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Isotopic Compositions (Li-B-Si-O-Mg-Sr-Nd-Hf-Pb) and Fe2+/sigma Fe Ratios of Three Synthetic Andesite Glass Reference Materials (ARM-1, ARM-2, ARM-3)
No full textTo expand the newly developed ARM glasses as reference materials for in situ microanalysis of isotope ratios and iron oxidation state by a variety of techniques such as SIMS, LA-MC-ICP-MS and EPMA, we report Li-B-Si-O-Mg-Sr-Nd-Hf-Pb isotope data and Fe2+/sigma Fe ratios for these glasses. The data were mainly obtained by TIMS, MC-ICP-MS, IR-MS and wet-chemistry colorimetric techniques. The quality of these data was cross-checked by comparing different techniques or by comparing the results from different laboratories using the same technique. All three glasses appear to be homogeneous with respect to the investigated isotope ratios (except for B in ARM-3) and Fe2+/sigma Fe ratios at the scale of sampling volume and level of the analytical precision of each technique. The homogeneity of Li-B-O-Nd-Pb isotope ratios at the microscale (30-120 mu m) was estimated using LA-MC-ICP-MS and SIMS techniques. We also present new EPMA major element data obtained using three different instruments for the glasses. The determination of reference values for the major elements and their uncertainties at the 95% confidence level closely followed ISO guidelines and the Certification Protocol of the International Association of Geoanalysts. The ARM glasses may be particularly useful as reference materials for in situ isotope ratio analysis
Effects of Ice Freeze-Thaw Processes on U Isotope Compositions in Saline Lakes and Their Potential Environmental Implications
No full textThe dissolved uranium (U) content in the water column of saline lakes varies little between ice-free seasons throughout the whole water column. Such uniformity allows for the potential absolute dating and/or paleohydrologic interpretations of lake sediments and biogenic shell materials using U isotopes. Before using these methods in cold regions, however, it is necessary to evaluate the effects that ice freeze-thaw processes have on the distribution of U isotopes in saline lake waters, and to determine the amount of variation in U isotopic values when such processes occur. In this paper, we collected ice and dissolved water samples from six lakes with variable salinity in February 2021. Five groundwater and three water samples from rivers into Qinghai Lake were sampled in November 2020. The sampled water was analyzed for dissolved concentrations of U-238 and the activity ratio of U-234/U-238 ([U-234/U-238](AR)). The results show that the U-238 concentration of ice samples was less than that of the underlying water. The [U-234/U-238](AR) of ice in the five saline lakes was similar to that of the underlying water with less than a 10 parts per thousand variation, suggesting no observable fractionation between ice and dissolved water. Thus, the ice freeze-thaw processes have almost no effect on the uranium content and [U-234/U-238](AR) of the sampled saline lakes, which were characterized by a limited recharge volume from surface runoff, groundwater, and ice volume, namely the close saline lake in arid alpine background. The results from the indoor freeze-thaw experiments also showed that the U isotopic composition of Qinghai Lake waters and ice were similar with the U-238 concentration of the ice was about 40% of that of the dissolved lake water, supporting the data obtained from natural saline lakes. The above results provide important insights into whether it is feasible to use U isotopes for absolute dating and/or paleohydrologic analysis of lake sediments or biogenic shell materials. In addition, the results are important for evaluating the [U-234/U-238](AR) and uranium concentrations in seawater when there exists a process of melting polar ice, and for determining the initial delta U-234 variations needed for dating of coral and other fossil materials
Oxygen vacancy defects-boosted deep oxidation of NO by beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst in situ synthesized from Bi/Ce(CO3) (OH) precursor
No full textFlower-like n-type CeO2-delta is hybridized with p-type beta-Bi2O3 nanoparticles to design a novel beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst via a thermal treatment process of Bi/Ce(CO3)(OH) precursor. The synthesized beta-Bi2O3/CeO2-delta exhibits a remarkable enhancement in NO removal and significant suppression of toxic intermediates nitrogen dioxide (NO2) under visible light irradiation. The superior photocatalytic activity of beta-Bi2O3/CeO2-delta for NO removal is mainly derived from the synergistic effects of the oxygen vacancies (OVs) and p-n heterojunction. The OVs not only enhance the visible light utilization and boost the separation of electronhole pairs but also improve the adsorption and activation of NO and O-2. Particularly, the p-n heterojunction