Guangzhou Institute of Geochemistry
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The characterization of ambient levoglucosan in Beijing during summertime: Dynamic variation and source contributions under strong cooking influences
No full textParticulate levoglucosan is an important tracer for biomass burning emission in ambient air. However, recent studies question its reliability as a biomass burning tracer in Chinese mega cities due to important contribution from potential non-biomass burning sources, such as cooking. To address this, we examined the dynamic variation and sources of levoglucosan using a chemical ionization mass spectrometer and other advanced instruments during Beijing's summer of 2021. The average mass concentration of levoglucosan and its isomer (C6H10O5) was 0.025 +/- 0.014 pg/m(3) , constituting 0.55 % +/- 0.32 % of total organic carbon (OC) in this campaign. Despite cooking emissions contributing significantly to the organic aerosol (OA, 20 %), levoglucosan and its isomers correlated more strongly with biomass-burning related tracers ( R > 0.6), black carbon (R = 0.72) and less so with cooking-related sources (R = 0.3). This indicates that levoglucosan is primarily dominated by biomass-burning emis- sions rather than cooking in Beijing's urban areas during summertime. The diurnal varia- tion of levoglucosan concentrations highlighted the importance of daytime and nocturnal biomass burning emissions during polluted periods in Beijing. Using levoglucosan as a tracer to quantify the biomass burning OC (BBOC), we found good agreement on the time series of BBOC between the tracer method and other independent source apportionment method. This reaffirms the reliability of levoglucosan as a biomass burning tracer. Biomass burn- ing contributed an average of 7 %-8 % to OC, highlighting its significant impact on Beijing's summer air quality. Our study enhances understanding of biomass burning influences on ambient aerosol in typical urban areas. (c) 2025 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V
Mercury evidence for volcanism driving environmental changes during the protracted Late Ordovician mass extinction and early Silurian recovery
No full textVolcanism has been proposed as the trigger for the environmental perturbations and associated mass extinction during the Ordovician-Silurian (O-S) transition. However, the timing, duration, and intensity of volcanic eruptions during this critical period and their relationships to environmental perturbations and biotic changes remain unresolved. In this study, we use mercury (Hg) concentrations and isotopes from marine sediments in South China to reconstruct the evolution of volcanism from the Late Ordovician to early Silurian. Our results show that strong Hg enrichment coupled with generally near-zero to slightly positive Delta 199Hg values occurred before, during, and after the classically defined Late Ordovician Mass Extinction (LOME), suggesting a significant influx of volcanogenic Hg. The Hg enrichment intervals coincided with global warming, oceanic anoxia, and negative excursions in carbon and sulfur isotopes, suggesting that volcanism drove the environmental perturbations during the O-S transition. The coincidence of Hg enrichment with extinction horizons supports the hypothesis that volcanism may have contributed to LOME. Our study also suggests that volcanism persisted for approximately 3 million years after mass extinction and may have delayed the recovery of marine ecosystems during early Silurian
Magnesium Isotope Fractionation During Basalt Weathering: An Index of Weathering Fluxes and CO<sub>2</sub> Consumption
No full textThe weathering of silicate rocks exerts a significant control on the weathering fluxes of metals and atmospheric CO2 consumption. In this study, we present new magnesium (Mg) isotope data from a basalt weathering profile in Hainan Island, South China, to investigate Mg isotope fractionation and calculate weathering fluxes and CO2 consumption. The Mg mobility (tau(Mg,Ti)) in saprolites decreases from -34.1% to -95.7%. The delta Mg-26 values in saprolites vary from -0.25 +/- 0.07 parts per thousand to 0.43 +/- 0.07 parts per thousand, higher than those of the parent rock (-0.25 +/- 0.07 parts per thousand). The significant Mg loss during the formation and decomposition of clay minerals influences Mg isotope fractionation, particularly with changes in kaolinite structure under different pH conditions, which prefer heavy