Institute of Earth Environment
Institutional Repository of Institute of Earth Environment, CASNot a member yet
7120 research outputs found
Sort by
Asynchronous variations of East Asian summer monsoon, vegetation and soil formation at Yulin (North China) in the Holocene
No full textIn the East Asian monsoon region, Chinese speleothem delta O-18 records exhibit a maximum monsoon strength during the early Holocene. However, other proxy data from lakes or loess, interpreted as monsoon rainfall, show a mid-Holocene monsoon optimum. This discrepancy may come from specific climate interpretation of different proxies. Here we report multiproxy records from a single loess-palaeosol sequence at Yulin in the monsoon marginal northern China, based on an independent and high-precision chronology. Our long-chain n-alkane delta D values, together with related biomarker proxies including the average chain length and concentration of long-chain n-alkanes, reveal a weakening trend in monsoon strength and less woody vegetation since similar to 6 ka. However, other soil formation-related proxies, such as magnetic susceptibility, grain-size distribution and total organic carbon, show a decreasing trend since 4-3 ka. We find that monsoon and vegetation are controlled by insolation variation, while soil formation is more related to temperature and humidity changes. Our multiple proxy comparison reveals different controlling mechanisms leading to different interpretations in monsoon, vegetation and soil formation reconstructions. This finding suggests that previous debates on Holocene monsoon changes in East Asia probably stem from the specific proxy interpretation. (C) 2022 John Wiley & Sons, Ltd
Lipid biomarkers in Lake Wudalianchi record abrupt environmental changes from the volcanic eruption in 1776
No full textVolcanic eruptions can cause abrupt changes in surrounding environments, but detailed sediment records of such changes are rare. The very high sediment accumulation rate in Lake Wudalianchi, a volcanic-dammed freshwater lake in northeastern China, provides an excellent opportunity for reconstructing volcanic-induced environmental change. Here we use multiple lipid biomarkers to reconstruct changes in aquatic ecosystems, hydrology, and methane cycling before and after a regional explosive volcanic eruption in 1776. Our results indicate that the Wudalianchi catchment was a shallow organic-rich marsh environment with abundant aquatic emergent macrophytes and an intense microbial methane cycle before the volcanic eruption. Following the volcanic eruption, the marsh was rapidly transformed into an oligohaline lake environment due to river channel damming by lava. Associated with the abrupt environmental change, we observe corresponding changes of cyclisation ratios of branched glycerol dialkyl glycerol tetraethers or brGDGTs (CBT and CBT ' indices), and the inferred pH displays an abrupt increase of -1.3. Group 1 alkenones emerge abruptly after the eruption when the inferred pH exceeds 8. Our results provide the first high-resolution reconstruction of environmental change induced by volcanic eruption and demonstrate the high efficacy of the lipid biomarkers in recording aquatic and terrestrial changes
Large contribution from worship activities to the atmospheric soot particles in northwest China
No full textWorship activities like burning joss paper during the Chinese Hanyi festival is a common, traditional custom in northwest China. However, the pollutants of e.g., soot particles, released from joss paper burning and the cor-responding impacts on urban air quality were poorly investigated, which can be a particular concern since these activities are conducted in an uncontrolled manner. In this study, a long time-of-flight (LToF) soot particle aerosol mass spectrometry (SP-AMS) was deployed to characterize the refractory black carbon (rBC) emitted from the joss paper burning, as well as crop residue, coal combustion, and traffic during the Hanyi Festival in mid-November 2020 in the northwestern city of Xi'an in China. Large difference (from 5% to 100%) in the fragmentation patterns (C-n(+)) for the measured rBC from different source emissions were found when compared to the reference Regal Black. Using the receptor model of positive matrix factorization (PMF) with the multilinear engine (ME-2) algorithm, the obtained rBC mass spectra were used as the anchoring profiles to evaluate the emission strengths of different source types to the atmospheric rBC. Our results show that the burning of joss paper accounted for up to 42% of the atmospheric rBC mass, higher than traffic (14-17%), crop residue (10-17%), coal (18-20%) during the Hanyi festival in northwest China. Moreover, we show that the overall air quality can be worsened due to the practice of uncontrolled burning of joss paper during the festival, which is not just confined to the people who do the burning. Although worship activities occur mainly during festival periods, the pollution events contributed by joss paper burning may pose an acute exposure risk for public health. This is particularly important since burning joss paper during worship activities is common in China and most Asian countries with similar traditions
