redox properties. We collected samples from eight sites in the TGR areas and studied the link between the molecular characteristics of DOM and their electron donation capacities (EDCs) toward Hg(II). The average kinetic rate and EDC of soil DOM in TGR areas were (0.004 ± 0.001) hr -1 and (2.88 ± 1.39) nmol e - /mg DOM bulk , respectively. Results suggest that higher EDCs and relatively rapid kinetics were related to the greater electron donating components of lignin-derived and perhaps pyrogenic DOM, which are the aromatic constituents that influenced the reducing capacities of DOM in the present study. Molecular details revealed that even the typical autochthonous markers are important for the EDCs of DOM as well, in contrast to what is generally assumed. More studies identifying specific DOM molecular components involved in the abiotic reduction of Hg(II) are required to further understand the relations between DOM sources and their redox roles in the environmental fate of contaminants., (Copyright © 2019. Published by Elsevier B.V.)

Bauxite residue is the by-product of the aluminium industry with an annual output of more than 200 million metric tons in China. Its treatment is still a big problem because more than 96% of that is stockpiled on land causing environmental pollution and threatening the human health. This study used bauxite residue to remove Cr (Ⅲ) from aqueous solution and analyzed the removal mechanism. The removal time was dependent on the initial concentrations of Cr (Ⅲ) and different active components acted on different reaction period. Reaction time increased from <5 min to >2 h with an increase of Cr (Ⅲ) concentration from 5 to 100 and 170 mg/L. The existing forms of adsorbed-Cr were iron oxide-bound Cr (40.80%-87.85%), sulfide-bound Cr (4.04%-20.28%) and residue (6.60%-33.72%). All the components started to react as soon as bauxite residue was added. Cr did not precipitate in the presence of high alkalinity bauxite residue due to the slow release of alkalinity maintaining pH < 6, thus producing Cr(OH) 2+ , Cr 2 (OH) 2 4+ and Cr 3 (OH) 4 5+ by hydrolysis without precipitation. Fe 2 O 3 and Al-containing components were the main active phases for Cr (Ⅲ) removal, with the reaction time lasting more than 2 h and producing Ca 6 Al 4 Cr 2 O 15 , AlCr 2 , (Si, Al) 2 O 4 , Fe(Cr, Al) 2 O 4 , FeCr 2 Si 3 O 12 , MgCr 0·1 Fe 1·9 O 4 and MgCr 0·4 Fe 1·6 O 4 . Finally, bauxite residue was granulated and used for column tests. Cr (Ⅲ) wastewater (1 and 50 mg/L) was treated and the effluent can meet the first level of the Shanghai standard (0.1 mg/L) defined by Integrated Wastewater Discharge Standard (DB 31/199-2009)., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A recent quantitative measurement of rates of new particle formation (NPF) in urban Shanghai showed that the high rates of NPF can be largely attributed to the sulfuric acid (SA)-dimethylamine (DMA) nucleation due to relatively high DMA concentration in urban atmosphere (Yao et al., Science. 2018, 361, 278). In certain atmospheric conditions, the release of DMA is accompanied with the emission of high concentration of ammonia. As a result, the ammonia (A) may participate in SA-DMA-based NPF. However, the main sources of DMA and A can be different, thereby leading to different mechanism for the SA-DMA-A-based nucleation under different atmospheric conditions. Near industrial sources with relatively high DMA concentration of 10 8 molecules cm -3 , the contribution of binary SA-DMA nucleation to cluster formation is 61% at 278 K, representing a dominant pathway for NPF. However, in the region not too close to major source of DMA emission, e.g., near agriculture farmland, the routes involving ternary SA-DMA-A nucleation make a 64% contribution at 278 K with DMA concentration of 10 7 molecules cm -3 , showing that A has marked impact on the cluster formation. Under such a condition, we predict that coexisting DMA and A could be detected in the process of NPF. Moreover, at winter temperatures or at higher altitudes, our calculations suggest that the clustering of initial clusters likely involve ternary SA-DMA-A clusters rather than binary SA-DMA clusters. These new insights may be helpful to analyze and predict atmospheric-condition-dependent NFP in either urban or rural regions and/or in different season of the year., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

