Changes In Layer Structure Research Articles

Theoretical investigations on exploring Si-based heterostructures with cubic and ground-state perovskites

First principles calculations in the framework of density functional theory (DFT) are performed to exploit replaceable perovskite oxides against the instability of traditional cubic SrTiO3 grown on silicon substrate. In this work, we consider more thermostable CaTiO3 and CaZrO3 with cubic and ground-state phase as the candidates to perform the gate dielectric. After the calibration of total energy and lattice transformation of ground-state perovskites to match with Si substrate, three categories of 2 × 2 heterostructures have been constructed and investigated through the geometrical change, atom displacement around interfacial layer, total energy and electronic structure change, under the variations on perovskite species, the concentration of interfacial layer and the thickness of perovskite film. And the results demonstrate that the category with half a monolayer of Ca/Sr atoms in interfacial layer and two unit-cell perovskite thicknesses show the type-I band alignment through their band alignment. Among this category, the heterostructure with Pnma CaZrO3 shows semiconductivity and excellent electrical property with larger band offset for the candidate of gate dielectric. This work provides a creative perspective to expand the perovskite diversity for the booming growth of integrated circuit technology.

Disentangling heterogeneous thermocatalytic formic acid dehydrogenation from an electrochemical perspective

Heterogeneous thermocatalysis of formic acid dehydrogenation by metals in solution is of great importance for chemical storage and production of hydrogen. Insightful understanding of the complicated formic acid dehydrogenation kinetics at the metal-solution interface is challenging and yet essential for the design of efficient heterogeneous formic acid dehydrogenation systems. In this work, formic acid dehydrogenation kinetics is initially studied from a perspective of electrochemistry by decoupling this reaction on Pd catalyst into two short-circuit half reactions, formic acid oxidation reaction and hydrogen evolution reaction and manipulating the electrical double layer impact from the solution side. The pH-dependences of formic acid dehydrogenation kinetics and the associated cation effect are attributed to the induced change of electric double layer structure and potential by means of electrochemical measurements involving kinetic isotope effect, in situ infrared spectroscopy as well as grand canonical quantum mechanics calculations. This work showcases how kinetic puzzles on some important heterogeneous catalytic reactions can be tackled by electrochemical theories and methodologies.

Tannin-on-protein adlayers: Secondary adsorption quantified by quartz crystal microbalance with dissipation monitoring (QCM-D)

The quartz crystal microbalance with dissipation monitoring (QCM-D) technique allows to detect adsorption and mechanical characteristics of protein adsorption layers at solid surfaces, including subsequent secondary adsorption of additional species interacting with the proteins. Here, we study the secondary adsorption of two different classes of tannins - hydrolysable vs. condensed - onto a β-lactoglobulin base layer using QCM-D in a protein/tannin adlayer configuration. Sequential flow experiments of protein solutions, tannin solutions and neat solvent or buffer are used to distinguish reversible from desorption-resistant layer formation, evaluate the viscoelastic characteristics the layers, and map protein/tannin interactions in view of their structural properties and origin. We find that for the majority of tannins, secondary layer structural changes (detected via a change in the dissipation factor) occur before significant mass adsorption (detected via the resonance frequency shift). In contrast, simultaneous onset of structural change and adsorbed mass within an observation window of 100 ms was only found for certain hydrolysable tannins. We use these data to build adsorption maps and group the tannins according to their adlayer properties, providing a physical basis for an improved understanding of the organoleptic perception of tannins and polyphenols, in particular with respect to attributes such as ‘astringency’ and ‘lingering’. Moreover, these maps provide insight into the capacity of different tannins to modify the mechanical properties of protein adsorption layers.

Understanding the Carbonation Phenomenon of C–S–H through Layer Structure Changes and Water Exchange

Understanding the Carbonation Phenomenon of C–S–H through Layer Structure Changes and Water Exchange

Single-cell and spatial transcriptomics analysis of human adrenal aging

ObjectiveThe human adrenal cortex comprises three functionally and structurally distinct layers that produce layer-specific steroid hormones. With aging, the human adrenal cortex undergoes functional and structural alteration or “adrenal aging”, leading to the unbalanced production of steroid hormones. Given the marked species differences in adrenal biology, the underlying mechanisms of human adrenal aging have not been sufficiently studied. This study was designed to elucidate the mechanisms linking the functional and structural alterations of the human adrenal cortex. MethodsWe conducted single-cell RNA sequencing and spatial transcriptomics analysis of the aged human adrenal cortex. ResultsThe data of this study suggest that the layer-specific alterations of multiple signaling pathways underlie the abnormal layered structure and layer-specific changes in steroidogenic cells. We also highlighted that macrophages mediate age-related adrenocortical cell inflammation and senescence. ConclusionsThis study is the first detailed analysis of the aged human adrenal cortex at single-cell resolution and helps to elucidate the mechanism of human adrenal aging, thereby leading to a better understanding of the pathophysiology of age-related disorders associated with adrenal aging.

Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate.

Molecular recognition and sensing can be coupled to interfacial capacitance changes on graphene foam surfaces linked to double layer effects and coupled to enhanced quantum capacitance. 3D graphene foam film electrodes (Gii-Sens; thickness approximately 40 μm; roughness factor approximately 100) immersed in aqueous buffer media exhibit an order of magnitude jump in electrochemical capacitance upon adsorption of a charged molecular receptor based on pyrene-appended boronic acids (here, 4-borono-1-(pyren-2-ylmethyl)pyridin-1-ium bromide, or abbreviated T1). This pyrene-appended pyridinium boronic acid receptor is employed here as a molecular receptor for lactate. In the presence of lactate and at pH 4.0 (after pH optimization), the electrochemical capacitance (determined by impedance spectroscopy) doubles again. Lactic acid binding is expressed with a Hillian binding constant (Klactate = 75 mol-1 dm3 and α = 0.8 in aqueous buffer, Klactate = 460 mol-1 dm3 and α = 0.8 in artificial sweat, and Klactate = 340 mol-1 dm3 and α = 0.65 in human serum). The result is a selective molecular probe response for lactic acid with LoD = 1.3, 1.4, and 1.8 mM in aqueous buffer media (pH 4.0), in artificial sweat (adjusted to pH 4.7), and in human serum (pH adjusted to 4.0), respectively. The role of the pyrene-appended boronic acid is discussed based on the double layer structure and quantum capacitance changes. In the future, this new type of molecular capacitance sensor could provide selective enzyme-free analysis without analyte consumption for a wider range of analytes and complex environments.

Inflammation-related pathology in the olfactory epithelium: its impact on the olfactory system in psychotic disorders.

Smell deficits and neurobiological changes in the olfactory bulb (OB) and olfactory epithelium (OE) have been observed in schizophrenia and related disorders. The OE is the most peripheral olfactory system located outside the cranium, and is connected with the brain via direct neuronal projections to the OB. Nevertheless, it is unknown whether and how a disturbance of the OE affects the OB in schizophrenia and related disorders. Addressing this gap would be the first step in studying the impact of OE pathology in the disease pathophysiology in the brain. In this cross-species study, we observed that chronic, local OE inflammation with a set of upregulated genes in an inducible olfactory inflammation (IOI) mouse model led to a volume reduction, layer structure changes, and alterations of neuron functionality in the OB. Furthermore, IOI model also displayed behavioral deficits relevant to negative symptoms (avolition) in parallel to smell deficits. In first episode psychosis (FEP) patients, we observed a significant alteration in immune/inflammation-related molecular signatures in olfactory neuronal cells (ONCs) enriched from biopsied OE and a significant reduction in the OB volume, compared with those of healthy controls (HC). The increased expression of immune/inflammation-related molecules in ONCs was significantly correlated to the OB volume reduction in FEP patients, but no correlation was found in HCs. Moreover, the increased expression of human orthologues of the IOI genes in ONCs was significantly correlated with the OB volume reduction in FEP, but not in HCs. Together, our study implies a potential mechanism of the OE-OB pathology in patients with psychotic disorders (schizophrenia and related disorders). We hope that this mechanism may have a cross-disease implication, including COVID-19-elicited mental conditions that include smell deficits.

NiTi-Layered Double Hydroxide@Carbon Nanotube as a Cathode Material for Chloride-Ion Batteries.

Chloride-ion batteries (CIBs) are one of the promising candidates for energy storage due to their low cost, high theoretical energy density and high safety. However, the limited types of cathode materials in CIBs have hindered their development. In this work, a NiTi-LDH@CNT composite is prepared using a reverse microemulsion method and applied in CIBs for the first time. The specific surface area and the pore volume of the obtained NiTi-LDH@CNT composites can reach 266 m2 g-1 and 0.42 cm3 g-1, respectively. Electrochemical tests indicate that the composite electrode delivers a reversible specific capacity of 69 mAh g-1 after 150 cycles at a current density of 100 mA g-1 in 0.5 M PP14Cl/PC electrolyte. Ni2+/Ni3+ and Ti3+/Ti4+ valence changes during electrochemical cycling are demonstrated by X-ray photoelectron spectroscopy (XPS), while reversible migration of Cl- is revealed by ex-situ EDS and ex-situ XRD. The stable layered structure and abundant valence changes of the NiTi-LDH@CNT composite make it an exceptional candidate as a cathode material for CIBs.

Arctic Sea Ice Causes Seasonal Differences in the Response of Arctic Water Vapor to Climate Warming in the CMIP6 Model, HadGEM3‐GC3.1

AbstractWater vapor in the Arctic can be attributed to local evaporation and transport from mid‐latitudes. Here we investigate the response of Arctic water vapor to declining sea ice in a climate model, using an idealized warming scenario in which the Arctic becomes ice free year‐round. We find distinct monthly patterns in water vapor change with warming, with a strong influence of sea ice loss on changes to evaporation, except in summer when transports dominate. Before the Arctic becomes ice‐free, total column water increases at a rate slower than that indicated by the Clausius‐Clapeyron relationship; once ice‐free, total column water increases at a rate equal to Clausius‐Clapeyron. The exception is summer when the increase is initially faster then becomes slower when ice‐free. The boundary layer structure changes, under global warming, from stratified to well mixed in all seasons except summer, which remains largely unchanged throughout the ice‐free transition.

Dynamic evaluation of pathological changes in a mouse acne model by optical imaging technology.

Acne vulgaris is a disorder of the pilosebaceous unit that is primarily caused by hyperseborrhoea, colonization with Propionibacterium acnes, hyperkeratosis and an inflammatory response. Existing pharmacodynamic assessment methods primarily focus on a single causative factor at a certain time point, making it difficult to assess multiple factors simultaneously in real time. Therefore, it is crucial to establish a dynamic and nondestructive method for the assessment of acne in vivo. This study utilized four-dimensional optical imaging techniques to assess the pathogenic factors and pathological progression of acne. LSCI was employed to measure blood flow; TPEF was used to observe inflammatory changes (NAD(P)H) in epidermal granular layer cells and structural changes in collagen fibres in the dermal layer. Additionally, the dermatoscope was used to investigate the micro-characterization of the lesions. We observed that the epidermis in the lesion area was thickened, hair follicles were keratinized, and there was obvious inflammation and blood flow aggregation by optical imaging technology. Based on these findings, the pathological progression of this acne model could be divided into the inflammation phase, accompanied by bacterial colonization, and the reparative phase. These results provide a new perspective for the assessment of acne and offer an experimental basis for the selection of precise drugs for clinical use.

Optical coherence tomography as retinal imaging biomarker of neuroinflammation/neurodegeneration in systemic disorders in adults and children.

The retina and the optic nerve are considered extensions of the central nervous system (CNS) and thus can serve as the window for evaluation of CNS disorders. Spectral domain optical coherence tomography (OCT) allows for detailed evaluation of the retina and the optic nerve. OCT can non-invasively document changes in single retina layer thickness and structure due to neuronal and retinal glial cells (RGC) modifications in systemic and local inflammatory and neurodegenerative diseases. These can include evaluation of retinal nerve fibre layer and ganglion cell complex, hyper-reflective retinal spots (HRS, sign of activated microglial cells in the retina), subfoveal neuroretinal detachment, disorganization of the inner retinal layers (DRIL), thickness and integrity of the outer retinal layers and choroidal thickness. This review paper will report the most recent data on the use of OCT as a non invasive imaging biomarker for evaluation of the most common systemic neuroinflammatory and neurodegenerative/neurocognitive disorders in the adults and in paediatric population. In the adult population the main focus will be on diabetes mellitus, multiple sclerosis, optic neuromyelitis, neuromyelitis optica spectrum disorders, longitudinal extensive transverse myelitis, Alzheimer and Parkinson diseases, Amyotrophic lateral sclerosis, Huntington’s disease and schizophrenia. In the paediatric population, demyelinating diseases, lysosomal storage diseases, Nieman Pick type C disease, hypoxic ischaemic encephalopathy, human immunodeficiency virus, leukodystrophies spinocerebellar ataxia will be addressed.

Diagnosis of ulcerative colitis and Crohn's disease using transabdominal ultrasonography.

The following are some common features of ulcerative colitis (UC) and Crohn's disease (CD) on transabdominal ultrasonography (TUS). UC, which consists primarily of mucosal inflammation, is seen on TUS as wall thickening with preserved layer structure continuing from the rectum in the active phase of UC. Inflammation confined to the mucosa is seen as thickening of the mucosal/submucosal layers. When the inflammation becomes severe, the echogenicity of the submucosal layer decreases and the layer structure becomes indistinct. CD, which consists primarily of discontinuous transmural inflammation, shows more pronounced hypoechoic wall thickening than UC at the transmural inflammation. On TUS, the layer structure becomes indistinct and gradually disappears due to the depth of the myriad inflammation during the active phase of CD. It is important to evaluate the changes in wall thickening and layer structure when diagnosing UC and CD with TUS. In addition, diagnostic techniques such as color Doppler and contrast-enhanced ultrasonography, which can be used to assess blood flow, and elastography, which can be used to evaluate stiffness, are also used. Thus, TUS is a noninvasive and convenient modality that shows promise as a useful examination for diagnosis of UC and CD.

Morphologic and Morphometric Evaluation of the Carotid Artery Wall: A Cadaver-Based Light and Scanning Electron Microscopic Study

Introduction: A variety of changes occur on the elastic artery wall with age. Ultrastructural studies made in this area are mostly animal based. We aimed to evaluate wall changes and three-dimensional organization of the elastic lamellae with aging in humans. Material and Methods: Common carotid arteries were obtained from 17 human cadavers which were grouped as G1 (n = 6), 30–39 years; G2 (n = 5), 40–49 years; and G3 (n = 6), >50 years of age. Samples were evaluated under light and scanning electron microscopes. Results: Examination of G1 revealed intimal thickening and foamy cell infiltration. G2 and G3 had plaques bulging into the lumen and interlamellar space was widened. The lamellae were more straight. There was a positive correlation between intimal thickness and age. Elastic fiber content decreased with aging. Scanning electron microscopic analysis confirmed the findings. G1 and G2 had a smooth surfaced internal elastic lamina with uniform fenestrations whereas G3 contained numerous irregular fenestrae. Discussion and Conclusion: With this study, we showed some other wall structure changes beside plaque formation by aging. Which layer is affected the most was not clear at previous clinical studies because using ultrasonography (USG) cannot address the layer. Microscopic evaluation of this study revealed that when a wall thickening is detected by USG, it is due to intimal thickening. The specific vessel layer structural changes are important for proper treatment.

Synergistically Enhanced Electrochemical Properties of LiNi0.5Co0.2Mn0.3O2 by the Co-Modification of Ti and Na

The layered material of nickel cobalt manganese oxide lithium oxide is one of the most promising lithium-ion battery (LIBs) materials, with the characteristics of high capacity and high density. However, most nickel-rich layered oxides have the phenomenon of cation mixing and the phenomenon that the layered structure changes to the spinel structure during the cycle, which results in poor capacity and cycle performance under high cut-off voltage. Herein, we modified LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 with Ti and Na co-doping to observe the changes in the specific capacity, cycle performance and crystal structure of the material. Ti and Na co-doped LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 has the most obvious effect on increasing the discharge specific capacity and improving the cycle performance. In sthe voltage range of 3–4.5[Formula: see text]V, its discharge specific capacity reaches 183.5[Formula: see text]mAh/gat 0.5C, and the capacity retention rate after 100 cycles is 81.96%, and its discharge specific capacity reaches 164.2[Formula: see text]mAh/g at 1C and after 100 cycles Capacity retention rate is 80.93%. The introduction of Ti and Na plays an important role in improving the cation mixing phenomenon and improving the stability of the crystal structure.

The Theoretical Description for a Sucralose Electrochemical Cathodical Determination over a 9-9´-Diacridyl-modified Electrode

A novel electroanalytical process for sucralose determination has been theoretically suggested. Sucralose is immobilized over an acridine derivative 9-9´-diacridyl, yielding a quaternary salt, which is thereby gradually electrochemically reduced to an N-N´-disubstituted acridone derivative. The correspondent mathematical model has been developed and analyzed by means of linear stability theory and bifurcation analysis, and this analysis has shown the high probability of the oscillatory and monotonic instabilities, due to the double electric layer structure changes during all of the stages of the process. Nevertheless, it also confirms the efficiency of 9-9´-diacridyl-modified electrode for sucralose determination in an electroanalytical system, which may be coupled with a fluorescent indicator. DOI: http://dx.doi.org/10.17807/orbital.v13i3.1584

Synchrotron X-Ray Tomography Investigation of Fundamental Degradation Mechanisms in Polymer Electrolyte Membrane Water Electrolyzers

Electrochemical energy conversion devices such as fuel cells and electrolyzers provide the potential to meet global energy demands, particularly as a renewable alternative to fossil fuels or as part of a more environmentally friendly combination. In both polymer electrolyte membrane (PEM) fuel cells (PEMFCs) and water electrolyzers (PEMWEs), degradation studies are extremely important. Degradation mechanisms will become even more problematic as electrolyzers transition towards intermittent operation; additionally, there is a need to reduce noble metal loadings, used to combat slow kinetics of the anodic oxygen evolution reaction (OER), to meet cost goals at scale.1,2 A shift towards scalable, efficient low-loading catalyst layers operated with intermittent power will lead to significant degradation concerns, but the extent and severity are not yet fully understood.2–4 Advanced physicochemical characterization techniques are required to interpret electrochemical data and fully understand how the device components degrade. Synchrotron X-ray based tomography and spectroscopy techniques in particular can provide sensitive analysis of chemical states, elemental distribution, and visual information to elucidate large-scale changes in catalyst layer (CL) chemistry, morphology, and structure after relevant testing protocols. These methods are highly complementary to lab-based characterization methods, such as electron microscopy and X-ray spectroscopy.In this study, commercial Ir and IrO2 black catalysts were obtained and studied as catalyst powders, fresh catalyst-coated membranes (CCMs), and tested CCMs. Electrochemical durability testing was performed on PEMWEs to replicate either the start-up/shut-down process (intermittent operation) or an extended hold (steady-state operation). Transmission X-ray microscopy (TXM) was used to visualize distribution and morphology of iridium throughout the CL, as well as CL porosity. By collecting microscopy images while scanning the X-ray energy across the Ir absorption edge, X-ray absorption near-edge structure (XANES) chemical maps were generated to track iridium oxidation state to compare Ir and IrO2 CLs as well as the impact of testing. These synchrotron methods were supplemented with electron microscopy of the CCM surface as well as cross-sectional analysis to investigate changes in morphology, structure, and elemental distribution, and surface-sensitive X-ray photoelectron spectroscopy (XPS) to track relevant surface species after testing. Together, these techniques provide an unparalleled look into degradation of PEMWE catalyst layers at multiple scales to isolate the impact of individual CL constituents on overall electrode structure and stability.(1) Ayers, K. E. Curr. Opin. Electrochem. 2019, 18, 9–15.(2) Alia, S. M.; Stariha, S.; Borup, R. L. J. Electrochem. Soc. 2019, 166 (15), F1164–F1172.(3) Ayers, K. E.; Danilovic, N.; Ouimet, R.; Carmo, M.; Pivovar, B. S. Annu. Rev. Chem. Biomol. Eng. 2019, 10, 219–239.(4) Ayers, K. E.; Renner, J. N.; Danilovic, N.; Wang, J. X.; Zhang, Y.; Maric, R.; Yu, H.

Research of the polyethylene packaging layer structure change in contact with a food product at exposure to ultraviolet radiation

The sanitary and hygienic safety of modern packaging is determined by the layer of packaging material in direct contact with the food product. This layer in most cases is a synthetic polymer of the polyolefin class — low density polyethylene. This material is used as a stand-alone packaging and in multilayer and combined packaging materials. During thermal and photooxidation, compounds can form in it that negatively affect the safety of the package, which can migrate into the product. Food technologies use methods of disinfecting packaging materials and packaging before filling or bottling products. These methods include ultraviolet irradiation of the surface, which has a bactericidal effect. Using spectral methods of analysis, researches have been carried out on changes in the polyethylene layers structure in the film’s composition, multilayer films and combined packaging materials when exposed to pulsed ultraviolet radiation in a wide spectral range (irradiation with a pulsed xenon lamp). Deformations of polyethylene macromolecules chemical bonds on the surface and boundary layers under the influence of pulsed UV-irradiation have been revealed. The IR spectra of ATR (Attenuated Total Reflection) were obtained, the analysis of which showed that the monofilm is subject to the greatest destructive effect, as evidenced by the appearance of characteristic absorption bands responsible for the formation of aldehyde, ketone groups, as well as for the polymer chain termination. It is shown that the use of food soot in the composition of multilayer packaging films blocks their photo destruction. Upon irradiation of a combined material based on cardboard intended for bottling milk, an absorption band was found in the spectra, which is responsible for the onset of the destruction process with the formation of aldehyde and carboxylate groups with the formation of aldehyde and carboxylate groups.Comparison of changes in structure in three different packaging objects containing a polyethylene layer shows the feasibility and necessity of using combined and multilayer materials for food products packaging, in which, even under extreme UV-irradiation, there are practically no photo destruction processes, which is confirmed by spectral researches.

Effect of fiber content on the layer structure formation of fibers inside injection-molded products using short glass fiber-reinforced materials

Abstract This study aims to clarify the relationship between the layer structure transition of fibers caused by the change in the flow field and the thermal properties and fiber interaction when the glass fiber content is changed. Polyamide 6 samples with different short glass fiber contents were prepared, and changes in layer structure during the flow process of injection molding were compared using X-ray computed tomography. An injection-molding simulation was performed to compare the changes in the layer structure of fibers during the flow process, and the temperature distribution and shear rate distribution were obtained by numerical analysis. Furthermore, the effect of fiber interaction on the layer structure transition of fibers was considered using a relaxation function composed of the fiber content, fiber shape factor, and strain rate.

Effects of a broadleaf-oriented transformation of coniferous plantations on the hydrological characteristics of litter layers in subtropical China

As a unique structural level of forest ecosystems, the litter layer has significant ecological effects on soil and water conservation. The broadleaf-oriented transformation of coniferous forests is an effective approach for reducing the degradation of the ecosystem services of subtropical coniferous plantations, but previous studies rarely involved the effects of the change in litter layer structure and ecological hydrology caused by the construction of mixed coniferous and broad-leaved forests. In our study, the litter and hydrological characteristics of 5 kinds of mixed coniferous and broadleaf forests (15 years after their transformation) and nontransformed coniferous plantations at the Longli National Forest Farm, China were studied quantitatively through in situ surveys and laboratory experiments. Compared with the coniferous plantation, the thickness and quantity of undecomposed layer in mixed coniferous and broad-leaved forests ranged from −21.86% ~ 46.05% and −44.91% ~ −18.91%, while that of semidecomposed layer ranged from 82.61% ~ 136.23% and 11.75% ~ 63.49%. A logarithmic function and an exponential function fit the water holding ratio and water absorption rate of the litter very well. The maximum water-holding capacity and effective storage capacity of the litter in all the forest types are both greater in the undecomposed layer than in the semidecomposed layer. The introduction of Michelia maudiae Dunn and Bretschneidera sinensis Hemsl into coniferous Pinus massoniana plantations can significantly increase the effective litter water retention capacity, but the introduction of Camellia oleifera Abel will be counterproductive. Leaves are the most important component of litter and provide the most runoff retention. The leaf area increased by 0.01 m3 on average, and the maximum water capacity increased by 1.68 g/g on average. The density of different plant organs in the litter was as follows: leaf < fruit < branch; the density increased by 0.1 g/cm3 on average, and the maximum water capacity decreased by 0.29 g/g on average. Overall, Michelia maudiae Dunn (Magnoliaceae) and Bretschneidera sinensis Hemsl (Bretschneideraceae) are more suitable than other broad-leaved species for the transformation of subtropical coniferous plantations. We suggest that forest resource managers should take into account the impact of tree species differences on the ecological hydrology of plantations when making management decisions.

The dominant mechanism of the explosive rise of PM2.5 after significant pollution emissions reduction in Beijing from 2017 to the COVID-19 pandemic in 2020

The Chinese government implemented strict emission reduction measures of air pollution between 2013 and 2017. However, from the winter of 2017 until February 2020, during the COVID-19 pandemic, the twenty explosive rise (ER) events of PM2.5 mass in twelve heavy aerosol pollution episodes (HPEs) still appeared in Beijing and its vicinity (BIV). To explore the controlling mechanism for the ER under the condition of drastically reduced emissions, the vertical structure of meteorological elements by L-band second-level sounding and aerosol properties by Lidar were investigated associating with the analysis of surface concentration in PM2.5 mass, its main precursor gases, as well as black carbon (BC) by seven-wavelength Aethalometer. The planetary boundary layer height (BLH) was also estimated together with an analysis of the unfavorable meteorological index (PLAM) that can quantify the impact of unfavorable meteorological conditions to cause the change of PM2.5 concentration. The results suggested that the ER reoccurrence's fundamental cause is that the emissions have not yet fallen sufficiently to a level to decouple HPEs from unfavorable meteorological conditions. During the ER period, the BLH dropped significantly. The fact that PM2.5, its precursor gases, and black carbon increased almost in a similar proportion, indicating that the boundary layer structure change caused by aerosol accumulation is the dominant reason for the ER phenomenon compared to the chemical conversion factor. The two-way feedback effect between the further worsened meteorological conditions and the accumulation of PM2.5 typically interpreted 54%–93% of the ER. An HPE starting 8 Feb. 2020 during the COVID-19 period underwent one of the worst meteorological conditions, quantified by PLAM, in BIV since 2013. However, with a similar level of unfavorable meteorological conditions, the average PM2.5 concentration during the HPE in 2020 was only about 66% of that of a similar HPE in 2016. It shows that the substantial reduction of emissions reduces the PM2.5 pollution level primarily as before when facing an equivalent level of unfavorable meteorological conditions. These results combined suggest that China's continuous efforts to reduce emissions proceed in the right direction and have achieved the desired results.