Institute of Earth Environment
Institutional Repository of Institute of Earth Environment, CASNot a member yet
7120 research outputs found
Sort by
Early Oligocene-Late Miocene Wildfire History in the Northern Tibetan Plateau and Links to Temperature-Driven Precipitation Changes
No full textLate Cenozoic wildfire evolution in Inner Asia has been attributed to both ice-volume modulating precipitation changes and surface uplift of the Tibetan Plateau. Whether this is the case or not requires additional research and wildfire records from older periods. In this study, 251 microcharcoal samples from the Huatugou section in the western Qaidam Basin are used to reconstruct the early Oligocene-middle Miocene wildfire history of the northern Tibetan Plateau. The results show that wildfires remained relatively frequent before similar to 26 Ma, then reduced gradually until similar to 14 Ma, and finally increased slightly but still at low level between 14 and 12 Ma. The wildfire variations can be correlated to the steppe-based dryness changes, and both of which are coincident with global temperature changes. We infer that mean annual temperature might have played a dominant role in controlling wildfire frequencies in the northern Tibetan Plateau through modulating atmospheric moisture content. This conclusion is in line with previous studies including microcharcoal-based wildfire records of 18-5 Ma successions from the Qaidam Basin as well as soot-based wildfire records from Quaternary glacial-interglacial cycles of the Chinese Loess Plateau
Holocene climate and soil water balance in Baoji Region of Southern Loess Plateau
No full textIn this paper, changes in the Holocene climate, soil water and soil resources in Southern Loess Plateau are studied based on field investigation, grain size and chemical analysis. The purpose is to reveal the impact of the Holocene environmental change on soil water and human activities. The study shows that the mid-Holocene paleosol S0 in Baoji Region had a CaCO3 content close to 0, was enriched with Fe2O3, Al2O3, was of homogenous dense silty microstructure containing red argillans and had moderate chemical weathering. This shows that the paleosol is luvisol. The mean annual precipitation was about 800 mm at that time. The late-Holocene loess had a high CaCO3 content, low Fe2O3 and Al2O3 content and of pore-developed crumb microstructure, indicating that the climate was cold and dry. The migration depth of CaCO3 and Sr in the mid-Holocene paleosol indicates that the distribution depth of gravity water in the soil at that time reached 1.8 m, and the water content in the soil above 1.8 m during the vegetation growing season was higher than 20%. This made it suitable for the development of forest vegetation. The migration depth of CaCO3 in the Holocene loess was small and the water content in the layers of loess during rainy season was generally lower than 12%; thus, it was not suitable for the development of forest vegetation. In the mid-Holocene soil, water intake was greater than water consumption and soil water was positive balance. Moreover, trace elements, organic matters, water holding capacity and water content in S0 were higher than those in the early-Holocene and late-Holocene loess, which facilitated agricultural production and human activities. In fact, it is also the primary reason that the mid-Holocene village sites are significantly larger in quantity and greater in scale than the early-Holocene and late-Holocene village sites
Determination of the optimized late Pleistocene chronology of a lacustrine sedimentary core from the Heqing Basin by geomagnetic paleointensity and its paleoclimate significance
No full textLong and continuous lacustrine sedimentary sequences from SW China faithfully recorded the evolution of the Indian summer monsoon (ISM). However, the limited dating range (< 50 ka) of C-14 dating has restricted high resolution research on the last glacial cycle.We presented a relative paleointensity (RPI) record from a lacustrine sedimentary core from the Heqing Basin to optimize its AMS C-14 chronology. Detailed rock magnetic analyses indicated that SD and vortex state magnetite (and/or maghemite) was the dominant magnetic mineral of lacustrine sediments. Moderate variations in concentration-dependent (SIRM, ARM) and grain-size-dependent (ARM/SIRM) parameters satisfied the criteria for the RPI studies. Consequently, we determined the RPI by NRM20-40 mT/SIRM20-40 mT, where NRM20-40 