is beneficial for the interfacial migration of photogenerated charge carriers. Electron spin resonance (ESR) and trapping experiment reveal that the synergistic effects of OVs and p-n heterojunction can induce the generation of more active species. The electrochemical measurements and density-functional theory (DFT) calculations indepth confirm that both p-n heterojunction and OVs can accelerate the interfacial charge transfer, resulting in the deep oxidation of reactants. Therefore, the flower-like beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst exhibits an advanced photocatalytic activity for deep NO removal and a suppressed NO2 generation. In addition, monitoring the reaction products by in situ Fourier transform infrared spectrum (FTIR) further validates that the main products of nitrates are formed during the photocatalytic process. This work demonstrates a straightforward approach for construction of p-n heterojunction photocatalysts, which can enhance the effective photocatalytic activity and stability for NO removal
Oxygen vacancy defects-boosted deep oxidation of NO by beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst in situ synthesized from Bi/Ce(CO3) (OH) precursor
No full textFlower-like n-type CeO2-delta is hybridized with p-type beta-Bi2O3 nanoparticles to design a novel beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst via a thermal treatment process of Bi/Ce(CO3)(OH) precursor. The synthesized beta-Bi2O3/CeO2-delta exhibits a remarkable enhancement in NO removal and significant suppression of toxic intermediates nitrogen dioxide (NO2) under visible light irradiation. The superior photocatalytic activity of beta-Bi2O3/CeO2-delta for NO removal is mainly derived from the synergistic effects of the oxygen vacancies (OVs) and p-n heterojunction. The OVs not only enhance the visible light utilization and boost the separation of electronhole pairs but also improve the adsorption and activation of NO and O-2. Particularly, the p-n heterojunction is beneficial for the interfacial migration of photogenerated charge carriers. Electron spin resonance (ESR) and trapping experiment reveal that the synergistic effects of OVs and p-n heterojunction can induce the generation of more active species. The electrochemical measurements and density-functional theory (DFT) calculations indepth confirm that both p-n heterojunction and OVs can accelerate the interfacial charge transfer, resulting in the deep oxidation of reactants. Therefore, the flower-like beta-Bi2O3/CeO2-delta p-n heterojunction photocatalyst exhibits an advanced photocatalytic activity for deep NO removal and a suppressed NO2 generation. In addition, monitoring the reaction products by in situ Fourier transform infrared spectrum (FTIR) further validates that the main products of nitrates are formed during the photocatalytic process. This work demonstrates a straightforward approach for construction of p-n heterojunction photocatalysts, which can enhance the effective photocatalytic activity and stability for NO removal
Estimates and determinants of soil organic carbon and total nitrogen stocks up to 5 m depth across a long transect on the Loess Plateau of China
No full textPurpose Carbon (C) and nitrogen (N) soil profiles are influenced by several environmental factors. However, the contents and distributions of these elements in deep soils and sediments are largely underestimated. We aimed to estimate the stocks, patterns, and driving factors of deep soil C and N on the Chinese Loess Plateau (CLP) after large-scale ecological restoration projects. Materials and methods Soil organic carbon (SOC) and total nitrogen (TN) contents in different soil layers were measured directly at 86 sites along a regional transect across the CLP. Results and discussion SOC and TN contents ranged from 1.97 to 6.83 g C kg(-1) and 0.24 to 0.72 g N kg(-1), respectively, as the soil depth varied from 0 to 5 m. The mean contents and degrees of variability of SOC and TN decreased with the increasing of soil depth. Based on SOC and TN content patterns, we divided the 0-5-m soil profile into layers of 0-0.1, 0.1-0.4, 0.4-1, and 1-5 m. In the 1-5-m soil layer, approximately 70% of the mean SOC stock (14.97 kg C m(-2)) and 71% of the mean TN stock (1.75 kg N m(-2)) were stored. A partial least square regression model showed satisfactory predictive performance, with R-2 and Q(2) > 0.5 for SOC and TN stocks in the 0.1-0.4-m soil layer. Climatic factors, soil water content (SWC), and field capacity strongly affected SOC and TN stocks in all soil layers. The significance of clay content, SWC, and normalized difference vegetation index varied with soil depth and became the strongest in the 1-5-m soil layer. The highest proportion of SOC and TN stocks for this soil layer were found in grassland and in 450-550 mm rainfall zone. Conclusion Considerable amounts of SOC and TN stocks were stored in the 1-5-m-deep soils. Land-use types and rainfall zones can significantly affect the SOC and TN stocks. This information is helpful for identifying local land uses associated with high SOC and TN stocks and is essential for accurately estimating and predicting regional C and N stocks and cycles in terrestrial ecosystems