With the growing interest in alternative medicine, handy identification and differentiation of herbal medicines are becoming increasingly important. Here we report a chemometric modeling-free near infrared (NIR) barcode strategy for the smart identification and geographical origin discrimination of Chinese ginseng. The novel strategy demands the transformation of Chinese ginseng (standard and sample) NIR spectra into a barcode representation through assigning zero intensity to every NIR peak except the peaks having intensities greater than average peak intensity. Meanwhile, for Chinese ginseng standard NIR barcode, barcoding condition such as padding size was carefully optimized. It has been demonstrated that the padding size for each bar in the barcode is 8 cm -1 . By comparing the percentage of nonzero overlap between Chinese ginseng standard barcode and sample barcodes, eight batches of samples (including Chinese ginseng, American ginseng and counterfeit) were successfully identified with 100% accuracy, respectively. Interestingly, the discrimination of the origin of ginsengs from three provinces (Jilin, Liaoning and Heilongjiang) of Northeastern China was achieved utilizing NIR barcode method. Two characteristic bars at 7750 and 8250 cm -1 were inspected in the ginseng sample from Jilin province, two specific bars at 6780 and 7015 cm -1 were displayed in the ginseng sample from Liaoning province and three distinct bars at 6560, 6910 and 7995 cm -1 were monitored in the ginseng sample from Heilongjiang province. The results indicate that the proposed method will be greatly expanded and applied as an inspecting platform for the on-site analysis and valid identification of Chinese ginseng in herbal markets by a handheld spectrometer or barcode scanner., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Massive investments in energy industry may either promote or mitigate the air pollution which is likely to influence the economic performance. In light of this, the current work is an empirical examination of heterogeneous dynamic causal interactions among energy investment, sulphur dioxide (SO 2 ) emissions and economic growth in regional China. A modified STIRPAT model is developed to introduce energy investment as a determinant of technology. Based on a modified model, a simultaneous equations system has been established to examine the three-way causal interactions among the variables of interest. As a first step, an error-correction-based second generation Westerlund (Oxford Bulletin of Economics and Statistics 69: 0305-9049, (2007). cointegration has been employed and found the long-run relationship. The simultaneous equations have been estimated by employing second generation dynamic common correlated effects mean group estimator (DCCEMGE) for 30 Chinese provinces and cities from 2001 to 2017. The empirical analysis has revealed that the energy investment induces emissions promotion effect while economic growth introduces emissions curtailment effect. However, the emissions curtailment effect remained slightly stronger than emissions promotion effect both at country and regional levels. Further, the energy investment growth uncovered economic performance enhancement effect. Furthermore, the SO 2 emissions growth induced economic performance deterioration effect. In this regard, the economic performance deterioration effect exceeded the economic performance enhancement effect. Besides, there is a bidirectional causality operative between SO 2 emissions and gross regional product (GRP) growth for the country as well as regional samples. On the contrary, a positive bilateral causal relationship between energy investment and GRP growth is found for the country as well as regional samples. Similarly, it has been found that there exists a positive bilateral causal association between SO 2 emissions and energy investment. Graphical abstract.

The volatility of atmospheric aerosols greatly influences the gas-particle partitioning, chemical mechanisms and lifetime of aerosols. Due to the complex composition, the volatility of organic aerosol is one of the major sources of uncertainty in measuring and modeling ambient aerosols. Despite high aerosol loading in the atmosphere in China, especially in winter, few field measurements were conducted targeting the volatility of ambient organic aerosol (OA). With the deployment of a thermodenuder-aerosol mass spectrometer (TD-AMS) system, the volatility of non-refractory submicron aerosols (NR-PM 1 ) were measured on an island near the coastal line for the regional air in wintertime in southern China. NO 3 - and Cl - showed the highest volatility in the NR-PM 1 chemical species, while SO 4 2- showed the least volatility. Organic aerosol showed a moderate volatility, evaporating at a stable rate (0.57% °C -1 ) at temperatures lower than 150 °C and keeping a stable volatility when its loading increases, which could be an advantage for parameterization of OA in air quality models. Based on both positive matrix factorization and chemical mass balance modeling of OA composition, biomass burning OA was found to be the most volatile factor, followed by hydrocarbon-like OA and more-oxidized oxygenated OA. By summarizing the OA volatility measured in this study and in the literature, we found that the volatilities of different OA factors at different locations do not have a clear relationship with the OA oxidation state, possibly due to the vague understanding of local OA aging mechanisms and mixing states., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Uranium-contaminated wastewater associated with uranium (U) mining and processing inevitably releases into soil environment. In order to assess the risk of U wastewater contamination to groundwater through percolation, U adsorption and transport behavior in a typical red soil in South China was investigated through batch adsorption and column experiments, and initial pH and carbonate concentration were considered of the high-sulfate background electrolyte solution. Results demonstrated that U adsorption isotherms followed the Freundlich model. The adsorption of U to red soil significantly decreased with the decrease of the initial pH from 7 to 3 in the absence of carbonate, protonation-deprotonation reactions controlled the adsorption capacity, and lnC s had a linear relationship with the equilibrium pH (pH eq ). In the presence of carbonate, the adsorption was much greater than that in the absence of carbonate owing to the pH eq values buffered by carbonate, but the adsorption decreased with the increase of the carbonate concentration from 3.5 to 6.5 mM. Additionally, the breakthrough curves (BTCs) obtained by column experiments showed that large numbers of H + and CO 3 2- competed with the U species for adsorption sites, which resulted in BTC overshoot (C/C 0 > 1). Numerical simulation results indicated that the BTCs at initial pH 4 and 5 could be well simulated by two-site chemical non-equilibrium model (CNEM), whereas the BTCs of varying initial carbonate concentrations were suitable for one-site CNEM. The fractions of equilibrium adsorption sites (f) seemed to correlate with the fractions of positively charged complexes of U species in solution. The values of partition coefficients (k d ' ) were lower than those measured in batch adsorption experiments, but they had the same variation trend. The values of first-order rate coefficient (ω) for all BTCs were low, representing a relatively slow equilibrium between U in the liquid and solid phases. In conclusion, the mobility of U in the red soil increased with the decrease of the initial pH and with the increase of the initial carbonate concentrations.

A new sediment P release risk index (SPRRI) for "in-situ" phosphorus (P) release risk in lake sediment, is developed based on diffusive gradients in thin films (DGT) technique, DGT induced flux in sediments (DIFS) model and sediment properties. SPRRI includes three sub-indexes, which contain (1) the labile P pool size, (2) resupply constant (r) and desorption rate (Dspt rate) for P transfer and (3) the molar ratio between iron (Fe) in sequential extraction for sediment P by bicarbonate-dithionite (BD) and aluminum (Al) by NaOH (at 25 °C), i.e. BD(Fe)/Al[NaOH25] in sediment solid. The first sub-index considers P release from (i) sediment with NH 4 Cl-P+BD-P pool, i.e. the loosely sorbed P (NH 4 Cl-P) plus iron associated P (BD-P), or (ii) sediment with NH 4 Cl-P pool, respectively. The second and third sub-indexes reflect kinetic P desorption and resupply ability of solid phase, and the effect of P sequestration by Al hydroxide on P release, in turn. The inner relationship between SPRRI and sub-indexes, and their effects on P release risk are elucidated. SPRRI can be used to evaluate sediment P reactivity by five release risk ranks. For Lake Dianchi (China), P transfer dynamics, labile P pool, resupply ability and Al-P in sediment, and "external P-loading" control and affect P release risk in different regions, which is reflected by the spatial distribution map for SPRRI. The present SPRRI can be applied for lakes with (1) pH range varying from moderate acidity to weak alkalinity in waterbody and (2) NH 4 Cl-P or NH 4 Cl-P+BD-P pool in sediment solid., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In recent years, the concentration of fine particulate matter has decreased gradually in the Pearl River Delta (PRD) region, but the ozone (O 3 ) concentration remains high and has become the primary air pollutant. In this study, using a three-dimensional numerical model [nested air quality prediction modeling system (NAQPMS)] coupled with an on-line source apportionment module, the contribution of different source regions and source categories to the O 3 concentration in the PRD region was quantified. A comparison with observation data confirmed that the NAQPMS adequately reproduced surface O 3 concentrations in different seasons. Compared with biogenic emissions, anthropogenic precursors play a dominant role in O 3 production. In Guangzhou city, among different source categories, mobile emission is the largest contributor (accounting for approximately 40%), followed by industry emissions (20%-24%). Regional control measures for solvent use and mobile emissions are effective for reducing O 3 concentration. In the PRD region, self-contribution is more significant in daytime (∼40%) than in nighttime (∼10%) on average. Among the source regions outside PRD, the northern part of Guangdong province, Jiangxi province, and Fujian province are important contributors. Within the PRD region, the self-contribution of each city increases by 12%-32% during O 3 episodes (>80 ppbv) compared with the annual mean contribution. The contribution of the entire PRD region and the entire Guangdong province is 46%-63% and 63%-74% in PRD cities during O 3 episodes. These results indicate that regional collaboration on emission control within PRD or Guangdong province is effective for reducing O 3 episodes in the PRD region. In addition, because long-range transport from regions outside Guangdong province played an important role in the O 3 concentration in the PRD region, long-term emission control measures throughout China in subsequent years should be propitious to further reduce the annual O 3 level and improve air quality in the PRD region., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

As limited resources, soils are the largest terrestrial sinks of organic carbon. In this respect, 3D modelling of soil organic carbon (SOC) offers substantial improvements in the understanding and assessment of the spatial distribution of SOC stocks. Previous three-dimensional SOC modelling approaches usually averaged each depth increment for multi-layer two-dimensional predictions. Therefore, these models are limited in their vertical resolution and thus in the interpretability of the soil as a volume as well as in the accuracy of the SOC stock predictions. So far, only few approaches used spatially modelled depth functions for SOC predictions. This study implemented and evaluated an approach that compared polynomial, logarithmic and exponential depth functions using non-linear machine learning techniques, i.e. multivariate adaptive regression splines, random forests and support vector machines to quantify SOC stocks spatially and depth-related in the context of biodiversity and ecosystem functioning research. The legacy datasets used for modelling include profile data for SOC and bulk density (BD), sampled at five depth increments (0-5, 5-10, 10-20, 20-30, 30-50 cm). The samples were taken in an experimental forest in the Chinese subtropics as part of the biodiversity and ecosystem functioning (BEF) China experiment. Here we compared the depth functions by means of the results of the different machine learning approaches obtained based on multi-layer 2D models as well as 3D models. The main findings were (i) that 3rd degree polynomials provided the best results for SOC and BD (R2 = 0.99 and R2 = 0.98; RMSE = 0.36% and 0.07 g cm-3). However, they did not adequately describe the general asymptotic trend of SOC and BD. In this respect the exponential (SOC: R2 = 0.94; RMSE = 0.56%) and logarithmic (BD: R2 = 84; RMSE = 0.21 g cm-3) functions provided more reliable estimates. (ii) random forests with the exponential function for SOC correlated better with the corresponding 2.5D predictions (R2: 0.96 to 0.75), compared to the 3rd degree polynomials (R2: 0.89 to 0.15) which support vector machines fitted best. We recommend not to use polynomial functions with sparsely sampled profiles, as they have many turning points and tend to overfit the data on a given profile. This may limit the spatial prediction capacities. Instead, less adaptive functions with a higher degree of generalisation such as exponential and logarithmic functions should be used to spatially map sparse vertical soil profile datasets. We conclude that spatial prediction of SOC using exponential depth functions, in conjunction with random forests is well suited for 3D SOC stock modelling, and provides much finer vertical resolutions compared to 2.5D approaches., Competing Interests: The authors have declared that no competing interests exist.

