Institute of Earth Environment
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High-resolution late Pliocene-quaternary magnetostratigraphy of the Yinchuan Basin, NE Tibetan Plateau
No full textThe Yinchuan Basin, one of the most important basins in the area adjacent to the northeastern Tibetan Plateau, contains a continuous sequence of fluvio-lacustrine deposits, which makes it an ideal area to study the in-teractions between the Tibetan Plateau uplift, climate change, and geomorphological evolution. Here, a 1200-m -deep drill core (YNZK01) is described with an average recovery rate of 96% in the depo-center of the Yinchuan Basin to establish a high-resolution palaeoenvironmental and tectonic reconstruction. Stepwise alternating-field demagnetization results showed a stable and high-qualified remanent magnetization of the samples. The polarity sequences consisted of 8 normal and 8 reverse zones that correlate well with the geomagnetic polarity timescale. Magnetostratigraphic results date the entire YNZK01 core from 3.927 Ma to the present. The B/M boundary (0.781 Ma) is at a depth of 246.4 m while the M/G boundary (2.581 Ma) is at a depth of 863.4 m. The G/Gi boundary (3.596 Ma) is identified at 1117.8 m and the bottom of the core was extrapolated to 3.927 Ma (1201 m) with an average sedimentation rate of 863.4-1117.8 m. This high-resolution magnetostratigraphy record pro -vides a baseline chronological framework for further research and publications on the tectonic, paleoclimatic, and paleoenvironmental proxy data of the YNZK01 core in the Yinchuan Basin, NE Tibetan Plateau
Novel investigation of pyrolysis mechanisms and kinetics for functional groups in biomass matrix
No full textBiomass, as a renewable and sustainable energy resource, can be converted into environmentally friendly and practically valuable biofuels and chemical materials via pyrolysis. However, the process optimization and pyrolysis efficiency are restricted by the limited perception of the complicated mechanisms and kinetics for biomass pyrolysis. Here, to establish an in-depth mechanism model for biomass pyrolysis, we presented a novel investigation for the thermal evolutions and pyrolysis kinetics of the functional groups in peanut shell matrix by using in-situ Fourier transform infrared spectrometry (in-situ FTIR) and thermogravimetric analysis-Fourier transform infrared spectrometry-mass spectrometry (TG-FTIR-MS). The in-situ FTIR spectrum deconvolution for the solid matrix was innovatively introduced to identify and quantify the real-time evolution and thermal dynamics of the functional groups during peanut shell pyrolysis. The result for the first time proposed that the pyrolysis mechanisms of total OH at 20-380 degrees C, aliphatic C-H-n groups at 20-500 degrees C, C=O groups at 260-500 degrees C, and C-O groups at 300-500 degrees C were dominant by diffusion and order-based chemical reactions. The TG-FTIR-MS analysis was conducted for the online monitoring of the released volatiles and gases, the amounts of which were in the sequence of C=O > CO2 > aliphatic C-O-(H) > C-O-(C) in esters > aromatics > H2O > phenolic hydroxyl > aliphatic hydrocarbons > CO. The study established a novel methodology to evaluate the biomass pyrolysis mechanisms at the molecular level, which provided valuable information for developing advanced pyrolysis techniques on a large scale for sustainable ecosystem
Oxygen vacancy engineering of photocatalytic nanomaterials for enrichment, activation, and efficient removal of nitrogen oxides with high selectivity: a review
No full textAir pollution by trace levels of nitric oxide (NO) pollution is threatening human health by causing acid rain and haze pollution through photochemical reactions. Here, we review photocatalytic technologies that use oxygen vacancy engineering-mediated nanomaterials for the control of air pollutants such as NO and nitrogen dioxide. We present oxygen vacancy parameters and reactor regulation mechanisms. We explain the functions of oxygen vacancies in the adsorption and enrichment processes of NO on the photocatalyst surface. We highlight the relationship between oxygen vacancies and O-2 activation in photocatalytic reactions. The mechanisms ruling selectivity in NO photodegradation, and the suppression of photocatalyst deactivation are discussed.
