Institute of Earth Environment
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Seasonality of precipitation recorded in a modern (1907-2008) annually laminated stalagmite from central China
No full textSeasonality of precipitation in the Asian monsoon region has significant impacts on social and economic development. Here, we analyzed a seasonally resolved delta O-18 series of an annually laminated stalagmite from Xianglong Cave to assess its potential as a proxy for seasonal precipitation. The delta O-18 values reveal fabric-correlated annual cycles, with lower delta O-18 values occurring in the white porous layer (WPL) during summer monsoon (SM) season, whereas higher values occurring in the dark compacted layer (DCL) during non-summer monsoon (NSM) season. We calculated the seasonal amplitude of delta O-18 (Delta O-18) using the highest value minus the lowest value in an annual cycle. Comparisons suggest that the A Delta O-18 series can record precipitation seasonality, with lower Delta O-18 values corresponding to increased SM/NSM rainfall ratios and higher values corresponding to reduced SM/NSM rainfall ratios. Our reconstruction suggests increased precipitation seasonality contrast (i.e., increasing SM/NSM rainfall ratio with more SM rainfall and/or less NSM rainfall) during 1914-1919, 1935-1942, 1958-1962, 1979-1985, and 1999-2005 (A.D.), with a probably 27-year cycle. The seasonality of precipitation in central China correlates well with the Pacific Decadal Oscillation (PDO) on a decadal scale. Increased SM/NSM rainfall ratio was observed during the warm phase of PDO, and decreased SM/NSM rainfall ratio was observed during the cold phase of PDO
Chemical Composition of Gas and Particle Phase Products of Toluene Photooxidation Reaction under High OH Exposure Condition
No full textIn the current study, the photooxidation reaction of toluene (C7H8) was investigated in a Potential Aerosol Mass Oxidation Flow Reactor (PAM OFR). The hydroxyl radical (OH) exposure of toluene in the PAM OFR ranged from 0.4 to 1.4 x 10(12) molec cm(-3) s, which is equivalent to 3 to 12 days of atmospheric oxidation. A proton transfer reaction-mass spectrometer (PTR-MS) and a scanning mobility particle sizer (SMPS) were used to study the gas-phase products formed and particle number changes of the oxidation reaction in PAM OFR. The secondary organic aerosol (SOA) formed in the PAM OFR was also collected for off-line chemical analysis. Key gas-phase reaction products of toluene, including glyoxal, methyl glyoxal, unsaturated carbonyl compounds, and benzaldehyde, were identified by the PTR-MS. Second generation products, including acetic acid, formaldehyde, formic acid, and acetaldehyde, were also detected. By comparing the mass spectrums obtained under different OH exposures and relative humidity (RH), changes in the two parameters have minimal effects on the composition of gas-phase products formed, expect for the spectrum obtained at OH exposure of 0.4 x 10(12) cm(-3) s and RH = 17%, which is slightly different from other spectrums. SMPS results showed that particle mass concentration increases with increasing OH exposure, while particle number concentration first increases and then decreases with increasing OH exposure. This result probably suggests the formation of oligomers at high OH exposure conditions. Off-line chemical analysis of the SOA sample was dominated by C4 diacids, including malic acid, citramalic acid, and tartaric acid. The well-known toluene SOA marker 2,3-Dihydroxy-4-oxopentanoic acid, as well as 2,3-dihydroxyglutaric acid, which has not been identified in previous toluene photooxidation experiments, were also detected in the SOA sample. Our results showed good agreements with the results of previous smog chamber studies of toluene photooxidation reaction, and they suggested that using PAM OFR for studies of oxidation reaction of different VOCs can be atmospherically relevant
Stable Isotopes Reveal Water Vapor Sources of Precipitation over the Jiaolai Plain, Shandong Peninsula, China
No full textA prerequisite for using isotopic techniques to study the regional water cycle of a mountainous area is to examine the stable isotopic composition of precipitation. These findings are of great significance for an in-depth understanding of water cycle processes. In this study, each precipitation event was sampled and used to investigate the characteristics of stable hydrogen and oxygen isotopes in precipitation over the Jiaolai Plain and its surrounding areas. NCEP/NCAR data was used for the wind speed and direction, relative humidity, and precipitable amount in the study area during the sampling period. The water vapor sources of the precipitation over the plain were revealed through a comparative analysis of seasonal variations in precipitation isotopes between Global Network of Isotopes in Precipitation stations located along different vapor transport paths. The results showed that the local meteoric water line was delta H-2 = 6.38 delta O-18 + 0.72, with a gradient of less than 8. This indicates that the precipitation process was affected by non-equilibrium evaporation occurring when the drops fell below the cloud base. Temperature and amount effects were observed in the delta O-18 of the precipitation, although the altitude effect was not significant. The water vapor source of the precipitation was predominantly controlled by the East Asian Monsoon from June to September, with the primary source being evaporation from the adjacent Pacific Ocean. The plain was controlled by the Westerlies from October through May, with the predominant vapor source being local evaporation. Water vapor from the polar region had a minimal impact. These findings can serve as the basis for studying surface water-groundwater-seawater transformations