This paper aims to assess the performance of a distributed hydrological model for simulating the transport of various heavy metals in rivers, to enhance and support environmental monitoring strategies for rivers in developing countries. In this context, we evaluated the performance of the Geophysical flow Circulation (GeoCIRC) model based on Object-Oriented Design (OOD) for the simulation of contamination from multiple heavy metals (Pb, Hg, Cr, and Zn) in Harrach River in Algeria. The results of the case study were in good agreement with the observations. Methodology for the assessment of data quality control and the improvement of monitoring procedures was proposed by using the hydrological model to simulate different scenarios. The GeoCIRC-model-based OOD allowed the prediction of the concentrations of heavy metals with minimal input data. Also, various heavy metals could be numerically treated simultaneously because the OOD increases the model's flexibility to allow the handling of many transportable materials. Therefore, the GeoCIRC model is a powerful tool for the monitoring of environmental contamination in rivers by various heavy metals.

Atmospheric particulate pollution in China has attracted much public attention. Occasionally, the particle number concentration increases sharply in a short time period, which is defined as a "particulate matter explosive increase". Heavy particulate matter pollution not only reduces visibility but also has an adverse effect on human health. Hence, there is an urgent need to discover the causes of particulate matter explosive increase. During this campaign, the particle number concentration and free radicals were measured at a tall building on the campus of Lanzhou University of Technology. Additionally, we examined a series of chemicals to reproduce the observed particulate matter explosive increase in a smog chamber to determine its potential factors. Then, we analyzed the mechanism of particulate matter explosive increase in the presence of free radicals. We found that, among the potential inorganic and organic sources analyzed, a mixture of organic and SO 2 in the research region had a major effect on particulate matter explosive increase. Moreover, free radical oxidation has a large effect, especially in the formation of organic particulates., (Copyright © 2019. Published by Elsevier B.V.)

The sorption behavior of selenite onto the Tamusu clay from a preselected high-level radioactive waste disposal site in Inner Mongolia, China, was first investigated in simulated groundwater with high salinity by batch sorption experiments under aerobic/anaerobic conditions. The results demonstrated that the K d values rapidly decreased and then remained steady in the pH range of 2.0-8.0. However, selenite sorption was promoted when pH exceeded 8.0, which might be attributed to the coprecipitation between Ca 2+ and SeO 3 2- . Besides, the change trend of the K d values as functions of various parameters was not affected by oxygen. The sorption kinetics and isotherms could be well fitted by the pseudo-second-order kinetic model and the Freundlich model for both aerobic and anaerobic conditions, and the calculated thermodynamic parameters (△G and △H) suggested that the selenite sorption process was a spontaneous and endothermic process. Additionally, the XPS results revealed that Se(IV) could be reduced to Se (0) only in anaerobic conditions and that the different amounts of Fe on the clay surface led to the discrepancy of the Se(IV) K d values under aerobic and anaerobic conditions even in high-salt simulated groundwater. Overall, our findings in this study are significant in regards to the retardation of selenite on the host rock under high salinity conditions., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Accurately measuring and estimating trends and variations in nutrient levels is a significant part of managing emerging eutrophic lakes in developing countries. This study developed an integrated approach containing Seasonal Trend Decomposition using Loess (STL) and a dynamic nonlinear autoregressive model with exogenous input (NARX) network to decompose and estimate the nutrient concentrations in Lake Erhai, a preliminary eutrophic lake in China. The STL decomposition results indicated that total nitrogen (TN) concentration of Lake Erhai progressively descended from 2006 to 2014, except for some agriculture area. The total phosphorus (TP) concentration showed an increasing trend from 2006 to 2013 and then decreased in 2014, but in the area near the tourist attractions, TP increased continuously from 2011 to 2014. Seasonal variations in TN and TP indicated that the lowest water quality of Lake Erhai occurred from July to October. Based on results obtained with STL, TP was selected as the sensitive parameter, as it showed a significant deterioration trend, and the area near the tourist attractions was selected as the sensitive area. Three variables (DO, pH, and water temperature) were selected as input parameters to estimate TP using the dynamic NARX model. The NARX modeling results demonstrated that it can accurately estimate TP concentrations with low root-mean-square error (0.0071 mg/L). The study establishes a new approach to better understand trends and variations in nutrient levels and to better refine estimates by identifying more easily accessible physical parameters in a preliminary eutrophic lake.