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Late Holocene hydroclimatic changes inferred from a karst peat archive in the western Guizhou Plateau, SW China
No full textThe paleoenvironmental implications of Ca-related indices of peat from karst regions are poorly understood. In this study, we analyze a 450-cm peat core drilled from a sub-alpine karst mountain in the western Guizhou Plateau, SW China. This core is analyzed for carbonate contents and loss on ignition (LOI). High-resolution X-ray fluorescence (XRF) core scanning was also performed to see the variation of chemical compositions. Based on these measurements and 12 accelerator mass spectrometry (AMS)C-14 dates, we reconstructed the history of hydroclimatic shifts in SW China and explored the significance of Ca-related indices. The reconstructed hydro climatic conditions were consistent with the stalagmite, lacustrine sediment, and peat records from the regions controlled by the Indian monsoon. Abrupt decreases in precipitation and temperature were clearly shown during the 4.2 ka and Little Ice Age (LIA) cold events. High carbonate contents in the Yejiping peat during the Medieval Warm Period (MWP) were linked to a warm and humid climate. Additionally, wavelet analysis shows that variations in Ca content have 500, 125, 103, 80, 58, 43, 20, and 12-a quasi-periods, which correspond to the Gleissberg, Pacific Decadal Oscillation (PDO), and Schwabe cycles. Our results highlight the importance of Ca related indices in peat deposits from karst depressions and provide a detailed description of the MWP and the LIA
<p>Deep root information "hidden in the dark": A case study on the 21-m soil profile of Robinia pseudoacacia in the critical zone of the Chinese loess Plateau & nbsp;</p>
No full textDeep roots can uptake deep soil water to support plant growth and mitigate climate change in water-limited ecosystems. Few studies have been conducted on the deep root characteristics in the soil profile as limited field data are available. To explore the relationship between the deep root characteristics, depth, and soil water status, we obtained the distribution pattern of deep roots and soil water content along a 21-m soil profile (n = 22) in a mature Robinia pseudoacacia plantation. The maximum rooting depth, mean root biomass, and mean depths corresponding to 50% and 90% of the total root biomass of 17-year-old R. pseudoacacia trees were > 20 m, 0.083 +/- 0.029 g.cm(-2), 1.17 +/-& nbsp; 1.74, and 6.15 +/-& nbsp; 3.98 m, respectively. We established an exponential power model to fit the relationship between the deep root biomass and soil depth, which had a higher goodness-of-fit than the typical exponential model, logistic model, and piecewise linear model. The root morphological characteristics along the 21-m vertical profile rapidly decreased with depth in the 0-1-m layer, and then stabilized, while the specific root length (SRL) and specific root area (SRA) increased with depth. The relationships between the SRL, SRA, and soil water content in the dried soil layers with roots (SWC-DSL) were significantly positive (both p < 0.01), while those between average root diameter density and SWC-DSL were significantly negative (p < 0.001), suggesting that roots increased their length rather than diameter to acquire water resources with relatively low carbon investment. The soil depth and soil water availability co-controlled root biomass and root morphological characteristics. Our findings highlight the importance and complexity of deep roots and their morphological characteristics, which are fundamental for forest models and management to maintain sustainable development between soil water and root water uptake.& nbsp
Emission characteristics and formation mechanisms of PM2.5 and gases from different geological maturities coals combustion
No full textTo evaluate the influence of geological maturity on coal combustion pollutant emissions, six chunk coals and corresponding briquettes (volatile matter [VM] content from 8.0% to 39.9%) were selected for simulated residential combustion in a carefully designed chamber, and the formation mechanism involved was investigated. VM was revealed to have a nonlinear effect on the emission factors (EFs) of particulate matter with an aerodynamic diameter of <2.5 mu m (PM2.5), polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC), and organic carbon (OC), with the highest EFs observed in VM of 15.8% and 26.8%. Coal tar yield and air-supply from VM combustion in its initial stage was found to be a key factor influencing PM2.5 and PAH emissions when compared with the char combustion and burnout stages. The highest PM2.5 and PAH EFs were observed in coal with 15.8% VM. Additionally, significant amounts of hydrogen cyanide (HCN) were detected at stage 1 and were released as volatile-N through the pyrolysis of coal-N. N2O and NOx were also emitted through homogeneous gas-phase HCN reactions. However, only a small proportion of NOx was produced, indicating that the contribution of VM to HCN and N2O emissions is greater than that of NOx. In the char reaction stage (stage 2), char-N reacted with O-2 to form large amounts of NO, and the reaction length of the entire coal combustion process exhibited a positive relationship with coal maturity (correlation coefficient 0.69, p < 0.05), suggesting that the contribution of NO from char-N to overall NO emissions increased with the coal's geological maturity due to the increase in coal-N retention in char. Furthermore, coal briquetting was found to decrease the EFs of pollutants, which may be explained by an increase in MCE (modified combustion efficiency) and the conversion from coal tar to carbon and hydrogen. This study elucidated the effects of geological maturity on pollutant emissions from coal combustion and examined relevant underlying mechanism. These data can serve as the foundation for a clean coal project in China or other counties concerned with coal combustion emissions