Mg isotopes. By applying a mass balance model, we have developed a novel method to calculate weathering fluxes based on the weathering profile, yielding Mg elemental fluxes (Mg-Flux) of 2.45-5.85 mol/cm(2)/Myr, Mg isotopic fluxes (delta Mg-26(Flux)) of -0.44 to -0.04 parts per thousand/mol/cm(2)/Myr, and CO2 consumption of 2.3 x 10(12) mol/yr for the weathering outputs of basaltic rocks. This highlights the crucial role of basalt weathering in global carbon sequestration. Our findings improve the understanding of Mg cycling and isotope fractionation in epigenetic environments and facilitate the quantification of weathering fluxes and atmospheric CO2 consumption during basalt weathering
Daytime Production of Airborne Pollutants Including Brown Carbon by NO<sub>2</sub> Interaction With Surface Microlayer of Lake Water in Southwestern China
No full textSurface microlayer at freshwater (rivers, lakes, ponds, streams, and groundwater) and seawater is abundant with organic compounds compared to subsurface water. These organics adsorbed at the air-water interface can interact with the atmospheric oxidants and influence the exchange of organic materials between the water and the atmosphere. Here, we assess the chemical interaction between gaseous NO2 and authentic surface microlayers collected at the lake water (Dianchi Lake) situated in China. The formation of the gas-phase product compounds was evaluated in real time using a novel secondary electrospray ionization ultrahigh-resolution quadrupole Orbitrap mass spectrometer (SESI-UHR-MS) upon exposure of surface microlayer to gaseous NO2 (20 or 50 ppb) in dark and under simulated sunlight irradiation at two different temperatures: 5 degrees C and 25 degrees C. The obtained results revealed that the sampling sites of the lake impacted by human activities (municipal sewage and agricultural activities) significantly impact the number and the composition of the formed gas-phase product compounds. The formation of nitrogen (N)-containing compounds was observed as well, which contain most likely nitro or amino functional groups, or alternatively, they could be aromatic compounds. The observed N-containing compounds may contribute to the "brown carbon" which act as light-absorbing compounds, thus influencing the radiative forcing of aerosols in the atmosphere
A Novel Land Surface Temperature Retrieval Algorithm for SDGSAT-1 Images
No full textLand surface temperature (LST) is a crucial parameter influencing Earth-atmosphere interactions and energy balance processes. The Sustainable Development Goals Science Satellite 1 (SDGSAT-1) was recently launched to support the realization of the United Nations Sustainable Development Goals (SDGs), which provides worldwide three-spectrum wide-swath, high-resolution, and high-sensitivity thermal infrared (TIR) images. The objective of this study is to develop a modified three-channel split-window algorithm incorporating atmospheric water vapor content (W-TCSW) for LST retrieval from SDGSAT-1 images. This algorithm was developed from the existing split-window (SW) form. The parameters of the algorithm were determined based on the MODerate resolution atmospheric TRANsmission (MODTRAN) simulation results of 946 Thermodynamic Initial-Guess Retrieval (TIGR) atmospheric profiles. The W-TCSW algorithm was comprehensively compared with the SW and three-channel SW (TCSW) algorithms. The retrieval results of the three algorithms were validated with simulated datasets and in situ measurements from the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) sites in China and the Surface Radiation Budget Network (SURFRAD) sites in USA. The SDGSAT-1 data retrieved by the W-TCSW algorithm was also intercompared with Landsat and ECOSTRESS LST products. The W-TCSW algorithm demonstrated the highest accuracy among the three retrieval algorithms (SW, TCSW, and W-TCSW). The influences of atmospheric water vapor content (AWVC) and land surface emissivity (LSE) as well as land use and land cover (LULC) on retrieval algorithms were discussed in a long-term time series. This study introduces a novel LST retrieval algorithm considering AWVC for SDGSAT-1 images and elucidates comprehensive validation and comparative assessment, expanding the application of high-spatial resolution TIR remote sensing data
P-wave attenuation variations beneath the central and western Tien Shan from teleseismic waves