Eutrophication is a leading cause of impairment of lentic water bodies throughout the world. To inhibit algal blooms and remove excess nutrients, a 10,000 m 2 restoration project consisting of vegetation establishment and fish manipulation was conducted in the eutrophic bay of the Yantian Reservoir, southern China. Three Ecopath models were constructed to assess the recovery effects at an ecosystem level, and time series data were simulated to propose a fishery policy. During the restoration, 1) the redundant primary production flowing back to detritus decreased due to the increased predation of four stocked fish with different feeding habits; 2) the transfer efficiencies (TEs) through trophic levels increased due to the reinforced energy flows along the planktivorous, herbivorous, and molluscivorous food chains; 3) the groups that had the highest keystoneness shifted from carnivorous fish to invertivorous fish and omnivorous shrimp, indicating the shift of mixed trophic impacts from top-down to wasp-waist control; and 4) the changing indices of path length, flow fluxes, matter cycling, and network information showed that the restored system was more mature, developed, and organized than before. To sustain the long-term energy balance and functioning of the ecosystem, the maximum fishing yields (0.37-8.53 g/m 2 /year) were determined to maintain the relative biomass (close to 1) of stocked fish and wild tilapia by harvesting their annual production., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Simulation of ammonia (NH 3 ) volatilization by process-oriented biogeochemical models, such as the widely used DeNitrification DeComposition (DNDC), is an imperative need to identify the best management strategies that can improve nitrogen use efficiency in crop production while alleviating environmental pollution. However, scarce validation has been impeding the applicability of the DNDC for this purpose. Using the micrometeorological or wind tunnel-based observations of NH 3 volatilization in 44 cases with at seven nationwide field sites in China, which were cultivated with summer maize and winter wheat in calcareous soils and applied with synthetic fertilizers, the DNDC was tested, modified, and evaluated in this study. The following major modifications were made in the model source codes. Primarily, pedo-transfer functions were introduced into the model to provide three soil hydraulic parameters that are required to simulate soil moisture. Then, the temperature effect on ammonium bicarbonate decomposition, which was originally missing, was parameterized. Finally, the effect of soil texture on ammonia volatilization from the liquid phase was re-parameterized while an adaption factor was set. Seven typical cases were involved in the model modifications and the other 37 independent cases were used for the modified model evaluation. Compared to the original model, the modified DNDC performed better. For instance, it showed a higher index of agreement of 0.77 versus 0.38, a higher modeling efficiency (Nash-Sutcliffe index) of 0.19 versus -0.52, and a greater determination coefficient (R 2 ) of 0.35 (p < 0.001) versus no available value (i.e., R 2  ≤ 0) in the zero-intercept linear regression of the observed cumulative NH 3 volatilizations during individual measurement periods against the simulations. Future studies are needed to further improve the modified DNDC so as to better simulate the effects of rainfall/irrigation and deep placement of fertilizers on NH 3 volatilization from calcareous soils cultivated with upland crops., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The stainless steel pickling residue (SSPR) produced from the stainless steel industries in China contains large amounts of heavy metals such as chromium (Cr) and nickel (Ni). The study found that the hexavalent chromium Cr (VI) was the primary contributor to the leaching of Cr in the toxicity character leaching test. A chemical fixation with sodium sulfide was used to treat the SSPR, and the response surface methodology (RSM) was employed to optimize the process. The results revealed that the sodium sulfide dose and curing time had significant effects on the fixation of Cr. The higher was the sodium sulfide dose, and the longer the curing time, the lower the leaching concentration of Cr would be. The water addition amount had insignificant effect when it was higher than 70%. A dose of 1.2% sodium sulfide on dry mass basis, a water addition of 90-100%, and a curing time of longer than 10 days in the open air could reduce the leaching of Cr to below the beneficial use threshold. The low chemical dose and simple procedures established in this study make this treatment method cost-effective for rendering the SSPR into a nonhazardous and useful material.

Traditional models of nutrient simulation usually focus on the pollutant sources and precipitation, lacking the quantification of landscape structure. We developed a new prediction model of pollution risks by combing pollutant sources, precipitation, and landscape structure, which was defined as the source-precipitation-landscape model (SPLM). The SPLM was applied to simulate the non-point source (NPS) total nitrogen (TN) exports in one of the largest river basins in China (the Haihe River Basin, HRB). TN concentrations of 35 sampling catchments in 2013 were used to test the accuracy of the SPLM. Simulated results showed that (1) the SPLM had a relative high accuracy in the simulation of NPS TN export and intensity, especially for TN intensity. (2) The mean TN export and intensity of all the 1578 catchments in the HRB were 441.97 t and 2.08 t/km 2 , respectively. (3) The TN export intensities differed greatly among the sub-basins in the HRB, ranging from 0.64 to 6.81 t/km 2 . On the whole, the TN export intensities of the plain sub-basins (e.g., the Tuhaimajia River, the Heilonggang River, and the Beisihe River) were much higher than those of mountainous sub-basins (e.g., the Yongding River, the Beisanhe River, and the Luanhe River). (4) The contributions to TN exports, from high to low, were land use (38.82%), livestock husbandry (33.57%), and rural population (27.61%). Among all the ten pollution sources, arable land (30.87%), rural population (27.61%), and large livestock (17.73%) had the top three contributions to TN exports. This study provides a feasible tool for policymakers and administrators to develop workable management measures for the mitigation of NPS pollution. This SPLM can be extended to other regions in a rapid urbanization context.

Photocatalytic oxidation of formaldehyde (HCHO) is considered as one of the promising ways to resolve indoor air HCHO pollution. TiO 2 has been well known as the most extended application in photocatalysis due to its strong oxidizing ability and stability. Owing to high activity under visible light irradiation, TiO 2 and Bi 2 O 3 doping mixed with Bi 2 WO 6 was analyzed in this study. The formation of two kinds of heterojunction caused efficient charge separation, leading to the effective reduction in the recombination of photo-generated electron and hole. The special structure and enhanced performance of these catalysts were analyzed. For the first time, the loading of alkali salts was researched for photocatalytic oxidation. In order to understand the reaction mechanism of alkali salts enhanced effects, the catalysts were investigated by using BET, XRD, UV-Vis, FT-IR, SEM, and XPS. The results found more than 2 wt% of Na 2 SO 4 loading and the mixed methods with different solutions were key factors affecting the performance of catalysts. Nearly 92% HCHO conversion could be completed over Bi 2 WO 6 /Bi 0.15 Ti 0.85 O 2 (Na 2 SO 4 ), and the concentration of HCHO was only 0.07 mg/m 3 for 24 h, which was below the limit of specification in China. The results also indicated that the solution mixing method was more favorable to increase the HCHO conversion due to decrease the size of Bi 0.15 T i0.85 O 2 particles. The catalysts with Na 2 SO 4 loading provided more surface-adsorbed oxygen that facilitated the desorption of CO 2 and markedly increased the photocatalytic oxidation of HCHO. Graphical abstract Plausible mechanism over W-Bi2WO6/ Bi0.15Ti0.85O2-Na2SO4 (1:4) catalysts.