Evolution of the dry-wet variations since 1834 CE in the Liiliang Mountains, north China and its relationship with the Asian summer monsoon
No full textUnder the background of global climate change, arid to semi-humid areas are more vulnerable to extreme climate, such as floods and droughts. To better predict and cope with future climate change, more local and regional long-term high-resolution climate reconstructions, hydroclimate in particular, are required. Based on a 174-year regional tree-ring-width chronology, we reconstructed the February-June Standardized Precipitation Evapotranspiration Index (SPEI26) history in the Luliang Mountains, North China (NC). Reconstructed SPEI26 is expected to reflect the dry-wet variation from spring to early summer (STES) of NC with an explained variance of 43.8% for the instrumental record (1951-2007 CE). The reconstruction reveals three comparatively dry (1857-1878, 1919-1929 and 1995-2001 CE) and four comparatively wet (1883-1895, 1934-1944, 1952-1961 and 1980-1984 CE) periods during 1834-2007 CE. Although a drying trend is seen since the 1950s, an advent of wetting since the end of the 1990s is expected. As the driest period in the reconstruction, 1919-1929 CE records the widespread catastrophic 1920s drought in northern China. In addition to the local hydroclimatic signal, the reconstruction also reflects hydroclimatic variation over a large portion of northern China, which is evidented by the comparison with other hydroclimatic records and regional dry-wet index. Strength of the Indian summer monsoon and the East Asian summer monsoon in the previous year play vital roles in the STES dry-wet variations. Moreover, Atlantic Multi-decadal Oscillation index influents the hydroclimate in NC by influencing the Asian summer monsoon system
Parent, alkylated, oxygenated and nitrated polycyclic aromatic hydrocarbons in PM2.5 emitted from residential biomass burning and coal combustion: A novel database of 14 heating scenarios
No full textTo characterize the emissions of polycyclic aromatic hydrocarbons (PAHs) from residential biomass burning and coal combustion in field environments, smoke samples were collected from the combustion of six types of biomass in heated kangs and four types of coal in traditional stoves and semi-gasifier stoves. The emission factors (EFs) of the total PAH were in the range of 84.5-344 mg/kg for biomass burning, with lower EFs for biomass with higher densities, and in the range of 38.0-206 mg/kg for coal combustion, with lower EFs for coals with higher maturity. Moreover, EFs were lower from high-density biomass fuels (wood trunk, 84.5 +/- 11.3 mg/kg) than low-maturity coals (bituminous coal, 206 +/- 16.5 mg/kg). Parent, oxygenated, alkylated, and nitrated PAHs accounted for 81.1%, 12.6%, 6.2%, and 0.1%, respectively, of the total-PAH EFs from biomass burning, and 84.7%, 13.8%, 1.4%, and 0.1%, respectively, of the total-PAH EFs from coal combustion. PAH source profiles differed negligibly between biomass fuels but differed significantly between bituminous coal and anthracite coal fuels. The characteristic species of sources were phenanthrene, 9-fluorenone, and 2-nitrobiphenyl for biomass burning, and were phenanthrene, benzo[ghi]perylene, 1,4-naphthoquinone, and 2-nitrobiphenyl for coal combustion. The ratios of benzo [fluorantheneg benzo [b] fluoranthene + benzo [k]fluoranthene) were 0.40-0.45 for biomass burning and 0.89-0.91 for coal combustion, and these significantly different values constitute unique markers for distinguishing these fuels in source apportionment. Benzo[a]pyrene-equivalent factor emissions were 2.79-11.3 mg/kg for biomass and 7.49-41.9 mg/kg for coal, where parent PAHs contributed 92.0%-95.1% from biomass burning and 98.6%-98.8% from coal combustion. Total-PAH emissions from residential heating were 1552 t across Shaanxi province, to which wheat straw (445 t) in biomass burning and bituminous coal (438 t) in coal combustion were the highest contributors. Results from this study provide crucial knowledge for the source identification of PAHs as well as for the design of abatement strategies against pollutant emissions. (C) 2020 Elsevier Ltd. All rights reserved
Strategies for arsenic pollution control from copper pyrometallurgy based on the study of arsenic sources, emission pathways and speciation characterization in copper flash smelting systems
