Institute of Earth Environment
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Maximizing the Formation of Reactive Oxygen Species for Deep Oxidation of NO via Manipulating the Oxygen-Vacancy Defect Position on (BiO)(2)CO3
No full textConstructing oxygen vacancies (OVs) in metaloxide semiconductors is an effective and simple way to enhance the photocatalytic performance via promoting the utilization of solar light and boosting the formation of surface reactive oxygen species (ROS). The presence of different oxygen atoms in the same crystal structure can possibly lead to the formation of different types of OVs with distinct physicochemical and optoelectronic properties. Particularly, the two different crystallographic positions of oxygen atoms in the [BiO](2)(2+) layer of (BiO)(2)CO3 (BOC) allow the construction of two types of OVs (OVs1 and OVs2). In this work, OVs1-BOC and OVs2-BOC are synthesized via introducing the OVs1 and OVs2 on the surface of the BOC. The influence of OVs1 and OVs2 on the generation of ROS in the BOC is demonstrated based on theoretical and experimental studies by analyzing the separation and redox potentials of photogenerated charge carriers, absorption surface adsorbates (H2O and O-2), and reaction active energy. The photocatalytic performance is evaluated by photo-oxidative nitric oxide (NO) removal efficiency under visible light irradiation. The OVsl-BOC and OVs2-BOC exhibit 50.0 and 41.6% photo-oxidative NO removal efficiencies, while generating 15.6 and 16.54 ppb NO2, respectively. The in situ Fourier transform infrared spectroscopy and estimated NO conversion pathway reveal the photo-oxidative NO removal mechanism and suppression of NO2 formation on the surfaces of OVs1-BOC and OVs2-BOC. This work demonstrates a straightforward approach for enhancing the photo-oxidative NO removal via manipulating the OV defect position in semiconductors
Quantification of solid fuel combustion and aqueous chemistry contributions to secondary organic aerosol during wintertime haze events in Beijing
No full textIn recent years, intense haze events in megacities such as Beijing have received significant attention. Although secondary organic aerosol (SOA) has been identified as a major contributor to such events, knowledge of its sources and formation mechanisms remains uncertain. We investigate this question through the first field deployment of the extractive electrospray ionisation time-of-flight mass spectrometer (EESI-TOF) in Beijing, together with an Aerodyne long-time-of-flight aerosol mass spectrometer (L-TOF AMS). Measurements were performed during autumn and winter 2017, capturing the transition from non-heating to heating seasons. Source apportionment resolved four factors related to primary organic aerosols (traffic, cooking, biomass burning, and coal combustion), as well as four related to SOA. Of the SOA factors, two were related to solid fuel combustion (SFC), one to SOA generated from aqueous chemistry, and one to mixed/indeterminate sources. The SFC factors were identified from spectral signatures corresponding to aromatic oxidation products, while the aqueous SOA factor was characterised by signatures of small organic acids and diacids and unusually low CO+/CO2+ fragment ratios measured by the AMS. Solid fuel combustion was the dominant source of SOA during the heating season. However, a comparably intense haze event was also observed in the non-heating season and was dominated by the aqueous SOA factor. During this event, aqueous chemistry was promoted by the combination of high relative humidity and air masses passing over high-NOx regions to the south and east of Beijing, leading to high particulate nitrate. The resulting high liquid water content was highly correlated with the concentration of the aqueous SOA factor. These results highlight the strong compositional variability between different haze events, indicating the need to consider multiple formation pathways and precursor sources to describe SOA during intense haze events in Beijing
New chronology of the Chinese loess-paleosol sequence by leaf wax delta D records during the past 800 k.y.