The concentrations and spatial occurrences of 17 legacy per- and polyfluoroalkyl substances (PFAS) and 4 emerging PFAS in the coastal water-dissolved phase, surface sediment phase and suspended particulate matter (SPM) in the coastal areas of Bohai Bay were investigated. In addition, the partition behaviors of PFAS in the water-SPM system and water-sediment system and the potential sources of PFAS in the marine environment were revealed. The total concentrations of PFAS (∑PFAS) in the water-dissolved phase, surface sediment and SPM were 20.5-684 ng/L, 2.69-25.0 ng/g dry weight (dw) and 4.39-527 ng/g dw, respectively. The level of PFAS contamination in the coastal areas of Shandong Province was higher than that in other areas. The average partition coefficients (log K d ) of PFAS in the water-SPM system and water-sediment system were 1.56-3.57 and 0.72-2.95, respectively. Long-chain PFAS and PFECHS (perfluoroethylcyclohexane sulfonate) have a higher log K d than that of short-chain PFAS. PFAS with short carbon chains were mainly detected in the water-dissolved phase, but long-chain PFAS mainly occurred in the surface sediment and SPM phases. Source analysis based on the positive matrix factorization (PMF) model found that erosion inhibitor factories, aqueous film-forming foam factories, metal plating plants, fluoropolymer chemical manufacture and food contact materials were the main sources of PFAS in Bohai Bay. These results improved our understanding of the partitioning behavior and sources of PFAS in aquatic environments., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

China is the biggest consumer of coal. Every year, half or more of China's coal is used in the power industry. Most thermal power plants in China use electrostatic precipitators to treat solid particulate matter in flue gas. The efficiency of the electrostatic precipitator in removing dust has a considerable influence on atmospheric pollutants. However, the most important factor affecting the efficiency of the electrostatic precipitator in removing dust is the dielectric properties of the fly ash. Through the study of volt-ampere characteristics, electrical and capacitive properties, and electrical breakdown characteristics of coal-fired fly ash, it is found that the V-I characteristics of ash samples in thermal power plant do not strictly follow the formula ([Formula: see text]), the type of coal, and the chemistry of coal. Ingredients are related; disparate types of ash samples have disparate capacitances, and the measurement of capacitive contrast resistance has a certain influence.

Methylmercury (MeHg) is a toxic compound. It forms mainly in reducing environments, and then degrades through biogeochemical processes. Photodegradation and microorganism degradation of MeHg are among the processes that have been reported. However, little attention has been focused on the abiotic degradation of MeHg in soil/sediment without light. In our study, the percent MeHg of total Hg in Guangzhou soil in southern China was found to be variable and exhibited a significant negative correlation with the content of Fe or Cu where annite (KFe 2+ 3 (AlSi 3 O 10 )(OH) 2 ), a Fe-bearing mineral, was identified. To understand the mechanisms of radical-initiated MeHg degradation by Fe/Cu-containing components, batch experiments were done. Results showed that annite in the soils could activate O 2 to generate OH and O 2 - and facilitate MeHg degradation under oxic conditions. Meanwhile, Cu components in the soil further enhanced the production of O 2 - , and was oxidized to Cu(III) promoting degradation of MeHg directly. These findings help us understand that the distribution of MeHg in soil depends on not only external pollution sources, but also on biogeochemical processes in subsurface environments., (Copyright © 2018. Published by Elsevier B.V.)

Slag heaps are formed by mining waste materials, and the improper treatment of leachate from such heaps can threaten nearby aquifers. The Zhehai slag heap in Yunnan Province, China, contains 2.7 million tons of zinc and cadmium slag, and is considered a heavy metal source threatening the local groundwater safety, however, the severity of contamination remains unknown. In this study, numerical modeling was used to predict the groundwater flow and contaminant transport in this area based on field data. The results show that the atmospheric precipitation infiltration recharge at the top of the heap is 81.8 m³/d, accounting for 93.76% of total infiltration. The south and east sides of the area are the main outflow channels for contaminants, accounting for 93.25% of the total discharge around the heap. To reduce aquifer contamination, an in situ system involving a "controlling the source, 'breaking' the path, and intercepting the flow" (CSBPIF) strategy is established. The results indicate that the system performs well because it not only decreases the flow velocity but also reduces the concentrations of contaminants adsorbed by clay media. Moreover, the equivalent bottom liner thicknesses of the clay layers were calculated to improve the applicability of the CSBPIF system. Compared with ex situ disposal, this scheme provides an economic and effective solution and can be used to prevent and control groundwater pollution in China.