No full textThe seismic attenuation plays an important role in understanding the subsurface structure and provides complementary information on the mantle dynamic together with seismic velocity information. Here we explore the attenuation structure beneath the central and western Tien Shan using teleseismic P-wave data. Firstly, we map the spatial distribution of relative attenuation parameter using the spectral ratio technique in the frequency band between 0.1 and 1.5 Hz. Our results reveal strong lateral attenuation variations in the lithosphere and asthenosphere underneath the study area. Then we invert for the Qp values using a linear inversion approach. Two high-attenuation regions are observed beneath the middle Tien Shan and western Tarim Basin that could be associated with upwelling hot materials and/or a small plume. Moreover, low-attenuation regions are found beneath the Kazakh Shield and western Tien Shan, which can be attributed to the underthrusted/subducted lithospheric fragments
Molecular and carbon isotopic geochemistry of oils with different fluorescence color from the Upper Jurassic Qigu formation and oil accumulation process in Yongjin area, Junggar Basin in China
No full textThe Yongjin area, located in the middle of the Junggar Basin, is an important oil-producing region. Its major oilproducing formation is the Upper Jurassic Qigu Formation, which has experienced multiple oil-charging events that have resulted in oils with various fluorescent colors. However, the source of oils from the Qigu Formation is currently debated. As exploration and development progressed, the productivity of the Qigu Formation was observed to vary owing to oil viscosity differences. Conventional extraction methods can only be used to obtain a mixture of fluorescing oils of different colors, making it difficult to analyze the properties of oils that charge during different periods. Using microscopy to observe fluorescence the characteristics of oil in various samples were analyzed. Then, accelerated sequential extraction was used to separate the oils with different fluorescent colors (Groups I-IV). Through GC-MS (gas chromatography), GC-IRMS (gas chromatography-mass spectrometry), FT-IR (fourier transform infrared spectroscopy), and fluid inclusion observations and measurements, in conjunction with the geological context, the sources of oils from different charge periods and genesis of heavy oil were determined and the process of oil accumulation was reconstructed. Three stages of oil charging were identified: (1) During the Middle to Late Jurassic, low-mature and mature oil from the Lower Permian Fengcheng Formation and a low quantity of low-mature oil from the Middle Permian Lower Wuerhe Formation charged the Qigu Formation. These oils underwent notable biodegradation and oxidation, with some captured by inclusions (Group III) for preservation. (2) During the Late Cretaceous to Early Paleogene, mature oil from the Wuerhe Formation charged the Qigu Formation. This oil mixed with early oil that was not captured by the inclusions, resulting in the formation of black-brown fluorescing oil (Group IV) and yellow fluorescing inclusion oil (Group II). (3) From the Late Paleogene to the present, highly mature condensates from the Lower Wuerhe Formation charged the Qigu Formation. The oil mixed with early oil to generate yellow-brown (Group II) and blue-white (Group I) fluorescing oils. Low-mature and mature oil from the Fengcheng Formation charged the Jurassic reservoirs and underwent secondary alteration, whereas high-mature oil and gas did not. These oils likely predominantly accumulated in reservoirs between the Fengcheng and Lower Wuerhe formations. Although the Jurassic source rocks began to generate oil, this oil did not migrate upward to the Qigu Formation, indicating that the conventional and unconventional reservoirs under the Jurassic Qigu Formation have exploration potential
Metamorphism and tectonics of a continental arc root: Insights from garnet amphibolite in the North Qaidam tectonic belt, northern Tibet