No full textThe Chinese loess-paleosol sequences provide important archives for studying paleoenvironmental changes. However, the lack of independent and accurate time scales hinders the study between loess and other records. Asian stalagmite delta O-18 records indicate synchronous patterns of paleoprecipitation delta O-18 over large geographic regions. The record of hydrogen isotopic composition of plant wax (delta D-wax) in Chinese loess is also controlled by rainwater delta D. Both share a common origin. The linear relationship between rainfall delta O-18 and delta D variance provides the basis to tie together chronologies of the same climate event in different records. Here, we show a new loess chronology by correlating chronologies of marker boundaries of the prominent climate chronozones in stalagmite delta O-18 and summer insolation to the equivalent climate stratigraphy in the loess delta D-wax sequence. We first developed and tested this novel methodology with data since the last interglacial on a millennial scale, and then applied this approach to the loess delta D-wax sequence for the past 800 k.y. to improve the traditional chronology based on magnetic susceptibility and grain size. The new delta D-wax time series provides not only an improved chronology for studying paleoclimate changes during interglacial intervals, it also represents a unique database with which to better understand the links between the Asian monsoon changes in the Chinese loess and other global climate events, especially for the periods prior to 640 ka, for which stalagmite records are not available
Late Quaternary glacial history of the Altyn Tagh Range, northern Tibetan Plateau
No full textQuantifying the timing and extent of late Quaternary glaciations across the Tibetan Plateau (TP) is critical to understanding regional and global climate changes. Despite significant advancements in our knowledge of glacial histories of the TP over the past several decades, chronological constraints are still lacking for the high glaciated mountain ranges on the northern TP, including the Altyn Tagh Range. In this study, we provide thirty-two new Be-10 exposure-ages to construct a late Quaternary glacial history of the Altyn Tagh Range at the Altyn "Pass" and Akato Tagh. The dating results from Altyn "Pass" indicate that glacier might have fully melted out of this area after Marine Isotope Stage 3 (MIS 3). The tentatively-defined minimum moraine ages north of Akato Tagh show that four glacial culminations possibly occurred during MIS 5, MIS 4, MIS 3 or 2, and the late Holocene. These dating results, together with the compiled exposure-ages from Sulamu Tagh, imply that the last glacial glacier fluctuations along the Altyn Tagh Range were likely driven by several factors: North Atlantic climate oscillations, northern hemispheric high-latitude summer solar insolation, atmospheric CO2 concentrations, and geometry of glacier catchment. The progressive reduction in glacier extent during the last glacial is likely associated with available precipitation, controlled by the mid-latitude westerlies
Stable Isotopes Reveal Water Vapor Sources of Precipitation over the Jiaolai Plain, Shandong Peninsula, China
No full textA prerequisite for using isotopic techniques to study the regional water cycle of a mountainous area is to examine the stable isotopic composition of precipitation. These findings are of great significance for an in-depth understanding of water cycle processes. In this study, each precipitation event was sampled and used to investigate the characteristics of stable hydrogen and oxygen isotopes in precipitation over the Jiaolai Plain and its surrounding areas. NCEP/NCAR data was used for the wind speed and direction, relative humidity, and precipitable amount in the study area during the sampling period. The water vapor sources of the precipitation over the plain were revealed through a comparative analysis of seasonal variations in precipitation isotopes between Global Network of Isotopes in Precipitation stations located along different vapor transport paths. The results showed that the local meteoric water line was delta H-2 = 6.38 delta O-18 + 0.72, with a gradient of less than 8. This indicates that the precipitation process was affected by non-equilibrium evaporation occurring when the drops fell below the cloud base. Temperature and amount effects were observed in the delta O-18 of the precipitation, although the altitude effect was not significant. The water vapor source of the precipitation was predominantly controlled by the East Asian Monsoon from June to September, with the primary source being evaporation from the adjacent Pacific Ocean. The plain was controlled by the Westerlies from October through May, with the predominant vapor source being local evaporation. Water vapor from the polar region had a minimal impact. These findings can serve as the basis for studying surface water-groundwater-seawater transformations
Properties of cement mortar containing recycled glass and rice husk ash
No full textUsing recycled glass (RG) to replace river sand in the production of cement-based materials saves the increasingly depleting natural sand resources. Previous studies have shown that the smooth surface and reactive silica of RG adversely affected its bonding with the cement paste and thereby caused a potential alkali-silica-reaction (ASR). This study used rice husk ash (RHA) as an eco-friendly mineral admixture to ameliorate the properties of the RG incorporated mortar. A fixed replacement of 50% RG was used to replace sand, while varying proportions (10%, 20% and 30%) of RHA were adopted to replace cement. For comparison, a mixture containing only sand and cement was used as the reference sample. The flexural and compressive strength, water absorption, ASR expansion, and rapid chloride mitigation (RCM) of the hardened samples were evaluated. In addition, SEM, XRD, and TG analysis were employed to analyze the microstructures and chemical compositions of different samples. The results showed that incorporating RG as a river sand replacement in cement mortar reduced flexural and compressive strength and increased water absorption and chloride ion penetration. Moreover, the ASR expansion value (0.34%) was beyond the permissible limit (0.1) indicated by the ASTM C1260. The addition of RHA improved the mechanical properties and durability of the cement mortar at a later curing age as a result of the RHA-induced pozzolanic reaction and micro-filler effect. By converting portlandite (CH) derived from cement hydration into secondary C-S-H, the use of RHA greatly reduced the porosity (augmenting the compressive and flexural strength) and concurrently suppressed the RG-induced ASR expansion. The results of XRD, SEM and TG analysis corresponded well with the macro-property analysis and helped to elucidate the underlying mechanisms of the RHA-induced beneficial effects. Findings from this study provide new insights into the potential use of eco-friendly RHA in addressing the mechanical and durability problems associated with the use of RG as aggregate in cementitious materials. (c) 2021 Elsevier Ltd. All rights reserved