Source inversion uses air dispersion models and environmental measurements to determine the atmospheric radionuclide release rate, which is critical in formulating an emergency response to nuclear incidents. Because source inversion methods are vulnerable to multiple uncertainties, site-specific validations that consider multiple air dispersion scenarios are important in ensuring their correct implementation. To comprehensively evaluate the ensemble Kalman filter (EnKF) for source inversion, a site-specific validation based on six wind tunnel experiments was performed for a highly heterogeneous nuclear power plant site in China. The six experiments cover the typical meteorology of the site and various topography types, providing abundant air dispersion scenarios for validation. The sensitivity of the EnKF to the initial guess, inflation factor, and position/number of measurements is also investigated. The results demonstrate that EnKF offers stable convergence and a reasonably bounded error in all experiments. Furthermore, the EnKF is insensitive to the initial guess, inflation factor, and number of measurements. However, it is sensitive to the position of the measurements and the air dispersion scenario. This sensitivity results from the complicated biases in air dispersion models, which highlight the key to improving the performance of EnKF., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Ambient exposure to fine particulate matter (PM 2.5 ) is known to harm public health in China. Satellite remote sensing measurements of aerosol optical depth (AOD) were statistically associated with in-situ observations after 2013 to predict PM 2.5 concentrations nationwide, while the lack of surface monitoring data before 2013 have created difficulties in historical PM 2.5 exposure estimates. Hindcast approaches using statistical models or chemical transport models (CTMs) were developed to overcome this limitation, while those approaches still suffer from incomplete daily coverage due to missing AOD data or limited accuracy due to uncertainties of CTMs. Here we developed a new machine learning (ML) model with high-dimensional expansion (HD-expansion) of numerous predictors (including AOD and other satellite covariates, meteorological variables and CTM simulations). Through comprehensive characterization of the nonlinear effects of, and interactions among different predictors, the HD-expansion parameterized the association between PM 2.5 and AOD as a nonlinear function of space and time covariates (e.g., planetary boundary layer height and relative humidity). In this way, the PM 2.5 -AOD association can vary spatiotemporally. We trained the model with data from 2013 to 2016 and evaluated its performance using annually-iterated cross-validation, which iteratively held out the in-situ observations for a whole calendar year (as testing data) to examine the predictions from a model trained by the rest of the observations. Our estimates were found to be in good agreement with in-situ observations, with correlation coefficients (R 2 ) of 0.61, 0.68, and 0.75 for daily, monthly and annual averages, respectively. To interpolate the missing predictions due to incomplete AOD data, we incorporated a generalized additive model into the ML model. The two-stage estimates of PM 2.5 sacrificed the prediction accuracy on a daily timescale (R 2  = 0.55), but achieved complete spatiotemporal coverage and improved the accuracy of monthly (R 2  = 0.71) and annual (R 2  = 0.77) averages. The model was then used to predict daily PM 2.5 concentrations during 2000-2016 across China and estimate long-term trends in PM 2.5 for the period. We found that population-weighted concentrations of PM 2.5 significantly increased, by 2.10 (95% confidence interval (CI): 1.74, 2.46) μg/m 3 /year during 2000-2007, and rapidly decreased by 4.51 (3.12, 5.90) μg/m 3 /year during 2013-2016. In this study, we produced AOD-based estimates of historical PM 2.5 with complete spatiotemporal coverage, which were evidenced as accurate, particularly in middle and long term. The products could support large-scale epidemiological studies and risk assessments of ambient PM 2.5 in China and can be accessed via the website (http://www.meicmodel.org/dataset-phd.html)., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In China, fine particulate matter (PM 2.5 ) and ground-level ozone (O 3 ) are anticipated to continuously affect large populations in the coming decades. Simulations of the levels of these pollutants largely depend on emissions inputs, which are highly uncertain both in magnitude and spatial distribution. Our goal was to explore sensitivities of projected changes in PM 2.5 - and O 3 -related short-term health impacts in mainland China to emissions and other model inputs. We simulated winter PM 2.5 and summer O 3 concentrations using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) for both 2008 and 2050. We used three emission inventories in 2008 and four emissions scenarios in 2050. The resulting air pollutant concentrations were combined with eight population projections and three concentration-response functions (CRFs) to estimate future PM 2.5 - and O 3 -related health impacts including total, cardiovascular, and respiratory mortalities in mainland China. Multivariate analysis of variance was used to apportion the uncertainty due to different model parameters. Combinations of different parameters produced a wide range of national PM 2.5 - and O 3 -related mortalities. CRFs and present emissions each contribute 38%-56% and 20%-28% of the total sum of squares for PM 2.5 -related mortalities. Future emissions are the largest source of uncertainty in O 3 -related mortality estimates, contributing 24%-48% of total sum of squares. Our results suggest that conducting more epidemiological studies and constraining the present day emissions are essential for projecting future air pollutant-related health impacts in mainland China., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Emissions of polycyclic aromatic hydrocarbons (PAHs) in China remain at a high level compared to those in developed countries. The Yangtze River Delta (YRD) is an economic and industrial center in China with an extremely large population. The potentially high emissions and excess cancer risk from human exposure in this region cannot be neglected. This study applied a multimedia model to estimate the concentrations of 16 US EPA priority PAHs in the environment in the YRD with a well-developed PAH-emission inventory for 2014. The model predicted that the average concentrations of ΣPAHs were 274 ng/m 3 in the air, 255 ng/g in