mT denotes the NRM after demagnetization between 20 and 40 mT. Using 6 AMS C-14 dates younger than 40 ka BP as constraints, 7 age control points were determined by correlating the lows in the RPI record with those of the target paleointensity stacks PISO-1500. We established a reliable chronological framework of the upper 11.1 m of the HQ drill core by binomial fitting based on the 7 RPI age control points and the climatic transition termination II. The consistent variations in our RPI curve and other global target paleointensity curves indicated that the optimized chronology was reliable.In our optimized chronology, the visible precession cycle in ARM/SIRM indicated that the ISM was a direct response to solar insolation during the last glacial cycle. The strong ISM suggested by the high content of Mesic conifers and tropical and subtropical trees during MIS 3 shifted to MIS 5a. Thus, the "MIS 3 Mega-paleolake " hypothesis in China, which was mainly deduced by the C-14 age model, was challenged
Determination of the optimized late Pleistocene chronology of a lacustrine sedimentary core from the Heqing Basin by geomagnetic paleointensity and its paleoclimate significance
No full textLong and continuous lacustrine sedimentary sequences from SW China faithfully recorded the evolution of the Indian summer monsoon (ISM). However, the limited dating range (< 50 ka) of C-14 dating has restricted high resolution research on the last glacial cycle.We presented a relative paleointensity (RPI) record from a lacustrine sedimentary core from the Heqing Basin to optimize its AMS C-14 chronology. Detailed rock magnetic analyses indicated that SD and vortex state magnetite (and/or maghemite) was the dominant magnetic mineral of lacustrine sediments. Moderate variations in concentration-dependent (SIRM, ARM) and grain-size-dependent (ARM/SIRM) parameters satisfied the criteria for the RPI studies. Consequently, we determined the RPI by NRM20-40 mT/SIRM20-40 mT, where NRM20-40 mT denotes the NRM after demagnetization between 20 and 40 mT. Using 6 AMS C-14 dates younger than 40 ka BP as constraints, 7 age control points were determined by correlating the lows in the RPI record with those of the target paleointensity stacks PISO-1500. We established a reliable chronological framework of the upper 11.1 m of the HQ drill core by binomial fitting based on the 7 RPI age control points and the climatic transition termination II. The consistent variations in our RPI curve and other global target paleointensity curves indicated that the optimized chronology was reliable.In our optimized chronology, the visible precession cycle in ARM/SIRM indicated that the ISM was a direct response to solar insolation during the last glacial cycle. The strong ISM suggested by the high content of Mesic conifers and tropical and subtropical trees during MIS 3 shifted to MIS 5a. Thus, the "MIS 3 Mega-paleolake " hypothesis in China, which was mainly deduced by the C-14 age model, was challenged
A critical review on plasma-catalytic removal of VOCs: Catalyst development, process parameters and synergetic reaction mechanism
No full textIt is urgent to control the emission of volatile organic compounds (VOCs) due to their harmful effects on the environment and human health. A hybrid system integrating non-thermal-plasma and catalysis is regarded as one of the most promising technologies for VOCs removal due to their high VOCs removal efficiency, product selectivity and energy efficiency. This review systematically documents the main findings and improvements of VOCs removal using plasma-catalysis technology in recent 10 years. To better understand the fundamental relation between different aspects of this research field, this review mainly addresses the catalyst development, key influential factors, generation of by-products and reaction mechanism of VOCs decomposition in the plasma-catalysis process. Also, a comparison of the performance in various VOCs removal processes is provided. Particular emphasis is given to the importance of the selected catalyst and the synergy of plasma and catalyst in the VOCs removal in the hybrid system, which can be used as a reference point for future studies in this field
Polycyclic aromatic hydrocarbons from cooking emissions
