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Synchronous Sedimentation in Gonjo Basin, Southeast Tibet in Response to India-Asia Collision Constrained by Magnetostratigraphy
No full textThe India-Asia collision has been the object of vigorous debate for decades, with ages of the start ranging from Late Cretaceous to Oligocene. Sedimentary records preserved in both near-field and far-field settings provide critical evidence concerning the age and mechanism of the collision. Gonjo Basin, one of a series of fault-controlled basins developed along the eastern margin of Tibetan Plateau, contains well-exposed sedimentary successions, providing great potential for understanding depositional, tectonic-geomorphological and climatic history associated with India-Asia collision and plateau uplift. Lithofacies analysis reveals that the sequences consist of sandstone, mudstone and conglomerate, formed in fluvial-lacustrine systems. High-resolution magnetostratigraphy, constrained by U-Pb dating of zircon from a volcaniclastic layer which has been found in the central Gonjo Basin for the first time, indicates that sedimentation started at 69 Ma and continued in this locality until 50 Ma. Anisotropy of magnetic susceptibility (AMS) interpretation based on the age framework reveals a post-depositional compression after 50 Ma, responding simultaneously to the early uplift of southeast Tibetan Plateau driven by India-Asia collision
Synchronous changes in the East Asian-Australian summer monsoons around 7.2 ka
No full textPrevious evidence has identified the presence of numerous abrupt changes in the East Asian-Australian summer monsoons (EAASMs) on centennial to millennial timescales during the Holocene, which are tightly coupled with high northern latitude cooling anomalies. However, less attention has been paid to spatial characteristics in the EAASMs during the 7.2 ka event. Here a series of hydrological records from the EAASMs region are systematically integrated to improve understanding of the spatial precipitation distributions in the EAASMs region around 7.2 ka. The results show significant dry conditions in northern China, but relatively dry conditions or dry-to-wet shifts in southern tropical China around 7.2 ka, distinctly indicating an abrupt collapse of the East Asian summer monsoon during the 7.2 ka event. A similar pattern is also observed in the Australian summer monsoon region. The precipitation in northern Australia and its adjacent seas abruptly decreases around 7.2 ka, whereas it takes on a slight increase with a dry-to-wet shift near the center of the Indo-Pacific warm pool region. Therefore, it seems that synchronous collapse in the EAASMs occurs during the 7.2 ka event, which is different from a see-saw in the EAASMs during the 8.2 ka event. And it is inferred that synchronous changes in the EAASMs at the 7.2 ka event is probably a response to a low solar irradiance superimposed with influence of the volcanic eruption and ENSO activities
Photocatalytic reactive oxygen species generation activity of TiO2 improved by the modification of persistent free radicals
No full textEnvironmentally persistent free radicals (EPFRs) may help mineral dust to produce more reactive oxygen species (ROS). However, the mechanism of this effect is not yet clear. Therefore, in this study, anatase modified with EPFRs was synthesized via a simple two-step method. The presence of EPFRs was confirmed using a series of characterization techniques, including electron paramagnetic resonance and nuclear magnetic resonance. Herein, we found that EPFRs can improve OH generation via the oxidation reaction between photogenerated holes (h(+)) and OH- (or H2O). This result was due to two reasons. The first is that the EPFRs construct a built-in electric field, which helps the migration of h(+) from the bulk to the surface of anatase and then to EPFRs. The other reason is that EPFRs help anatase adsorb more H2O molecules, which are then oxidized to OH by h(+). This study will help to understand the photochemical production mechanism of ROS on the surface of mineral dust
Eccentricity-paced monsoon variability on the northeastern Tibetan Plateau in the Late Oligocene high CO2 world
No full textConstraining monsoon variability and dynamics in the warm unipolar icehouse world of the Late Oligocene can provide important clues to future climate responses to global warming. Here, we present a similar to 4-thousand year (ka) resolution rubidium-to-strontium ratio and magnetic susceptibility records between 28.1 and 24.1 million years ago from a distal alluvial sedimentary sequence in the Lanzhou Basin (China) on the northeastern Tibetan Plateau margin. These Asian monsoon precipitation records exhibit prominent short (similar to 110-ka) and long (405-ka) eccentricity cycles throughout the Late Oligocene, with a weak expression of obliquity (41-ka) and precession (19-ka and 23-ka) cycles. We conclude that a combination of eccentricity-modulated low-latitude summer insolation and glacial-interglacial Antarctic Ice Sheet fluctuations drove the eccentricity-paced precipitation variability on the northeastern Tibetan Plateau in the Late Oligocene high CO2 world by governing regional temperatures, water vapor loading in the western Pacific and Indian Oceans, and the Asian monsoon intensity and displacement
Comparison of Equivalent Doses Obtained with Various post-IR IRSL Dating Protocols of K-Feldspar