Source profiles of molecular structure and light absorption of PM2.5 brown carbon from residential coal combustion emission in Northwestern China
No full textResidential coal combustion is a prominent source of brown carbon (BrC) aerosols, but knowledge of their molecular structures and optical absorption were limited, which have notable used in ambient BrC source identification and radiative forcing calculation. In this study, the Fourier transform-ion cyclotron resonance mass spectrometry combined with partial least squares regression analysis as well as Fourier transform infrared spectroscopy analysis were used to insight the molecular compounds and structures of BrC from anthracite and bituminous coal combustions between traditional and improved stoves. The absorption angstrom ngstro center dot m exponents (AAE) and mass absorption efficiency (MAE) values for the BrC emitted from the combinations of bituminous were both 1.2-2.5 times lower than those of anthracite, interpreting that the BrC from the anthracite emissions had greater light-absorbing capacity. In contrast, the emission factor of light absorption (EFAbs) at 365 nm for the bituminous coal combusted in the traditional stove was the highest among all the tested scenarios, which revealed that the incomplete combustion of bituminous coal could emit more BrC. It was noted that primary BrC emitted from the coal combustion with traditional stoves contains higher aromaticity groups of C-C and C=O and higher S containing organics, whereas more aliphatic groups were found in BrC using the improved stoves. N-containing (CHON and CHONS) compounds were dominated in the total molecular formula of BrC, whereas the sum of CHON and CHO groups had high double-bond equivalent (DBE) values contributed 53.5%-87.1% to the total BrC absorption. Moreover, for CHOS, the lowest of estimated molecular absorption, DBE, and DBE/C should attribute to the non-chromophoric or weak absorptive S-containing compounds. This study supplied an effective evaluation method to compare BrC emissions and their absorption for coal combustion on regional scale
Soil erosion and human activities over the last 60 years revealed by magnetism, particle size and minerals of check dams sediments on the Chinese Loess Plateau
No full textSoil erosion has become more serious in semiarid areas around the world. However, the discrimination of the impact of concurrent climate change and human activity on soil erosion in a particular study area remains a challenge. Check dams are important engineering measures to prevent soil erosion on the Chinese Loess Plateau, and the dam sediments, as the product of soil erosion, are related to both climate change and human activities in a small watershed. The present study selected a check dams sediment profile in the upper Jinghe Basin on the Chinese Loess Plateau as a case study. Based on AMS C-14 dating and Cs-137 measurement, we established the soil erosion timescale and employed multiple methods including magnetic susceptibility, particle size, and minerals to trace the soil erosion history. We compared them with a local hydrometeorological record in the Jinghe Basin to explore the relationship between soil erosion and human activities. AMS C-14 and Cs-137 results indicated that the profile was deposited since 1953. The results of magnetic susceptibility, particle size, and minerals revealed 3 soil erosion phases during the last 60 years. Soil erosion in this region is not only related to precipitation changes, but also closely related to human activities. Prior to the Reform and Opening-up in China in 1978, climatic change played a leading role in check dams sedimentation and hydrological changes. Subsequently, despite accelerated soil erosion associated with the family contract responsibility system, the check dams, afforestation and a warmer climate mitigated the soil erosion to some extent, runoff and sediment load continued to decrease. Since 1999, China's Grain for Green project has greatly reduced the runoff and sediment load. However, the policy of filling gullies and creating land since 2010 should be reconsidered carefully in terms of all aspects, including the eco-environment, hydrological cycle, and economics
How is the El Nino-Southern Oscillation signal recorded by tree-ring oxygen isotopes in southeastern China?
No full textPrevious studies universally found that tree-ring oxygen isotope (delta O-18(TR)) in southeastern China (SEC) significantly recorded the El Nino-Southern Oscillation (ENSO) signal. However, the correlation between the climate in SEC and ENSO is insignificant, so the local climatic response of SEC delta O-18(TR) fails to explain the significant positive correlations between these delta O-18(TR) records and ENSO. In this study, based on four delta O-18(TR) series from SEC, meteorological data, simulated precipitation oxygen isotope (delta O-18(P)) data, and a moisture uptake atlas deduced from Lagrangian backward trajectory experiments, a conceptual model was established to explain how the ENSO signal is recorded by SEC delta O-18(TR). During the El Nino decaying years, the Northwest Pacific (NWP) convective activity weakens; the convective weakening areas coincide with the main moisture sources for SEC, which enriches O-18 in moisture that is transported to SEC, resulting in positive anomalies of delta O-18(P) in SEC; finally, the ENSO-modulated delta O-18(P) signal is inherited by SEC delta O-18(TR). The opposite situations occur in the La Nina events. It was also indicated that the change in the moisture contribution percentage from different sources may not be a primary factor that connects SEC delta O-18(TR) with ENSO. These findings contribute to understanding climatic signals represented by delta O-18(TR) and delta O-18(P) in the East Asian monsoon region
Unraveling the process of aerosols secondary formation and removal based on cosmogenic beryllium-7 and beryllium-10
No full textThe secondary formation and diffusion processes of aerosol are extraordinarily complex and significantly impact the environment and human health. Therefore, exploring the process of aerosol formation and diffusion based on independent new tracer has always been a concern. The Be-7 and Be-10, which are generated only by the action of cosmic rays, are chemically stable and adsorbed on aerosol for transmission, so they have the potential characteristics of aerosol tracers. Here, we obtained the daily resolution atmospheric Be-7, Be-10, and Be-10/Be-7 without dust interference in Xi'an autumn and winter (heavy pollution period in a typical polluted area) by accelerator mass spectrometry. It is found that during the rapid formation of secondary aerosols (SA) under the stable Be-10/Be-7 ratio, which indicates the stable atmospheric vertical structure, the concentration of Be-7 and Be-10 is significantly negatively correlated (R-2 > 0.9) with the aerosol concentration. Therefore, SA relative content in aerosols can be estimated by the dilution amount of Be-7 and Be-10 to reveal the secondary-formation process of aerosol (33% average contribution to aerosols during the winter heavy air pollution period). Furthermore, we also revealed the physical removal process of aerosols based on Be-7, Be-10, and Be-10/Be-7, including precipitation removal and diffusion of vertical atmospheric movement caused by stratospheric air intrusion. In summary, meteoric cosmogenic 7Be and 10Be will provide a new way to study the secondary chemical formation and physical removal of aerosols
The Reading Palaeofire Database: an expanded global resource to document changes in fire regimes from sedimentary charcoal records
No full textSedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b - Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345
C-13 signatures of aerosol organic and elemental carbon from major combustion sources in China compared to worldwide estimates
No full textCarbon isotope signatures are used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions) using a dual 14C-13C isotope approach. The dual-isotope source apportionment crucially relies on accurate knowledge of 13C source signatures, which are seldom measured for EC. In this work, we present 13C signatures of organic carbon (OC) and EC for relevant sources in China. EC was isolated for 13C analysis based on the OC/EC split point of a thermal-optical method (EUSAAR_2 protocol). A series of sensitivity studies were conducted to investigate the EC separation and the relationship of the thermal-optical method to other EC isolation methods. Our results show that, first, the 13C signatures of raw materials and EC related to traffic emissions can be separated into three groups according to geographical location. Second, the 13C signature of OC emitted by the flaming combustion of C4 plants is strongly depleted in 13C compared to the source materials, and therefore EC is a better tracer for this source than total carbon (TC). A comprehensive literature review of 13C source signatures (of raw materials, of TC, and of EC isolated using a variety of thermal methods) was conducted. Accordingly, we recommend composite 13C source signatures of EC with uncertainties and detailed application conditions. Using these source signatures of EC in an example dual-isotope source apportionment study shows an improvement in precision. In addition, 13C signatures of OC were measured at three different desorption temperatures roughly corresponding to semi-volatile, lowvolatile, and non-volatile OC fractions. Each source category shows a characteristic trend of 13C signatures with desorption temperature, which is likely related to different OC formation processes during combustion. (c) 2021 Elsevier B.V. All rights reserved
Effects of hydroperoxy radical heterogeneous loss on the summertime ozone formation in the North China Plain
No full textHydroperoxy radical (HO2) is a crucial oxidant participating in the oxidation of nitrogen oxide to nitrogen dioxide which constitutes one of the most important pathways for the ozone (O-3) photochemical formation in the troposphere. Laboratory experiments and field observations have revealed efficient HO2 heterogeneous uptake on wet aerosols, but its impact on the O-3 formation remains controversial. A severe and persistent O-3 pollution episode has been simulated using the WRF-Chem model to evaluate the impacts of the HO2 heterogeneous loss on the O-3 formation in the North China Plain (NCP) during the summertime of 2018. Comparisons between experimental simulations with the HO2 effective uptake coefficient of 0.2 and 0.0 shows that the HO2 heterogeneous loss decreases the daytime HO2 and maximum daily average 8-hour (MDA8) O-3 concentrations by about 5% and 1% in the NCP, respectively. Emission mitigation from 2013 to 2018 is found to contribute a 2.1 mu g m(-3) (5%) increase in the MDA8 O-3 concentration due to decreased aerosol sink for the HO2 heterogeneous loss in the NCP. Our results reveal that decreased HO2 heteroge-neous uptake does not constitute an important factor driving the O-3 trend since 2013 in the NCP