No full textAir pollution studies have often overlooked the contribution from cooking to the particle-bound polycyclic aromatic hydrocarbons (PAHs) in the ambient environment, despite cooking emissions have been identified as an important source of organic aerosol in most urban areas, known as the cooking-like organic aerosol factor (i.e., COA). In this study, a Long-Time-of-Flight (LToF) soot particle aerosol mass spectrometer (SP-AMS) was deployed to evaluate the impact of cooking emissions on outdoor particle-bound PAHs levels during a summer campaign in 2019 in Xi'an China. Combined with the robust receptor model, cooking emission was found to be the major source of ambient PAHs, on average, accounting for 90% of PAHs, 9 times higher than traffic (10%). The ambient cooking PAH profile was well correlated (r2 of 0.87) with that for frying oil fume, suggesting cooking oil was the major source of PAHs instead of the food being cooked. We further evaluated the health risk associated with the cooking PAHs and estimated the cooking PAH levels in some of the major cities in the world where COA factor has been reported. The results show the particle-bound PAHs from cooking can be an important source of ambient PAHs in most Chinese cities. The findings from this study hold important implications for public health and are informing for policymakers
Altitudinal difference of growth-climate response models in the north subtropical forests of China
No full textAltitudinal difference increases the complexity of the response of tree growth to climate change in the mountainous areas, and may change the carbon sequestration capacity of forests under the ongoing warming climate. In this work, four tree-ring width chronologies from Pinus henryi Mast. growing at different altitudes of Shiyan, the northern subtropical China were developed. Results of Pearson correlation analysis, factor analysis and redundancy analysis indicate that tree growth-climate response models can be divided into two types according to the altitudinal gradient: the high-altitude model, represented by SWDH and WDSH above 1330 m a.s.l., and the low-altitude model, represented by WDSL and DDZL less than 1070 m a.s.l. The biggest difference between the two models is that tree growth at the low altitudes shows significantly negative response to temperature in the previous September-December and current April-May, and positive response to moisture conditions from the previous September to current May, April-May in particular; while the high-altitude ones show consistently positive responses to temperature in current February-April, but no significant response to seasonal moisture condition. The existence of a temperature-related altitudinal threshold between 1070 m a.s.l. to 1330 m a.s.l. may change the hydro-thermal combination models above and below the threshold, thus lead to the change of climatic response models along altitude gradient. 30-yr moving correlation analysis reveals that the relationships between tree growth and the limiting climatic factors present evident altitudinal difference: gradually strengthened at the high altitudes but weakened at the low altitudes. It is distinct that water availability and demand are critical for the growth of low-altitude trees, and high-altitude trees show a stronger positive response to climate warming, therefore could be an important carbon sink in the future. In addition, future forest management should focus on the low altitudes and formulate effective protection strategies
Nitrous acid emission from soil bacteria and related environmental effect over the North China Plain
No full textSoil bacteria could be one of the important sources for ambient HONO. However, the HONO emission from soil bacteria over North China Plain (NCP) with vast croplands has not yet been evaluated. In this study, high-resolution simulations are created to explore the HONO emission from soil bacteria over NCP and related in-fluences on atmospheric chemistry. Ground measurements of critical air pollutants including O-3, HONO, and PM2.5 compositions are incorporated to constrain the model simulations. Results show that abundant HONO is emitted from soil bacteria over NCP during summertime and the emission rate varies dramatically for different areas (about 0.2 kg km(-2) d(-1) - 2.0 kg km(-2) d(-1)). The HONO emission rate presents clear diurnal cycles with peaks of 1.5 kg km(-2) d(-1) in the afternoon and valleys of 0.4 kg km(-2) d(-1) during the early morning hours. The resulting HONO concentration ranges from 0.2 mu g m(-3) to 1.4 mu gm(-3), which predominates the total HONO concentration in ambient air, particularly in western NCP. The soil bacteria source can significantly alter the diurnal cycles of ambient HONO and OH concentrations over NCP, but only slightly change O-3 and PM2.5 concentrations via participating photochemistry and secondary aerosol formations. These results highlight the pressing need for the involvement of HONO emission from soil bacteria in modeling studies regarding atmo-spheric chemistry, particularly in rural areas