No full textThe architecture of continental arc crust from its surface to base is a crucial aspect of understanding long-term crustal growth and reworking. However, the timing and nature of metamorphism in the middle to lower crust are some of the least-understood components of continental arc systems. In this contribution, we integrate phase equilibrium modeling and zircon geochronology to determine the metamorphic history of garnet amphibolite in the North Wulan metamorphic complex, North Qaidam tectonic belt, northern Tibet, and then provide key insights into the metamorphic nature of the middle to lower crust of an early Paleozoic continental arc, and into orogenic geodynamic processes associated with the closure of the Proto-Tethyan Ocean. Garnet amphibolite contains a peak metamorphic assemblage of garnet + orthopyroxene + hornblende + plagioclase + ilmenite + quartz +/- biotite + melt, which defines a peak/near-peak pressuretemperature (P-T) range of 800-860 degrees C at 5-8.5 kbar, based on phase equilibrium modeling. Rounded inclusions of hornblende, plagioclase, and quartz in garnet porphyroblasts suggest prograde garnet growth at the expense of amphibole. Partial replacement of garnet and hornblende by orthopyroxene suggests high-T decompression after peak pressure. Post-peak partial replacement of garnet by plagioclase-quartz-hornblende or hornblende corona suggests decompression cooling after peak temperature. These results suggest that the garnet amphibolite records a clockwise P-T path with high-T decompression. These currently exposed granulitefacies rocks from the southern part of the North Wulan metamorphic complex represent a middle to lower crustal exposure (root) of an early Paleozoic continental arc-backarc setting (depths of >16-28 km) during the subduction of the Proto-Tethyan Ocean. Zircon petrochronology in garnet amphibolite reveals that protracted metamorphism occurred at ca. 515-449 Ma. These new insights into the early Paleozoic tectonometamorphic evolution of the North Wulan metamorphic complex constrain the northward subduction polarity of the South Qilian Ocean and the tectonic evolution of the North Qaidam tectonic belt. Clockwise P-T paths in continental arc settings are related to the thinning of the thickened arc crust triggered by the steepening of subducted oceanic slab, which is accompanied by slab retreat and rollback and could reflect the migration of continental arc magmatic axes. Our new results tie together high-resolution thermal, magmatic, and metamorphic records to explain the complex evolution of the roots of continental arc systems
Effect of A-Site Defects on the Catalytic Activity of Perovskite LaCoO<sub>3</sub>: Insights from the Electronic Structure
No full textThe development of highly active perovskite-based catalysts for the oxidation of volatile organic chemicals (VOCs) has drawn a great deal of attention. A-site defect regulation is found to be effective to improve the catalytic performance, but the relationship between structure variation and catalytic activity has not been clearly unveiled. Herein, this issue was interpreted by the variation of physicochemical properties and electronic structure (O p-band center). An in situ one-step calcination method with NH4HCO3 addition was adopted to prepare a series of A-site-deficient LaCoO3 perovskites (LxCO), which were characterized by XRD, TEM, EELS, ESR, XPS, UPS, H-2-TPR, and O-2-TPD and catalytic test toward toluene oxidation. The catalytic activity displayed a volcano-type relationship with an addition amount of NH4HCO3. The electronic structure determined the reducibility and active oxygen content and accordingly affected the catalytic activity of LxCO. The obtained results provide theoretical and technical support for the design of efficient VOC oxidation catalysts
Novel Analysis System for the Precise Measurement of Helium Concentration in Soil Gas Based on the Isotope Dilution Method
No full textDetection of abnormal helium concentration in soil gas is important for helium reservoir exploration. However, because of severe air mixing, helium concentration anomalies in soil gas are extremely weak, and a high-precision analysis system is required to discern them. In this study, we introduce a novel, fully automatic analysis system to determine the helium concentration in soil gas in static mode. The system includes a sample inlet device that can precisely measure the amount of soil gas entering the system, a pretreatment component for helium purification and separation, and a quadrupole mass spectrometer for measuring the helium concentration. The precision of this analysis system for air helium concentration was measured and found to be superior to 1%, sufficient to detect the weak helium concentration anomalies in soil gas. Establishing this method provides a high-efficiency and precise technical approach to identifying weak He concentration anomalies in environmental samples, which is beneficial for helium resource exploration