Revealing DeNOx and DeVOC Reactions via the Study of the Surface and Bandstructure of ZnSn(OH)(6) Photocatalysts
No full textPhotocatalytic materials present a robust approach in tackling pollutants in the air. However, the involving reactions and their associated toxicity, those are important for practical implications, have not been sufficiently reported. Here, we synthesize ZnSn(OH)(6) and control its morphology by changing NaOH's dosage in a one-step hydrothermal growth. Combining results from density functional theory and experimentation, we initiatively show the roles of exposed facets, oxygen defects, metal terminated surface, and bandstructure of ZnSn(OH)(6). By carefully characterizing reactions during DeNOx and DeVOC processes, this work enables a comprehensive understanding of photocatalytic activity against pollution of nitric oxide and VOCs. Also, a new systematic calculation of the apparent DeNOx index is introduced for evaluating the total toxicity. The trapping experiments reveal a balance in the involvement of e(-), h(+), center dot OH radicals in the photocatalytic DeNOx and DeVOC. Thus, our findings would enable an important understanding of addressing air pollution using high-performance photocatalysts and proper evaluation of total toxicity. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Seasonal/Interannual Variation and Controlling Factors for Oxygen and Carbon Isotopes of Ostracod Shells Collected From a Time-Series Sediment Trap in Lake Qinghai
No full textBecause the shell substance of an ostracod is derived entirely from the water body where it lives, its chemical compositions are sensitive to aquatic environment and thus have been used to reconstruct past climatic and environmental changes. However, there is controversy about the controlling factors for the different compositions of ostracod shells from various water bodies. In this study, seasonal and interannual variations in daily flux and stable oxygen-carbon isotopic compositions (delta O-18, delta C-13) for two species of ostracod shells (Limnocythere inopinata and Eucypris mareotica) and their controlling factors are discussed, based on ostracod shell samples collected from a time-series sediment trap from July 2010 through September 2012 and from surface sediments in Lake Qinghai, which were correlated with the state-of-the-art sensing data of the lake water. The results show that the daily flux of L. inopinata shells is an order of magnitude higher than that of E. mareotica. The delta O-18 and delta C-13 of both L. inopinata and E. mareotica shells have distinctly interannual and seasonal variations, with species differences. Interannual differences of delta O-18 for the two species of ostracod shells directly reflect the systematic differences of the summer water temperature between 2010 and 2012. We propose that seasonal variations of both delta O-18 and delta C-13 for the two species are affected by the precipitation of authigenic carbonates in microenvironment induced by high water temperature in summers, highlighting their environmental implications in Lake Qinghai
The Roles of N, S, and O in Molecular Absorption Features of Brown Carbon in PM2.5 in a Typical Semi-Arid Megacity in Northwestern China
No full textBrown Carbon (BrC) absorbs light in wavelength of 300-400 nm, and BrC molecule (BrCM) is a fundamental component responsible for aerosol radiative forcing. In this study, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with electrospray ionization (ESI) was used to determine methanol extracted BrCM in PM2.5 collected in Xi'an, China. The absorption of individual BrCM was quantified through partial least square regression (PLSR) method. Results showed that 77.5% and 91.8% of winter and summer BrCMs were weak absorptive. The top BrCMs were responsible for 60.4% and 84.6%, respectively, of the absorbances in summer and winter. The nitrogen (N)-containing organic molecules were identified to be critical components of light-absorbing matters in both of the two seasons, outlining the significance of N chromogenesis in BrC. The top BrCMs were more closely related to -(O)NO2 that originated from NO2 engaged reactions in winter, and to -NH that formed in NH3 reactions in summer. Sulfur (S)-containing functional groups were not chromophoric while sulfur dioxide (SO2) triggered N-containing and S-free BrCM formations under high nitrogen oxides (NOx) concentration levels and relative humidity (RH) in winter. Hypochromicity of oxygen (O) in BrC was discovered because of the photobleaching of oxidation and weak light-absorbing of highly oxidized molecules
Stoichiometric models of microbial metabolic limitation in soil systems
No full textAim Ecoenzymatic stoichiometry provides a promising avenue for deciphering resource constraints on soil microbial metabolism but is hampered by limitations in current modelling techniques. Innovation Herein we developed new models for quantifying microbial metabolic limitations based on the stoichiometric and metabolic theories of ecology, using an extensive database (n = 2,667) that revealed relationships far from the widely recognized mean ratio of 1:1:1 for carbon : nitrogen : phosphorus (C : N : P) acquiring enzyme activities. We estimated the balance points of P and N acquisition (x(0), y(0)) in the absence of resource constraints to redefine the boundary between P versus N limitation. We then calculated two alternative boundary conditions defining P versus N limitation by scaling the classic threshold element ratio (TER), generating two new models (TEREEA and TERL). In addition, a new enzyme vector (V-T) model was devised by correcting traditional vector calculations based on observed enzyme