Effects of vegetation restoration types on soil nutrients and soil erodibility regulated by slope positions on the Loess Plateau
No full textSoil degradation is significantly increased driven by soil nutrient loss and soil erodibility, thus, hampering the sustainable development of the ecological environment and agricultural production. Vegetation restoration has been widely adopted to prevent soil degradation given its role in improving soil nutrients and soil erodibility. However, it is unclear which vegetation type has the best improving capacity from soil nutrient and soil erodibility perspectives. This study selected three vegetation restoration types of grasslands (GL), shrublands (SL), and forestlands (FL) along the five slope positions (i.e., top, upper, middle, lower, and foot slope), to investigate the effects of vegetation restoration types on soil nutrients and soil erodibility. All vegetation restoration types were restored for 20 years from croplands (CL). We used comprehensive soil nutrient index (CSNI) and comprehensive soil erodibility index (CSEI) formed by a weighted summation method to reflect the effect of vegetation restoration on the improving capacity of soil nutrient and erodibility. The results showed the vegetation types with the highest comprehensive soil quality index (CSQI) at the top, upper, middle, lower and foot slope were FL (1.92), FL (1.98), SL (2.15), FL (2.37) and GL (3.93), respectively. When only one vegetation type was considered on the entire slope, SL (0.59) and FL (0.59) had the highest CSNI, the SL had the lowest CSEI (0.34) and the highest CSQI (1.89). The CSNI was mainly influenced by soil structure stability index (SSSI), sand content, silt + clay particles, and CSEI was controlled by soil organic matter (SOM), macroaggregates and microaggregates. Moreover, the CSQI was influenced by pH, silt and clay content, and biome coverage (BC). The study suggested the SL were advised as the best vegetation restoration type on the whole slope from improving soil nutrients and soil erodibility
Seasonal and diurnal variation of PM2.5 HULIS over Xi'an in Northwest China: Optical properties, chemical functional group, and relationship with reactive oxygen species (ROS)
No full textHumic-like substances (HULIS) in particulate matter (PM) play critical roles in the atmospheric changes in our environment. In this study, high time resolution PM2.5 samples were collected to insight the abundances, spectroscopic characters, chemical groups, and oxidative potential of HULIS in Xi'an, China. The average mass concentrations of HULIS in term of carbon (HULIS-C) was 11.55 +/- 5.85 and 8.28 +/- 2.23 mu g C m(-3) in winter and summer, respectively. The diurnal variations of HULIS displayed three peaks (03:00-07:00, 10:00-14:00, and 18:00-21:00 LT) in winter, but a single peak (08:00-12:00 LT) in summer. The optical parameters show obvious difference between winter and summer. Fourier Transform infrared (FT-IR) spectra revealed that the HULIS mainly consisted of aliphatic chains, aromatic rings, and carboxylic groups. The FT-IR spectra proved that the aromatic compounds and carboxylic acids dominated the diurnal variation in winter, while carboxylic acids were responsible for that in summer. The normalized oxidative potential of HULIS exhibited an inverse trend with the HULIS-C concentration measured by the DCFH assay. The diurnal reactive oxygen species (ROS) productions from HULIS presents three valleys (03:00-07:00, 10:00-14:00, and 18:00-21:00 LT) in winter but only a single valley (08:00-12:00 LT) in summer. In addition, a positive correlation (R-2 approximate to 0.6, p<0.01) between the oxidative potential and specific ultraviolet absorbance at a wavelength of 254 nm (SUVA254) in winter suggested that the oxidative power of HULIS could be more related to the compounds with high light absorbance, high aromaticity,and molecular weight. The results of this study offer more solid knowledge on the spectral and chemical char- acteristics and oxidative potential of the HULIS in PM2.5 of the typical city in northwest China