No full textArsenic in copper flash smelting (FS) systems not only affects the quality of products but also poses significant technological and environmental problems. Based on the assessment of arsenic mass partitioning in the FS system, arsenic elimination in off-gassing and tailings is 22%, and most of the arsenic output (69%) is recycled in the FS system. Circulating arsenic, especially arsenic in recycled dust and slag concentrate, is the key reason for high-arsenic-content feed. Dust-type recycled materials (RMs) contribute much more arsenic to the feed than slag-type RMs. Flash smelting furnace electrostatic precipitator (FSF ESP) dust contributes makese the largest contribution to arsenic among the dust-type RMs of mixed dust, especially trivalent arsenic, followed by FSF and flash converting furnace waste heat boiler (FCF WHB) dust, which contributes pentavalent arsenic. FCF WHB dust exhibits a relatively low arsenic content, consisting mainly of As(V)-O. Slag-type recycled materials contribute As(V)-O to the total feed, and As(III) originates from copper concentrates. Considering the arsenic contribution and environmental risk, reducing the recovery of FSF ESP dust can greatly decrease the arsenic grade of FSF feed and volatile As2O3. As one of the main arsenic sources in feed, FSF slag concentrate should be carefully disposed of if separated from feed materials because of its high arsenic-related environmental risk. In contrast, WHB dust and FCF slag are more suitable as RM due to their high copper content and low arsenic risk. (C) 2020 Elsevier Ltd. All rights reserved
Rill development and its change rate: a field experiment under constant rainfall intensity
No full textRill erosion is a widespread form of soil erosion on loess slope surfaces. The rill formation, evolutionary mechanism, and the quantitative expression of rill erosion dynamic changes in a micro-topographic level are currently lacking, primarily owing to lack of finer-scale measurements. This work presented the rill erosion evolutionary process and their dynamic changes at different slope gradients, (12 degrees, 18 degrees) in a millimeter-scale analysis. We achieved it by constructing an artificial excavation in the field and performed a soil pan with dimensions of 8 m in length and 2 m in width, which were subjected to a constant rainfall intensity of 100 mm h(-1). The multiphase micro-geomorphologic changes during each rainfall phase were monitored using high-resolution terrestrial laser scanner (TLS). We noticed that the larger overland flow in the rill corresponded to more pronounced fluctuations in the cross-section lines of the rill bed. Also, with more the number of rills, the more easily the overland flow was dispersed, which required a larger slope gradient to resume the erosion and fill processes. Erosion rate and fill rate were highly correlated in general, and they increased abruptly at 70-90 degrees. Due to the presence of swelling minerals, the loess surface expanded rapidly after encountering water in the early stage of rainfall. Therefore, the amount and rate of erosion on the slopes were underestimated. Understanding the detailed evolution process of rill erosion from a micro-perspective can provide a valuable reference for the development law of the initial stage of slope erosion in the loess region where erosion is extremely serious
Quantifying soil-respired CO2 on the Chinese Loess Plateau
No full textSoil respiration is one of the dominant fluxes of CO2 from terrestrial ecosystems to the atmosphere. Accurate quantification of soil respiration is essential for robust projection of future climate variation and for reliable estimation of paleoatmospheric CO2 levels using soil carbonates. Soil-respired CO2, which is the most uncertain factor in estimating atmospheric CO2 concentration, has been calculated from modern observations of surface soils and from proxy indicators of paleosols formed during time periods of known atmospheric CO2. However, these estimations provide a wide range of S(z) values from past to present. To directly compare modern observation with past estimation, here we first monitored soil CO2 profiles in a Holocene profile on the western Chinese Loess Plateau (CLP) for two years, providing direct measurements of soil-respired (CO2 )at the depth where carbonate nodules likely formed. We then collected carbonate nodules below last interglacial paleosol (S1) from two N-S-aligned transects across the CLP to back-calculate soil-respired CO2. The mean back-calculated S(z) from S1 carbonate nodules vary from 539 +/- 87 ppm to 848 +/- 170 ppm in the sections on the northwestern and southeastern CLP, respectively. The mean value of directly measured soil-respired CO2 on the western CLP is 572 + 273 ppm before the onset of summer monsoon, consistent with the back-calculated S(z) in northwestern sections. Our results suggest that spatial S(z) variations are mainly controlled by monsoonal precipitation during the summer season on the CLP. To better constrain the high end of S(z), more monitoring work is needed in higher precipitation areas on the southeastern CLP