No full textFive dating protocols with post-infrared infrared (IR) stimulated luminescence signals (i.e. pIRIR) were performed on the K-feldspar of loess samples. Two of them were the single-aliquot regenerative-dose protocol (SAR) with two-step pIRIR stimulation, with the first IR stimulation at 50 degrees C or 200 degrees C and the second at 290 degrees C (pIR(50)IR(290), pIR(200)IR(290)). Two of them were the SAR protocols with five-step or six-step IR stimulation at multiple elevated temperatures to 250 degrees C or 300 degrees C (MET-pIRIR(250), MET-pIRIR(300)). The final one was the multiple-aliquot regenerative-dose (MAR) protocol with the MET-pIRIR(300) signal, together with a 500 degrees C heat treatment administered before the test dose ('MAR with heat'). The results show that when the equivalent dose (D-e) of the sample was less than 500 Gy, all of the protocols gave consistent results; however, when D-e exceeded 750 Gy, all of the SAR protocols underestimated D-e. The pIR(50)IR(290) signal had the highest degree of underestimation, while the pIR(200)IR(290), MET-pIRIR(250) and MET-pIRIR(300) signals had similar D-e values and similar degrees of underestimation. Possible reasons for the SAR D-e underestimation are discussed. We suggest that only the 'MAR with heat' protocol is suitable for samples with D-e exceeding 750 Gy
Spatio-temporal variability of atmospheric CO2 and its main causes: A case study in Xi'an city, China
No full textCities account for most anthropogenic carbon dioxide (CO2) emissions, and thus play an important role in carbon mitigation. However, the variability of atmospheric CO2 caused by the complex emission sources and topography within city remains a challenge in evaluating urban CO2 emissions. Specifically, the mechanism of spatial and temporal patterns is still unclear at city scale. In this work, we explored the spatial and seasonal patterns of atmospheric CO2 at the city scale in Xi'an and attempted to illustrate the mechanisms of these patterns based on the analysis of CO2 sources and sinks. Using the observed radiocarbon (C-14) in atmospheric CO2 as a tracer, we determined the CO2 emissions from fossil fuel (CO2ff) and the biosphere (CO2bio) in different seasons and city areas. The results showed that CO2ff in urban areas is significantly (p < 0.05) higher than that in suburban areas, and explained 82% and 74% of the spatial differences in winter and summer, respectively. Based on the analysis of delta C-13 of CO2 in the local sources, the depleted delta C-13 of urban site indicated greater influences from traffic or natural gas in the urban area than that in the suburban area. These findings suggest that the spatial differences of atmospheric CO2 are dominated by different emission intensities of fossil fuels between urban and suburban areas. In contrast, the contributions of CO2ff to the seasonal variations of atmospheric CO2 were different between urban and suburban areas, that is CO2ff contributed as much as CO2bio to the seasonal variations of atmospheric CO2 in suburban area, but the contribution increased with the increasing of human activities from suburban to urban area, and accounted for 57% of seasonal variations of atmospheric CO2 in the urban area. In addition, we also found that under the influence of the special topography of Xi'an city, the frequent fluctuations of atmospheric CO2 concentration in winter largely depend on the different wind conditions
Determination of ultra-low U-236 in environment samples using ICP-MS/MS measurement and chemical separation
No full textU-236 in the environment mainly originates from human nuclear activities. Based on the unique properties of uranium, U-236 can be used as a powerful tracer for investigation of oceanographic and environmental processes. This requires sensitive measuement of U-236 in various environmental samples. Due to the ultra-low radioactive level of U-236 in the environment, its measurement is only possible by mass spectrometry. Because of the low atomic ratio of 2(36)U/U-235 down to 10(-7)-10(-5) in the environment, the interferences of (UH+)-U-235-H-1 and peak tailings of U-235 and U-238 are critical challenges in the measurement of U-236 by ICP-MS. This work developed a sensitive ICP-MS/MS method for measurement of ultra-low U-236 by employing reaction cell technique and sequential quadrupole mass separators. By using 0.6 mL min(-1) CO2 - 7 mL min(-1) helium as collision/reaction gas to convert U+ and UH+ to UO+, the interferences of UH+ (UOH+/UO+ ratio) were significantly reduced to less than 2.4 x 10(-7). A minimum detectable U-236/U-238 ratio of 3.0 x 10(-1)0 was achieved, which is one order of magnitude better than reported values. By using collision focusing with helium in the reaction cell and APEX sample introduction system, the measurement sensitivity for U-236 (236UO(+)) was improved to 7.5 x 10(6) cps ppb(-1). In combination with an effective chemical separation of uranium from sample matrix and interferences using total borate fusion following extraction chromatography with UTEVA resin, a detection limit of 7.2 x 10(-1)6 g g(-1) for 236U was achieved. The developed method was verified by analysis of certified reference materials and by comparison with AMS measurement method. Soil samples collected from Northwest China were successfully analyzed. U-236/U-238 ratios down to 9 x 10(-10) were measured in these samples, and the sources of U-236 in different sits were discussed
Parent, alkylated, oxygenated and nitrated polycyclic aromatic hydrocarbons in PM2.5 emitted from residential biomass burning and coal combustion: A novel database of 14 heating scenarios