the soil, 15 ng/g in vegetation, 147 ng/L in freshwater and 144 ng/g in sediment, as well as 99 ng/L and 80 ng/g in seawater and sediment, respectively. Soil is the PAH sink in this region, and the net flux of the total PAHs is always from air to soil for each isomer. A deterministic assessment observed that the ELCR (excess lifetime cancer risk) ranged from 2.5 × 10 -6 to 3.0 × 10 -5 for exposure by air inhalation and from 3.5 × 10 -7 to 7.9 × 10 -6 for exposure by soil ingestion. The probabilistic results did not find any probability of ELCR >10 -4 by exposure via soil ingestion in the YRD. The probabilistic ELCR induced by inhalation exposure varied from 8.1 × 10 -7 to 3.1 × 10 -4 in the YRD. This study provided a comprehensive overview of PAHs occurrence in natural environments and of the relevant human health risks. The information presented in this study could help authorities to enact a strategy regarding emission reduction and pollution control relevant to PAHs., Capsule: Multimedia modeling predicted distributions and compositions of PAHs in different environmental compartments, and deterministic and probabilistic ELCRs induced by air inhalation and soil ingestion were also provided., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Excessive nitrogen (N) loadings from human activities have led to increased eutrophication and associated water quality impacts in China's coastal wetlands. Denitrification accounts for significant reduction of inorganic N to nitrous oxide (N 2 O) or dinitrogen gas (N 2 ), and thereby curtails harmful effects of N pollution in coastal and marine ecosystems. However, the molecular drivers and limiting steps of denitrification in coastal wetlands are not well understood. Here, we quantified the abundances of functional genes involved in N cycling and determined denitrification rates using 15 N paring technique in the coastal wetland sediments of Bohai Economic Rim in eastern China. Denitrification accounting for 80.7 ± 12.6% of N removal was the dominant pathway for N removal in the coastal wetlands. In comparison, anaerobic ammonium oxidation (ANAMMOX) removed up to 36.9 ± 7.3% of inorganic N. Structural equation modeling analysis indicated that the effects of ammonium on denitrification potential were mainly mediated by the relative abundances of nosZ/nirS, nirS/(narG + napA) and amoA/nirK. Denitrification was limited by the relative strength of two steps, namely N 2 O reduction to N 2 and nitrite (NO 2 - ) reduction to nitric oxide (NO). Our results suggest that the relative abundances of functional genes which are more stable than sediment chemical compounds in the context of environmental changes are indictive of denitrification potential in coastal wetlands., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Floodplain lakes are valuable to humans because of their various functions and are characterized by dramatic hydrological condition variations. In this study, a two-dimensional coupled hydrodynamic and water quality model was applied in a large floodplain lake (i.e., Poyang Lake), to investigate spatial and temporal water quality variations. The model was established based on detailed data such as lake terrain, hydrological, and water quality. Observed lake water level and discharge and water quality parameters (TN, TP, COD Mn , and NH 4 -N) were used to assess model performance. The hydrodynamic model results showed satisfactory results with R 2 and MRE values ranging between 0.96 and 0.99 and between 2.45 and 6.14%, respectively, for lake water level simulations. The water quality model basically captured the temporal variations in water quality parameters with R 2 of TN, TP, COD Mn , and NH 4 -N simulation ranges of 0.56-0.91, 0.44-0.66, 0.64-0.67, and 0.44-0.57, respectively, with TP of Xingzi Station and COD Mn of Duchang Station excluded, which may be further optimized with supplementation of sewage and industrial discharge data. The modeled average TN, TP, COD Mn , and NH 4 -N concentrations across the lake were 1.36, 0.05, 1.99, and 0.48 mg/L, respectively. The modeled spatial variations of the lake showed that the main channel of the lake acted as a main pollutant passageway, and the east part of the lake suffered high level of pollution. In addition, consistent with previous water quality evaluations based on field investigations, water quality was the highest (average TN = 1.35 mg/L) during high water level periods and the poorest (average TN = 1.96 mg/L) during low water level periods. Scenario analysis showed that by decreasing discharge of upstream flow by 20% could result in the increase of TN and TP concentrations by 25.6% and 23.2% respectively. In summary, the model successfully reproduced the complex water and pollutant exchange processes in the systems involving upstream rivers, the Poyang Lake, and the Yangtze River. The model is beneficial for future modeling of the impact of different load reduction and other hydrological regime changes on water quality variation and provides a relevant example for floodplain lake management.

With the rapid urbanization and increasing urban impervious areas in China, urban water-logging has become increasingly serious. The concept of sponge city was proposed based on the low impact development (LID) idea. We analyzed the impacts of landscape pattern optimization scenario on urban surface runoff and rainwater control ability in central urban area of Shen-Fu New Town in Liaoning Province. The storm intensity formula was used to construct rainfall process in different return periods. The landscape patterns of the study area were optimized based on sponge city concept. The storm water management model (SWMM) was used to simulate the differences of surface runoff and rainwater regulation ability under the pre-planning scenario and the landscape pattern optimization scenario. The results showed that total runoff and runoff coefficient of the study area were increased with increasing rainfall return period. In the same rainfall return period, the runoff coefficient was significantly reduced. The reduction of total runoff gradually increased, being 2.94, 3.58, 3.72, and 4.19 mm during the 1-year, 3-year, 5-year and 50-year return period under landscape pattern optimization scenario. The corresponding reduction rate was gradually reduced, being 23.9%, 16.4%, 14.3%, and 9.3%, respectively. Landscape pattern optimization scenario could meet the requirements that the rainfall was controlled at 20.8 mm when the rainfall return period p=1 year, the rainwater pipe network would not overload when p=3 years, and the river channel would not overflow when p=50 years.