activities against these balance points. Main conclusions These three new models more consistently predicted microbial metabolic limitations than the traditional TER and vector models. They also predicted that microbial metabolism in high-latitude grasslands and low-latitude forests were predominantly limited by soil N and P, respectively, and that increases in soil organic C with ecosystem development could intensify these limitations. In contrast, fertilizers alleviated these limitations in agricultural ecosystems, suggesting that widespread anthropogenic effects could potentially alter microbial resource limitations even in natural ecosystems. In addition, C limitation to microbial metabolism identified by the new V-T model showed a consistent negative correlation with microbial C use efficiency among ecosystems, confirming that resource constraints regulate microbial resource allocation. These new models provide more precise predictions of microbial metabolic limitations across a wide range of ecosystems and thus may be useful tools for the study of microbial macroecology
Oxidative stress-inducing effects of various urban PM2.5 road dust on human lung epithelial cells among 10 Chinese megacities
No full textPM2.5 Road dust samples were collected from 10 representative cities in southern and northern China for examination of chemical components and oxidative stress levels in A549 cells. Downtown road dust was abundance of heavy metals, EC and PAHs compared to nondowntown road dust. Source apportionment also revealed the relative higher contribution of vehicle emission to downtown (35.8%) than nondowntown road dust (25.5%). Consequently, downtown road dust induced much higher intracellular reactive oxidative species (ROS) levels than that from nondowntown (p < 0.05). This study highlights that the ROS-inducing capacity of road dust in China is lower at lower latitudes, which resulted in a significantly higher ROS-inducing capacity of road dust from northern cities than southern ones. Hotspot analysis demonstrated that heavy metals (i.e., Cr, Zn, Cu and Pb) in road dust were the most closely associated with ROS production in A549 cells. Vehicle emission and combustion emission in road dust were identified to be correlated with cellular ROS production. The findings highlight the ROS-inducing effect of PM2.5 road dust and also serve as a reference to make the targeted solutions for urban road dust pollution control, especially from a public health perspective
Important contribution of N2O5 hydrolysis to the daytime nitrate in Xi' an, China during haze periods: Isotopic analysis and WRF-Chem model simulation
No full textNitrate, as one of the major components of tropospheric aerosols, plays a crucial role in winter haze formation. While, the formation mechanism of the high production of nitrate in Chinese megacities is still not fully understood. To quantify the contributions of major formation pathways to nitrate, airborne particles in Xi'an, inland China during the winter of 2017 were measured and analyzed for the water-soluble ions and stable nitrogen/oxygen isotope compositions of nitrate in PM2.5, followed by a WRF-Chem model simulation. The oxygen isotopic results indicated that N2O5 hydrolysis was an important formation pathway for the daytime nitrate in the haze episodes. The model simulation further revealed that N2O5 hydrolysis contribution increased from 8.2% to 20.5% of the total nitrate over 14:00-16:00 p.m., clearly showing that N2O5 formation followed by a heterogeneous hydrolysis to nitrate can effectively proceed in daytime under the abundantly co-existing O-3, NO2 and NH3 conditions
Achieving rapid response and high sensitivity in ethanol gas sensing using a Pt/W18O49 ohmic contact via modulating the adsorption and activation properties: Theoretical and experimental insights
No full textIn this work, Pt nanoparticles-decorated urchin-like W18O49 microspheres are synthesized by a simple hydrothermal-photodeposition method, and the effect of a contact created between Pt nanoparticles and W18O49 nanorods on response, sensitivity, detection limit, and recovery time in ethanol gas sensing is explored. Transmission electron microscopy (TEM) results confirm the successful deposition of Pt nanoparticles with a size of 5-10 nm on the W18O49 nanorods. The deposition of Pt nanoparticles on the surface of W18O49 nanorods significantly enhances a gas-sensing performance for 10 ppm ethanol at 300 degrees C (with a response value of 22). Compared to the W18O49 sensor, the Pt/W18O49 sensor exhibits faster response-recovery time, lower detection limit, higher response value, and excellent selectivity for detection of ethanol gas. Furthermore, the Pt/W18O49 sensor also shows a fast response-recovery time of 28.5 s and 14.3 s toward 200 ppb ethanol. The results from gas chromatography demonstrate a significant difference between Pt/W18O49 and W18O49 sensors in the efficiency of ethanol conversion to CO2. The interface electron-transfer mechanism between the Pt and W18O49 is further studied by density functional theory (DFT) calculations, providing theoretical insights into the adsorption energy and activation ability of Pt/W18O49 and W18O49 for oxygen and ethanol molecules. The DFT results reveal that an Ohmic contact is formed at the Pt/W18O49 interfaces, indicating the enhanced ability of electron transfer and increased activation of gas molecules. Moreover, the influence of the Ohmic contact on the enhancement of the ethanol gas sensing performance is discussed via electron depletion theory. This study demonstrates a superior performance of Pt-modified W18O49 in ethanol gas detection with theoretical and experimental insights into the mechanism for enhanced ethanol gas sensing