Institute of Earth Environment
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Microbial characteristics response to the soil quality of newly created farmland on the Loess Plateau
No full textMicrobiome plays an important role in evaluating soil quality for sustainable agriculture. However, the suitability of biological indicators in reclaimed farmland is less understood. Using high-throughput sequencing, we evaluated the soil microbial community of the newly created farmland (NF) after reclamation with two local high-yield farmlands (slope farmland (SF), check-dam farmland (CF)) on the Loess Plateau. Soil enzyme activities and the amount of culturable microorganism were also quantified to assess the soil quality. Results showed that the microbial diversity, cultural microorganism abundance, and soil enzyme activities indicated poor soil quality in NF. The dominant bacterial phyla were Proteobacteria, Bacteroidetes, Acidobacteria, and Cyanobacteria. The abundance of Acidobacteria was significantly lower in NF (13.31%) than in SF (27.25%) and CF (27.91%). Soil enzyme activities had a significant correlation with the abundance of culturable microorganism, Proteobacteria and Bacteroidetes, soil organic matter, total nitrogen, cation exchange capacity, and pH, suggesting that soil microbes have driven the formation of nutrition and further mediated crop growth. Therefore, the application of bacterial fertilizers could be a potential way to improve the soil quality of reclaimed farmland for crop growth
Oxygen vacancy-dependent photocatalytic activity of well-defined Bi2Sn2O7-x hollow nanocubes for NOx removal
No full textIntricate engineering of oxygen vacancies (OVs) to trap kinetically diffusible rarefied NO gas and to enhance the population of long-lived electrons remains a great challenge for NO removal in outdoor atmosphere. In this study, OV-engineered Bi2Sn2O7-x hollow nanocubes with distinct Sn/Bi-adjacent OVs were tightly managed and synthesized. Theoretical calculations and experimental studies revealed that not all types of OVs were beneficial for increasing the photoactivity owing to their different effects on the band structure and carrier diffusion path. Bi2Sn2O7-x with Sn-adjacent OVs could serve as adsorption sites, boosting rarefied NO enrichment and electron-hole separation. However, Bi2Sn2O7-x with Bi-adjacent OVs exhibited an opposite effect owing to increased charge recombination centers. Our findings highlight the importance of the character of OVs for efficient interface electron activation and for the removal of ambient rarefied gaseous pollutants
Possible obliquity-forced warmth in southern Asia during the last glacial stage
No full textOrbital-scale global climatic changes during the late Quaternary are dominated by high-latitude influenced -100,000-year global ice-age cycles and monsoon influenced -23,000-year low-latitude hydroclimate variations. However, the shortage of highly-resolved land temperature records remains a limiting factor for achieving a comprehensive understanding of long-term low-latitude terrestrial climatic changes. Here, we report paired mean annual air temperature (MAAT) and monsoon intensity proxy records over the past 88,000 years from Lake Tengchongqinghai in southwestern China. While summer monsoon intensity follows the -23,000-year precession beat found also in previous studies, we identify previously unrecognized warm periods at 88,000 & ndash;71,000 and 45,000 & ndash;22,000 years ago, with 2 & ndash;3 degrees C amplitudes that are close to our recorded full glacial-interglacial range. Using advanced transient climate simulations and comparing with forcing factors, we find that these warm periods in our MAAT record probably depends on local annual mean insolation, which is controlled by Earth & rsquo;s -41,000-year obliquity cycles and is anti-phased to annual mean insolation at high latitudes. The coincidence of our identified warm periods and intervals of high-frequent dated archaeological evidence highlights the importance of temperature on anatomically modern humans in Asia during the last glacial stage.
(c) 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved
A data-model comparison pinpoints Holocene spatiotemporal pattern of East Asian summer monsoon
No full textConflicting reconstructions of Holocene variability of the East Asian summer monsoon (EASM) from speleothem versus other types of proxy records have yielded widely divergent estimates of its phase relationship with the Indian summer monsoon (ISM) and Northern Hemisphere summer insolation (NHSI). This apparent discrepancy has been partly attributed to the uncertainties in the climatic representation of Chinese speleothem oxygen isotope (delta O-18) records. Here we present a composite speleothem delta O-18 record of the last similar to 14 kyr from Shennong Cave in southeastern China and model-simulated data of rainfall and meteoric delta O-18 over eastern China. Our synthesis of the proxy-model data suggests that the spatial patterns in both speleothem delta O-18 and paleo-rainfall over eastern China during the Holocene are diverse at orbital and multi-millennial scales. Our findings imply that: 1) speleothem delta O-18 in the EASM regime is largely controlled by the large-scale circulation and concomitant latitudinal shifts of the monsoon rain belt; notwithstanding the heterogeneous spatiotemporal pattern of Holocene rainfall as inferred from various proxy records, a coherent orbital-scale speleothem delta O-18 variability across most Asian monsoon regions (except southeastern China) indeed stems from the NHSI-forced changes in overall monsoon intensity; overall monsoon intensity is not equivalent to monsoon rainfall amount but a manifestation of the large-scale atmospheric circulation; 2) divergent phase relationships with NHSI between speleothem delta O-18 and other proxy records are consistent withdrather than contradictory todthe NHSI forcing mechanism. Speleothem delta O-18 and rainfall records reflect two different aspects of the monsoon dynamics. These results may thus, largely help to reconcile the divergent views of the Holocene Asian monsoon variability. (C) 2021 Elsevier Ltd. All rights reserved
Complex anthropogenic interaction on vegetation greening in the Chinese Loess Plateau
No full textVegetation greening steered by land use management in the Chinese Loess Plateau has been widely reported, however studies that quantitatively assessing and explicitly linking the anthropogenic forcing on vegetation greening and browning are scarce. Here in this study, we calculate the increment and rate of change of fractional vegetation cover (FVC) from 1998 to 2018 in the Loess Plateau, and compare the results with changing rainfall, soil types, and Gross Domestic Product (GDP), to detail a systematic assessment of the role of the climate-vegetation-human nexus. We have observed that nearly 80% of the study area has undergone greening, and no-ticed that rainfall was not the main driver of rapid vegetation change, instead of human land use management such as, irrigation along the Yellow River, snowmelt-runoff irrigation, and irrigation from reservoirs formed by check dams contributed the most for the increased FVC in the Chinese Loess Plateau. Concurrently, rapid vegeta-tion browning is almost fully driven by urban expansion. Our findings show that GDP growth promotes both browning and greening, indicative of sustainable development in the Loess plateau region. These contrasting trends reveal that the relationship between human activities and greening is very complex. (c) 2021 Elsevier B.V. All rights reserved
Determination of iodine-129 in twenty soil and sediment reference materials
No full textIncreasing attention has been paid to I-129 in soils and sediments for the purpose of environmental radioactivity monitoring, and understanding historic nuclear activities and their impacts. Accurate measurement of I-129 is vital, which greatly increases the requirement of various certified reference materials (CRMs). However, only a few CRMs with low levels of I-129 are available for accurate determination of I-129 in samples remote from nuclear sites and facilities. Here, this work investigated the concentrations of I-129 and I-127, and I-129/I-127 atomic ratios in twenty Chinese soil and sediment CRMs commercially available, as well as one in-house soil standard material (XASTD), with high-temperature pyrolysis combustion coupled with ICP-MS and accelerator mass spectrometry (AMS) measurements. This study demonstrates that I-129 concentrations in the twenty CRMs and one laboratory soil standard range from 0.31 x 10(6) atoms per g to 34.7 x 10(6) atoms per g, which were 1-4 orders of magnitude lower than those of the reference materials in use. For accurate measurement of I-129, the effect of salinity content in the samples on the iodine current intensity of the AMS measurement is firstly discussed. Significant salinity effect occurred when a high-salinity sample is analysed, which is likely due to the formation of abundant strong oxidants during the pyrolysis process, resulting in the existence of iodine as iodate instead of iodide. And finally, an analytical procedure is recommended for the low- and high-salinity soil and sediment samples. In summary, the reported data of the CRMs and the laboratory in-house control soil standard would broaden the group of available reference materials, be useful for method development of low-level I-129 samples, interlaboratory comparison and short- and long-term quality control, as well as extend I-129 applications in geological, environmental and nuclear sciences
Secondary Organic Aerosol Formation of Fleet Vehicle Emissions in China: Potential Seasonality of Spatial Distributions
No full textVehicle emissions are an important source of urban particular matter. To investigate the secondary organic aerosol (SOA) formation potential of real-world vehicle emissions, we exposed on-road air in Beijing to hydroxyl radicals generated in an oxidation flow reactor (OFR) under high-NOx conditions on-board a mobile laboratory and characterized SOA and their precursors with a suite of state-of-the-art instrumentation. The OFR produced 10-170 mu g m(-3) of SOA with a maximum SOA formation potential of 39-50 mu g m(-3) ppmv(-1) CO that occurred following an integrated OH exposure of (1.3-2.0) x 10(11) molecules cm(-3) s. The results indicate relatively shorter photochemical ages for maximum SOA production than previous OFR results obtained under low-NOx conditions. Such timescales represent the balance of functionalization and fragmentation, possibly resulting in different spatial distributions of SOA in different seasons as the oxidant level changes. The detected precursors may explain as much as 13% of the observed SOA with the remaining plausibly contributed by the oxidation of undetected intermediate-volatility organic compounds. Extrapolation of the results suggests an annual SOA production rate of 0.78 Tg yr(-1) from mobile gasoline sources in China, highlighting the importance of effective regulation of gaseous vehicular precursors to improve air quality in the future
The maximum carbonyl ratio (MCR) as a new index for the structural classification of secondary organic aerosol components
No full textRationale Organic aerosols (OA) account for a large fraction of atmospheric fine particulate matter and thus are affecting climate and public health. Elucidation of the chemical composition of OA is the key for addressing the role of ambient fine particles at the atmosphere-biosphere interface and mass spectrometry is the main method to achieve this goal.
Methods High-resolution mass spectrometry (HRMS) is on its way to becoming one of the most prominent analytical techniques, also for the analysis of atmospheric aerosols. The combination of high mass resolution and accurate mass determination allows the elemental compositions of numerous compounds to be easily elucidated. Here a new parameter for the improved classification of OA is introduced - the maximum carbonyl ratio (MCR) - which is directly derived from the molecular composition and is particularly suitable for the identification and characterization of secondary organic aerosols (SOA).
Results The concept is exemplified by the analysis of ambient OA samples from two measurement sites (Hyytiala, Finland; Beijing, China) and of laboratory-generated SOA based on ultrahigh-performance liquid chromatography (UHPLC) coupled to Orbitrap MS. To interpret the results, MCR-Van Krevelen (VK) diagrams are generated for the different OA samples and the individual compounds are categorized into specific areas in the diagrams. The results show that the MCR index is a valuable parameter for representing atmospheric SOA components in composition and structure-dependent visualization tools such as VK diagrams.
Conclusions The MCR index is suggested as a tool for a better characterization of the sources and the processing of atmospheric OA components based on HRMS data. Since the MCR contains information on the concentration of highly electrophilic organic compounds in particulate matter (PM) as well as on the concentration of organic (hydro)peroxides, the MCR could be a promising metric for identifying health-related particulate matter parameters by HRMS
Brownness of Organic Aerosol over the United States: Evidence for Seasonal Biomass Burning and Photobleaching Effects
No full textLight-absorptivity of organic aerosol may play an important role in visibility and climate forcing, but it has not been assessed as extensively as black carbon (BC) aerosol. Based on multiwavelength thermal/optical analysis and spectral mass balance, this study quantifies BC for the U.S. Interagency Monitoring of Protected Visual Environments (IMPROVE) network while developing a brownness index (gamma(Br)) for non-BC organic carbon (OC*) to illustrate the spatiotemporal trends of light-absorbing brown carbon (BrC) content. OC* light absorption efficiencies range from 0 to 3.1 m(2) gC(-1) at 405 nm, corresponding to the lowest and highest BrC content of 0 and 100%, respectively. BC, OC*, and gamma(Br) explain >97% of the variability of measured spectral light absorption (405-980 nm) across 158 IMPROVE sites. Network-average OC* light absorptions at 405 nm are 50 and 28% those for BC over rural and urban areas, respectively. Larger organic fractions of light absorption occur in winter, partially due to higher organic brownness. Winter gamma(Br) exhibits a dramatic regional/urban-rural contrast consistent with anthropogenic BrC emissions from residential wood combustion. The spatial differences diminish to uniformly low gamma(Br) in summer, suggesting effective BrC photobleaching over the midlatitudes. An empirical relationship between BC, ambient temperature, and gamma(Br) is established, which can facilitate the incorporation of organic aerosol absorptivity into climate and visibility models that currently assume either zero or static organic light absorption efficiencies
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