No full textTo characterize the emissions of polycyclic aromatic hydrocarbons (PAHs) from residential biomass burning and coal combustion in field environments, smoke samples were collected from the combustion of six types of biomass in heated kangs and four types of coal in traditional stoves and semi-gasifier stoves. The emission factors (EFs) of the total PAH were in the range of 84.5-344 mg/kg for biomass burning, with lower EFs for biomass with higher densities, and in the range of 38.0-206 mg/kg for coal combustion, with lower EFs for coals with higher maturity. Moreover, EFs were lower from high-density biomass fuels (wood trunk, 84.5 +/- 11.3 mg/kg) than low-maturity coals (bituminous coal, 206 +/- 16.5 mg/kg). Parent, oxygenated, alkylated, and nitrated PAHs accounted for 81.1%, 12.6%, 6.2%, and 0.1%, respectively, of the total-PAH EFs from biomass burning, and 84.7%, 13.8%, 1.4%, and 0.1%, respectively, of the total-PAH EFs from coal combustion. PAH source profiles differed negligibly between biomass fuels but differed significantly between bituminous coal and anthracite coal fuels. The characteristic species of sources were phenanthrene, 9-fluorenone, and 2-nitrobiphenyl for biomass burning, and were phenanthrene, benzo[ghi]perylene, 1,4-naphthoquinone, and 2-nitrobiphenyl for coal combustion. The ratios of benzo [fluorantheneg benzo [b] fluoranthene + benzo [k]fluoranthene) were 0.40-0.45 for biomass burning and 0.89-0.91 for coal combustion, and these significantly different values constitute unique markers for distinguishing these fuels in source apportionment. Benzo[a]pyrene-equivalent factor emissions were 2.79-11.3 mg/kg for biomass and 7.49-41.9 mg/kg for coal, where parent PAHs contributed 92.0%-95.1% from biomass burning and 98.6%-98.8% from coal combustion. Total-PAH emissions from residential heating were 1552 t across Shaanxi province, to which wheat straw (445 t) in biomass burning and bituminous coal (438 t) in coal combustion were the highest contributors. Results from this study provide crucial knowledge for the source identification of PAHs as well as for the design of abatement strategies against pollutant emissions. (C) 2020 Elsevier Ltd. All rights reserved
Profiles and Source Apportionment of Nonmethane Volatile Organic Compounds in Winter and Summer in Xi'an, China, based on the Hybrid Environmental Receptor Model
No full textSummer and winter campaigns for the chemical compositions and sources of nonmethane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) were conducted in Xi'an. Data from 57 photochemical assessment monitoring stations for NMHCs and 20 OVOC species were analyzed. Significant seasonal differences were noted for total VOC (TVOC, NMHCs and OVOCs) concentrations and compositions. The campaign-average TVOC concentrations in winter (85.3 +/- 60.6 ppbv) were almost twice those in summer (47.2 +/- 31.6 ppbv). Alkanes and OVOCs were the most abundant category in winter and summer, respectively. NMHCs, but not OVOCs, had significantly higher levels on weekends than on weekdays. Total ozone formation potential was higher in summer than in winter (by 50%) because of the high concentrations of alkenes (particularly isoprene), high temperature, and high solar radiation levels in summer. The Hybrid Environmental Receptor Model (HERM) was used to conduct source apportionment for atmospheric TVOCs in winter and summer, with excellent accuracy. HERM demonstrated its suitability in a situation where only partial source profile data were available. The HERM results indicated significantly different seasonal source contributions to TVOCs in Xi'an. In particular, coal and biomass burning had contributions greater than half in winter (53.4%), whereas traffic sources were prevalent in summer (53.1%). This study's results highlight the need for targeted and adjustable VOC control measures that account for seasonal differences in Xi'an; such measures should target not only the severe problem with VOC pollution but also the problem of consequent secondary pollution (e.g., from ozone and secondary organic aerosols)
Effects of atmospheric aging processes on in vitro induced oxidative stress and chemical composition of biomass burning aerosols
No full textBiomass burning (BB) has an important impact on local/regional air quality and human health in China, but most previous studies overlooked the influence of atmospheric aging processes on cytotoxicity and chemical composition of BB aerosols. In this study, we combined a combustion chamber and an oxidation flow reactor to generate fresh and aged BB PM2.5. Human bronchial epithelial BEAS-2B cells were exposed to PM2.5 preparation for 24 h, and then determined for particle-induced reactive oxygen species (ROS) in vitro. The particle-induced ROS production increased by 11 %-64 % after two days of aging, suggesting an enhancement of in vitro-induced oxidative stress (OS) of aged BB particles. Chemical analysis showed that organic matter (OM) was the dominant component with no changes in relative abundance for the fresh and aged BB particles. Organic polycyclic aromatic compounds and some metals showed strong correlations with ROS in fresh particles, indicating the important effects of these harmful components on the OS of fresh BB aerosols. However, such correlations were not found for the aged particles, which is possibly related to the loss of non- or low-toxic semivolatile compounds and the formation of secondary harmful OM (such as some N-containing organic compounds) during the atmospheric aging processes