Geochemical Anomaly Characteristics of Cd in Soils around Abandoned Lime Mines: Evidence from Multiple Technical Methods
No full textLime mines are a potential source of pollution, and the surrounding soil environment is generally at threat, especially in abandoned lime mines. This paper focuses on the study area in eastern Anhui, attempting to analyze whether Cd enrichment is related to abandoned mines. On the basis of geological investigation, this study systematically used XRD, XRF, GTS and universal Kriging interpolation to determine the distribution law of Cd in the study area, and evaluated the potential ecological risk of Cd. The results showed that the main mineral types of soil samples of red clastic rock soil parent material (RdcPm) and soil samples of carbonate soil parent material (CPm) were not completely the same. Correlation analysis showed that CaO, MgO and Cd were positively correlated with the CPm. Human activities led to the accumulation of Cd in the study area. High Cd was mainly concentrated in the northwest of the study area, which was correlated with abandoned mines and soil parent materials. The study area was dominated by slight potential risks, although some areas had medium potential risks and high potential risks. All potential high risks were in the CPm field. This study provides a scientific basis for the comprehensive utilization and development planning of soil in the study area
Re-utilization of Chinese medicinal herbal residues improved soil fertility and maintained maize yield under chemical fertilizer reduction
No full textExcessive utilization of chemical fertilizers (CF) is not a sustainable agricultural development strategy due to adverse effects on soil health. In contrast, a combination of organic and mineral fertilizers has a positive effect on both soil health and productivity. Chinese medicinal herbal residues (CMHR) is the plant material wastes remaining after drug extraction but has not been extensively used as fertilizer. We evaluated application of CMHR to maize fields over 3 consecutive growing seasons in the presence and absence of standard CF to assess improvements in soil fertility, maize yields and sustainable development. CMHR fertilization increased soil organic matter and total N and K when mixed with chemical fertilizer at 50 and 75% the standard application rate. Soil organic matter increased by 27.0-51.4% and available -N, -P and -K levels and grain yields as well as N and P use efficiency in the presence of CMHR mixes were similar to levels obtained with chemical fertilizer only. These increases in production were due to increased leaf areas, photosynthetic rates, grain number and 1000-grain weights. The addition of CMHR to fields posed a slightly risk of toxic-metal pollution. Overall, we found that (1) CMHR can be used as an effective organic fertilizer and replace up to 50% of the amount of chemical fertilizer normally applied to fields without hampering maize grain yields and (2) CMHR application to agricultural fields is an effective recycling strategy and nutrient management practice to improve soil fertility under CF usage reduction
Seasonal/Interannual Variation and Controlling Factors for Oxygen and Carbon Isotopes of Ostracod Shells Collected From a Time-Series Sediment Trap in Lake Qinghai
No full textBecause the shell substance of an ostracod is derived entirely from the water body where it lives, its chemical compositions are sensitive to aquatic environment and thus have been used to reconstruct past climatic and environmental changes. However, there is controversy about the controlling factors for the different compositions of ostracod shells from various water bodies. In this study, seasonal and interannual variations in daily flux and stable oxygen-carbon isotopic compositions (518O, 513C) for two species of ostracod shells (Limnocythere inopinata and Eucypris mareotica) and their controlling factors are discussed, based on ostracod shell samples collected from a time-series sediment trap from July 2010 through September 2012 and from surface sediments in Lake Qinghai, which were correlated with the state-of-the-art sensing data of the lake water. The results show that the daily flux of L. inopinata shells is an order of magnitude higher than that of E. mareotica. The 518O and 513C of both L. inopinata and E. mareotica shells have distinctly interannual and seasonal variations, with species differences. Interannual differences of 518O for the two species of ostracod shells directly reflect the systematic differences of the summer water temperature between 2010 and 2012. We propose that seasonal variations of both 518O and 513C for the two species are affected by the precipitation of authigenic carbonates in microenvironment induced by high water temperature in summers, highlighting their environmental implications in Lake Qinghai
Important contribution of N2O5 hydrolysis to the daytime nitrate in Xi' an, China during haze periods: Isotopic analysis and WRF-Chem model simulation
No full textNitrate, as one of the major components of tropospheric aerosols, plays a crucial role in winter haze formation. While, the formation mechanism of the high production of nitrate in Chinese megacities is still not fully understood. To quantify the contributions of major formation pathways to nitrate, airborne particles in Xi'an, inland China during the winter of 2017 were measured and analyzed for the water-soluble ions and stable nitrogen/oxygen isotope compositions of nitrate in PM2.5, followed by a WRF-Chem model simulation. The oxygen isotopic results indicated that N2O5 hydrolysis was an important formation pathway for the daytime nitrate in the haze episodes. The model simulation further revealed that N2O5 hydrolysis contribution increased from 8.2% to 20.5% of the total nitrate over 14:00-16:00 p.m., clearly showing that N2O5 formation followed by a heterogeneous hydrolysis to nitrate can effectively proceed in daytime under the abundantly co-existing O-3, NO2 and NH3 conditions