Chromophoric dissolved organic carbon cycle and its molecular compositions and optical properties in precipitation in the Guanzhong basin, China
No full textThe investigation of water-soluble organic carbon (WSOC), which is important in the biogeochemical cycle of precipitation, can provide a comprehensive view of chromophores within the atmospheric boundary layer. In this work, the optical properties and molecular characteristics of WSOC in precipitation over the Guanzhong Basin (GB) of North China were investigated using ultraviolet-visible (UV-vis) absorption and excitation-emission matrix (EEM) fluorescence spectra, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with electrospray ionization (ESI). Furthermore, sources and wet deposition of WSOC were estimated using in-situ measurements and modeling. The light-absorption by WSOC at 250-300 nm (UV region) and 400-550 nm (visible region) was 64.17% and 15.36% relative to the estimated total light-absorption, respectively. Parallel factor (PARAFAC) analysis revealed three types of fluorophores in WSOC at Xi'an (XN), including two humic-like substances (HULIS) and one protein-like substance (PRLIS), with HULIS accounting for 79% of total fluorescence intensity. FT-ICR MS analysis revealed that CHO and CHON were the most abundant components of WSOC at XN, each containing a variety of lignins, protein/amino sugars, and lipids. Moreover, the positive matrix factorization (PMF) model identified the contributions from three main sources (secondary precursors and aerosols, and coal combustion) of WSOC in precipitation at XN. The annual wet deposition flux of WSOC in precipitation at XN was estimated as about 0.63 g C m(-2) yr(-1), lower than that at other polluted cities. These findings add to our understanding of chromophoric dissolved organic carbon budgets, which is critical for accurately assessing the global carbon cycle
Tree-ring-based drought variability in northern China over the past three centuries
No full textDroughts are the most frequent natural disaster in regions at the margins of the East Asian summer monsoon (EASM), which pose threats to agriculture, the economy, and human lives. However, the limitations of only approximately 60 years of meteorological observations hamper our understanding of the characteristics and mechanisms of local hydroclimate. Trees growing in the marginal region of the EASM are usually sensitive to moisture variations and have played important roles in past hydroclimatic reconstructions. Here, a 303-year tree-ring-width chronology of Pinus tabulaeformis from Mt. Lama, which is located in the junction of the Liaoning Province and Inner Mongolia, China, was used to reconstruct the May-August Palmer drought severity index (PDSI) in the marginal region of the EASM. The transfer function explains 48.0% (or 47.2% after adjusting for the loss of the degrees of freedom) of the variance over the calibration period from 1946 to 2012. A spatial correlation analysis demonstrates that our PDSI reconstruction can represent the drought variability on the northernmost margin of the EASM. The winter Asian polar vortex area index showed a delayed impact on the summer EASM precipitation in the following year
Concentration, optical characteristics, and emission factors of brown carbon emitted by on-road vehicles
No full textAtmospheric brown carbon (BrC) is a light-absorbing component that affects radiative forcing; however, this effect requires further clarification, particularly with respect to BrC emission sources, chromophores, and optical properties. In the present study, the concentrations, optical properties, and emission factors of organic carbon (OC), water-soluble OC (WSOC), and humic-like substances (HULIS) in fine particulate matter (PM2.5) emitted from vehicles in three road tunnels ( the Wucun, Xianyue, and Wenxing tunnels in Xiamen, China) were investigated. The mass concentrations and light absorption of OC, WSOC, and HULLS were higher at the exits of each tunnel than at entrances, demonstrating that vehicle emissions were a BrC source. At each tunnel's exit, the average light absorption contributed by HULIS-BrC to water-soluble BrC (WS-BrC) and total BrC at 365 nm was higher than the corresponding carbon mass concentration contributed by HULIS (HULIS-C) to WSOC and OC, indicating that the chromophores of HULIS emitted from vehicles had a disproportionately high effect on the light absorption characteristics of BrC. The emission factors (ER) of HUUS-C and WSOC mass concentrations were highest at the Xianyue tunnel; however, the EFs of HULIS-BrC and WS-BrC light absorption were highest at the Wenxing tunnel, indicating that the chromophore composition of BrC was different among the tunnels and that the mass concentration EFs did not correspond directly to the light absorption EFs. (C) 2021 Elsevier B.V. All rights reserved
Exceptional terrestrial warmth around 4200-2800 years ago in Northwest China
No full textOne of the Holocene abrupt events around 4200 years ago, lasting for -200 years, is thought to have caused cultural disruptions, yet terrestrial climatic status right after the cold/dry event remains poorly defined and is often presumed that a generally cool condition prevailed during the Bronze Age (4000-2200 years ago). Here we report an alkenone-based summer temperature record over the past -12,000 years, in addition to two updated alkenone records, from Northwest China, providing new insights into the climatic status right after the event. Our results indicate that exceptional terrestrial warmth, up to -6 degrees C, occurred around 4200-2800 years ago during the Bronze Age, superimposed on the long-term Holocene cooling trend. The exceptional warmth in Northwest China, together with other climate anomalies elsewhere, suggests an unusual large-scale climatic reorganization at 4200-2800 years ago when solar activity remained high, with important implications to the climate background for cultural developments during the Bronze Age. (c) 2021 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved