High Atmospheric Research Articles

Delayed Impact of Biomass Burning in the Indochinese Peninsula on the Bay of Bengal Monsoon

Abstract The Indochinese Peninsula experiences a dry season with extensive biomass burning peaking from March to April. As the monsoon arrives, rainfall significantly removes aerosols through deposition, ending the emission season. However, the biomass burning aerosols exert an influence on the atmospheric circulation prior to the monsoon onset. This study employed statistical methods and a regional atmosphere–chemistry model [WRF Model coupled with chemistry (WRF-Chem)] to investigate the delayed impact of biomass burning from the Indochinese Peninsula on the monsoon onset. The results indicate that the cold sea surface temperature anomaly caused by the aerosols during the emission season can be stored in the ocean and inhibit convective activities over the adjacent sea regions in the postemission season, suppressing the southwestward cross-equatorial flow over the southern Bay of Bengal. This suppression delays the westward extension and northward shift of the upper-level South Asian high pressure system, along with its divergence and subsidence effects, thereby postponing the breakdown and retreat of the subtropical high-pressure belt. Simultaneously, the cold sea temperature also suppresses the development of a warm pool in the southeastern Bay of Bengal, which is associated with the generation of a monsoon onset vortex. Consequently, the onset of the Bay of Bengal monsoon is delayed. Due to the decreasing delayed effects of aerosols over time and the counteractive warming from the accelerated abnormal anticyclonic circulation in the upper-level Bay of Bengal, which results in accelerated disappearance of the cold signal in sea surface, the delayed influence of aerosols diminishes gradually after the onset of the Bay of Bengal monsoon until it disappears. Significance Statement This study explores the correlation between spring biomass burning in the Indochinese Peninsula and the onset of the Bay of Bengal and South China Sea monsoons. The research reveals that biomass burning during the emission season might postpone the initiation of the Bay of Bengal monsoon, while it has minimal influence on the South China Sea monsoon. By employing sensitivity experiments using models, the study elucidates the underlying mechanisms responsible for these observed effects.

Fe3O4‐doped highly electromagnetically shielded PAN‐PVP composite porous carbon films

AbstractWith the wide application of modern electronic devices, the problem of electromagnetic pollution is becoming more and more serious, and the demand for efficient electromagnetic shielding materials is becoming more and more urgent. To address this problem, we homogeneously mixed polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), and triiron tetraoxide (Fe3O4) nanoparticles by solution blending, and prepared composite precursor membranes by taking advantage of the magnetic properties and good electromagnetic loss characteristics of Fe3O4, as well as the high thermal stability and film‐forming properties of PAN and PVP. Subsequently, carbonized PAN‐PVP/ Fe3O4 composite films with different Fe3O4 contents were successfully prepared by carbonization under high temperature inert atmosphere to convert PAN and PVP into carbon materials. It was found that the PAN‐PVP/ Fe3O4 porous carbon film with 3 wt% Fe3O4 addition had a conductivity of 3.99 S·mm−1 at a thickness of 0.42 mm, and an average EMI SET of 78.9 dB, SEA of 64.8 dB, and SSEt of 1838 dB/(cm2·g−1) in the X‐band, which is a typical wave absorbing material and can meet commercial electromagnetic shielding requirements. This work provides new ideas and methods for the research and development of polymer‐based porous carbonized film as electromagnetic shielding materials.Highlights The carbon films with rich porous structure were prepared. Fe3O4 was successfully embedded into the carbon film. Carbon films have an efficient conducting network. Carbon film has excellent electromagnetic shielding performance. The main shielding mode of carbon film is absorption.

Attitude motion and nonlinear free-surface deformation of stone-skipping over shallow water

Stone-skipping is a common yet complex motion that involves rigid-body dynamics and fluid–structure interaction (FSI). While many computational fluid dynamics methods are used to simulate the interaction between a stone and fluid, little research has been done to consider the stone, fluid, and fluid boundary as a whole in a simulation. This study, focuses on the attitude motion and free-surface deformation of stone-skipping over shallow water to investigate how the boundary effect of FSI impacts ricochet behaviors. Initially, we establish an iteration framework for the stone-skipping FSI issue based on a weakly compressible smoothed particle hydrodynamics (SPH) method with a Riemann solver. We conduct particle-independence verification and simulate several cases under varying water heights. Additionally, we analyze and compare ricochets in deep and shallow cases with different incident angles and initial pitch angles. The numerical results demonstrate that in shallow flow scenarios, the “comma-shaped” high-pressure area is compressed by the stone and the fluid boundary, leading to a more moderate variation in pitch angle. Stone-skipping in shallow water typically covers a shorter distance and reaches a lower height compared to deep water cases. Changes in the incident angle show that shallow water hinders successful skipping. Futhermore, different initial pitch angles reveal that water height directly impact the stone's trajectory in both horizontal and vertical directions. These highlight the connection between motion patterns and parameters, offering a reliable numerical prediction for the stone-skipping problem using the Riemann SPH method.

Numerical simulation study of hydrogen/air flame propagation and detonation characteristics in an annular cross section of gas turbine combustion chamber

The trends and future directions of hydrogen safety research cannot be separated from the thermodynamic behavior of combustion and explosion, hydrogen spontaneous combustion, flame propagation behavior, thermodynamic mechanisms, and other related topics. In this paper, through the method of numerical simulation, considering the hydrogen flame propagation and detonation characteristics in the annular section of the combustion chamber commonly used in gas turbines, the form of detonation and detonation impact in the channel are evaluated. By discussing the deflagration to detonation transition of hydrogen/air premixed gas and premixed gas under different working conditions, it is found that the flame in the annular channel propagates close to the inner wall and forms a strong expansion and turbulence between the outer wall and the outer wall of the flame. The flame surface and the airflow shear accelerate the detonation of hydrogen. The area close to the wall on the outer side of the flame surface and the tip of the flame surface are prone to set off detonation. The high-pressure area after the detonation mainly acts on the symmetrical end face of the outer wall surface and ignition area. There is a critical working temperature to make the impact strength strongest when the detonation occurs. Reducing the equivalence ratio of the filling gas can significantly reduce the reaction speed and weaken the impact strength of the wall. When the equivalence ratio is less than a certain value, the filling gas is completely consumed in the form of deflagration.

A pressure-jump EPR system to monitor millisecond conformational exchange rates of spin-labeled proteins.

Site-directed spin labeling electron paramagnetic resonance (SDSL-EPR) using nitroxide spin labels is a well-established technology for mapping site-specific secondary and tertiary structure and for monitoring conformational changes in proteins of any degree of complexity, including membrane proteins, with high sensitivity. SDSL-EPR also provides information on protein dynamics in the timescale of ps-μs using continuous wave lineshape analysis and spin lattice relaxation time methods. However, the functionally important time domain of μs-ms, corresponding to large-scale protein motions, is inaccessible to those methods. To extend SDSL-EPR to the longer time domain, the perturbation method of pressure-jump relaxation is implemented. Here, we describe a complete high-pressure EPR system at Q-band for both static pressure and ms-timescale pressure-jump measurements on spin-labeled proteins. The instrument enables pressure jumps both up and down from any holding pressure, ranging from atmospheric pressure to the maximum pressure capacity of the system components (~3500 bar). To demonstrate the utility of the system, we characterize a local folding-unfolding equilibrium of T4 lysozyme. The results illustrate the ability of the system to measure thermodynamic and kinetic parameters of protein conformational exchange on the ms timescale.

HYDROSTATIC TESTING TECHNOLOGIES IN THE METALLURGICAL INDUSTRY

The development of the new test presses is based on the requirements of modern technologies for the extraction of oil from ultra-deep wells and shale gas to test the strength of pipes up to higher test pressures. The hydrostatic test algorithm involves pushing test heads onto the ends of the pipe to seal the internal cavity of the pipe. Then the pipe is filled with a water emulsion and the pressure of this emulsion is increased to the value specified in regulatory documents. For high-pressure hydrostatic testing of oil and gas pipes, the most advantageous method is the external sealing of pipes using segmental sleeves. The mechanical testing equipment should take into account the compensation of axial forces from the pressure of the test fluid inside the pipe, for which purpose the press frame should be power-operated. The most common power scheme of test presses is considered, in which all axial forces arising from the action of the fluid pressure inside the pipe on the test heads are compensated by reaction forces in the power columns. The front head is rigidly connected to the columns, and the rear head is placed on a movable carriage to compensate for uneven pipe lengths. In the working position, the rear carriage is fixed to the columns with special locking mechanisms. It is advisable to improve the quality of the test by improving the design of the hydraulic system elements and studying the processes during the rise and retention of high pressure. The test pressure inside the pipe is created mainly by means of a hydraulic pressure multiplier. The parameters of the multiplier: multiplication factor, piston diameter and stroke are selected depending on the required test pressure, length and diameters of the pipes to be tested. Research on high-pressure hydraulic systems of the multiplier type is of particular interest at present.

Research on the pressure fluctuations and hydraulic resonance phenomena in the high-pressure pipelines of marine common rail systems

Increasing injection pressures in marine high-pressure common rail systems can lead to reliability issues due to pressure fluctuations. This study investigates the mechanism of hydraulic resonance caused by these fluctuations. A test bench assessed pressure fluctuations under various conditions and fuel pipe parameters, where hydraulic resonance was observed. Time-domain and frequency-domain analyses were conducted on the test results. The system pipeline was then optimized to eliminate hydraulic resonance. Resultsindicate that pressure fluctuations exhibit both high- and low-frequency coupling. Abnormal fluctuations are caused by hydraulic resonance, triggered by the proximity between the excitation frequency of the high-pressure fuel pump and the first-order natural frequency of the system. Resonance speed is influenced by the fuel pipe's structural parameters and the fuel's hydraulic properties. The frequency-domain model shows high predictive accuracy, identifying the interface between the pump and the pipeline as the most probable failure location. Optimization reduced pressure fluctuations at the pump end and the common rail by 73 % and 35.7 %, respectively, and eliminated hydraulic resonance at the original resonance speed. The maximum pressure fluctuation amplitude at the pump end decreased from 410 bar to 167 bar, a 59.3 % reduction. The research methodology presented in this paper provides a theoretical foundation for the structural design of the high-pressure pipeline in high-pressure common rail systems.

Canadian record-breaking wildfires in 2023 and their impact on US air quality

In recent years, extreme climate has increasingly triggered record boreal wildfires. The year 2023 saw a significant surge in wildfire occurrences in Canada, far surpassing the historical record. In this study, multi-source data were utilized for a comprehensive analysis of the development of the Canadian wildfires in 2023, the pathways of wildfire smoke, and its impact on the air quality in the US. The results indicate that the 2023 Canadian wildfires mainly occurred in western Canada (accounting for 60% of the burned area) and Quebec (eastern Canada, 29% of the burned area). Weather systems played a key role throughout wildfires and smoke plume transport processes. Specifically, high temperatures and dry weather caused by the blocking high-pressure systems was conducive to the enhancement of wildfire activities. Additionally, the southward airflow ahead of the ridge facilitated the transport of wildfires plume towards the south. This transport pattern frequently manifests under the Weather Regimes (WR) associated with the Alaskan Ridge (AkR) and Arctic High (ArH). In May and July, the smoke originating from the wildfires in western Canada, guided by the North American trough, affected the midwestern US. In June, smoke from eastern Canada led to severe air pollution in the northeastern US. Throughout the wildfire season, particulate matter dominated pollution in the US. The daily average PM2.5 concentration peaked at 258.9 μg/m³, exceeding the World Health Organization standard guidelines (15 μg/m³) by 17.3 times. This study highlights that wildfire has become one of the major environmental challenges facing the world under the influence of extreme climate.

Exploring the potential of supercritical carbon dioxide for eugenol impregnation in 3D printed polylactic acid structures

Biocompatible implants are essential for improving human health and longevity. Incorporating bioactive compounds, such as eugenol, into implant materials can improve biocompatibility and therapeutic efficacy. This study examines the effects of supercritical eugenol impregnation on the physical properties of 3D-printed polylactic acid samples produced by Fused Deposition Modeling. Impregnation was performed using a lab-scale high-pressure system, evaluating the impact of impregnation time on eugenol loading, distribution, and morphology. Fourier Transform Infrared spectroscopy confirmed homogeneous eugenol distribution with impregnation times exceeding 1 h, achieving loadings up to 12 wt%. Eugenol was released slowly over extended periods in a phosphate-buffered solution. Impregnated samples displayed more amorphous thermal behavior, with decreased Tg due to the plasticizing effect of the CO₂-eugenol mixture. Mechanical properties were slightly altered, with reduced stiffness and increased toughness. Microscopic deformations induced by impregnation could potentially enhance cellular adhesion, improving biocompatible material performance.

Reliability Analysis of High-Pressure Tunnel System Under Multiple Failure Modes Based on Improved Sparrow Search Algorithm–Kriging–Monte Carlo Simulation Method

It is often difficult for a structural safety design method based on deterministic analysis to fully and reasonably reflect the randomness of mechanical parameters, while the traditional reliability analysis method has a large calculation cost and low accuracy. In this paper, based on the seepage–stress coupling numerical model, the random variables affecting the reliability of the collaborative bearing of surrounding rock and lining structures are successfully identified. Then, the improved sparrow search algorithm (ISSA) is used to optimize the hyper-parameters of the Kriging surrogate model, in order to improve the computational efficiency and accuracy of the reliability analysis model. Finally, the ISSA-Kriging-MCS model is used to quantitatively evaluate the reliability of the surrounding rock-reinforced concrete lining structure under multiple failure modes, and the sensitivity of each random variable is discussed in depth. The results show that the high-pressure tunnel structure has high safety and reliability. The reliability indexes of each failure mode decrease with the increase in the coefficient of variation (COV) of random variables. In addition, the same random variable also exhibits varying degrees of influence in different failure modes.

Unveiling the devastating effect of the spring 2022 mega-heatwave on the South Asian snowpack

Global warming has led to a notable increase in heatwaves globally and regionally. In spring 2022, South Asia witnessed an unprecedented heatwave with temperatures breaking historical records and exceeding 5° C from climatological mean at several locations in the northern Indian subcontinent. Here, using 3D tracking, this heatwave ranked the most severe in the past 64 years, characterized by its protracted duration and wide spatial extent. The excess atmospheric heat, represented by temperature anomalies, during the mega-heatwave triggered rapid snowmelt across the snow-covered areas in the region, leading to an average loss of 42% in snow cover and 57% in snow depth of the regional snowpack. This rapid melting resulted in the complete disappearance of low-level snowpack in the western Himalayas, Pir Panjal, and Afghanistan highlands, leading to the lowest snowpack observed in the last six decades. Moreover, during the heatwave, the amount of snowfall received was only 29% of the long-term average. This combination of excessive melting and reduced snowfall culminated in a severe regional snow drought in spring 2022. The heatwave genesis lay a persistent high-pressure system over Northwest South Asia, reinforced by a quasi-stationary Rossby wave packet over Europe during the initial spell. Continuous heat from high-pressure ridges associated with circumglobal Rossby waves combined with the physical barrier of the Himalayas, lent staying power to this system during the second phase.

Experimental investigations of the impact of third-generation biodiesel and its blends on diesel fuel filter

Purpose Biodiesel in engines can reduce net carbon dioxide emissions and boost renewable energy. Despite the benefits of biodiesel engines, little is known about their effects on fuel filters. Filterability hinders the broad use of sustainable biodiesel, as filter clogging and deterioration can lead to engine damage and further hinder the widespread adoption of biodiesel. This study aims to investigate algae biodiesel (Chlorophyta) and diesel fuel filtration and filter deterioration to fill this gap. Design/methodology/approach This study investigates the effects of different biodiesel blends on diesel fuel filter parameters, namely, filter blocking tendency (FBT), tensile strength of filter medium upon immersion and other physiochemical properties. In total, 20% biodiesel and 80% diesel (B20) was chosen for its common use as a commercial blend, 40% biodiesel and 60% diesel (B40) for mid-level biodiesel content and 100% biodiesel (B100) for pure biodiesel testing. Testing these concentrations allowed us to determine the effect of increasing biodiesel content. B20 biodiesel emerges as the most suitable blend, providing the best balance of performance and durability with a low FBT (1.0) and a 6.9% increase in tensile strength over diesel. B40 and B100 had higher FBTs of 1.53 and 7.57, respectively, and lower tensile strength, resulting in increased filter clogging and material deterioration. SEM results demonstrated that B20-immersed filters had little structural changes as compared to B40 and B100; the colour darkened noticeably suggesting deposits, including sterol glucosides, indicating material deterioration and clogging. Findings The results from current study concluded that when compared to B40 and B100, the B20 biodiesel blend provides the best balance of performance and longevity, with less filter blockage, improved tensile strength and lower maintenance requirements. However, its performance in harsh settings, such as colder climes, high-pressure systems and engines requiring more power output, may require augmentation and more study. While higher blends may be more appropriate in some applications, B20 remains the most adaptable solution for a wide range of general operational situations. Originality/value The study concludes that the B20 biodiesel blend provides optimal performance, longevity and maintenance for compression ignition engines, exceeding other blends. While B40 and B100 may be appropriate in certain situations, B20 remains the most practical and versatile option, combining environmental benefits with engine compatibility, making it a superior alternative to standard diesel fuel.

A Physics Informed Neural Network for Solving the Inverse Heat Transfer Problem in Gas Turbine Rotating Cavities

Abstract Recently, Physics-Informed Neural Networks have displayed great potential in delivering swift and accurate solutions for inverse problems. Here, a Physics-Informed Neural Network (PINN) was used to solve the inverse heat conduction problem in the rotating cavities of a aeroengine high-pressure compressor internal air system. The neural network was designed to receive experimentally captured radially distributed temperature profiles as inputs and predict the associated surface heat fluxes. The correctness of these predicted heat fluxes are assessed by numerically solving the direct heat conduction equation using a 2D Finite-Element model, thereby recovering the original temperature profiles. A comparative analysis is conducted between the predicted temperature profiles and the initial inputs. The physics informed neural network is trained using noise free synthetic data, created from a range of radial temperature curve fit coefficients, and subsequently tested on noisy experimental data at engine representative conditions. The predicted temperature values exhibit some good agreement with their respective actual counterparts. Furthermore, the sensitivity of model hyperparameters are explored to showcase the capability of the proposed approach. The results show that Physics- Informed Neural Networks exhibit reduced susceptibility to experimental uncertainties when addressing inverse problems, in contrast to inverse solution methods, and offer a possible new approach for analysis of experimental data if trained on a sufficiently large dataset.

Nondispersive ultraviolet monitoring of pulsed H2S gas delivery

This article describes time-resolved optical measurements of H2S partial pressure and mass flow in a pulsed gas delivery system approximating injection conditions encountered during atomic layer deposition. A high-speed nondispersive ultraviolet (NDUV) gas analyzer design is employed for in-line H2S detection in a gas delivery line with flowing carrier gas. An in-place analyzer calibration performed in a reference cell yields an H2S detection limit of ≈1.4 Pa (at 22 °C) at a sampling rate of 1 kHz. Flow measurements performed on the delivery line are used to evaluate the effects of adjustable delivery parameters on the time-dependent injection system output. Short pulse widths exhibit partial pressure transients attributed to flow development within the different volumes of the delivery system. After ≈1.0 s of injection, steady-state flow is established across flow elements. A partial pressure of H2S in the delivery line is found to vary linearly with upstream H2S pressure, consistent with choked flow. A stronger scaling of partial pressure is evident when the flow coefficient of the downstream metering valve is adjusted. Estimated steady-state H2S flow rates in the range of 0.05–0.21 mg/s are observed within a limited range of valve flow coefficients. However, further increases in the flow coefficient do not result in increased flow, likely due to conductance limitations in downstream flow system components. The utility of NDUV absorption measurements for high-pressure pulsed gas delivery systems is discussed.

The cause of an extreme sea surface warming in the midlatitude western North Pacific during 2012 summer

This study investigated an extreme sea surface warming in the midlatitude western North Pacific (MLWNP) during the summer of 2012. The 2012 extreme event was characterized by warm sea surface temperature anomaly (SSTA) extending from the East/Japan Sea to central North Pacific. The SSTA box–averaged over the MLWNP (130–180°E, 33–50°N) in 2012 ranked as the third warmest in recent four decades, which has caused intense marine heatwaves in this region. During the summer of 2012, a positive Indian Ocean Dipole event co-occurred with El Niño, favoring anomalous moisture transport between the two basins that caused enhanced convection in the South China and Philippine Seas and western–to–central subtropical Pacific. The enhanced convective activities triggered two meridional atmospheric Rossby wave trains to form strong atmospheric blocking high–pressure systems in the MLWNP. This reduced the total cloud cover and surface wind speed, enhancing insolation and reducing the release of latent heat flux. In addition, the weakened wind strengthened the stratification and shoaled the mixed layer. As a result, the increased net heat flux into the ocean accompanied by a shallower mixed layer contributed to the upper ocean warming in the MLWNP. Meanwhile, the North Pacific was dominated by a negative phase of Pacific Decadal Oscillation (PDO), significantly contributing to warm SSTAs in the MLWNP in 2012. Consequently, the 2012 extreme warming in the MLWNP was the results of the combination of atmospheric Rossby waves and PDO. Our study highlighted the roles of high–frequency atmospheric teleconnection and low–frequency PDO in extreme sea surface warming in the MLWNP.

Revealing the mechanism of MgO inhibiting the combustion of modified double-base propellants

The regulation of burning rate is a key but challenging technology in the design of modified double-base propellants (MDBPs). In this study, the effect of magnesium oxide (MgO) on the combustion of MDBPs was investigated by using a high-pressure combustion experimental system at 1.0 MPa and different initial temperatures (−20, −10, 10, and 20 °C). MgO can reduce the burning rate, cause changes in the flame structure, and increase the burning surface thickness of MDBPs. To clarify the reasons for these phenomena, based on the density functional theory (DFT), the effects of MgO on the electrostatic interactions of nitroglycerin (NG) and nitrocellulose (NC) that are the key components in MDBPs and the reaction mechanisms between their decomposition products such as CH2O and NO2 on the MgO (100) surface were studied from a microscopic perspective. MgO not only decreases the nucleophilicity of NG and NC surfaces, but also reduces the reactivity of nitro and carbon chain regions, which leads to the difficulty in breaking the bond between the nitro and carbon chain regions, thus affecting its decomposition. In comparison to gas-phase reactions, the dehydrogenation barrier between CH2O and NO2 on the MgO (100) surface is higher. Thus, MgO inhibits the reaction between the decomposition products of NG and NC in the gas phase region. Therefore, MgO reduces the burning rate of MDBPs.

Electrical properties and redox stability of series novel high-entropy Bi2VO5.5-based oxides

Exceptional high ionic conductivities have been well documented in the Bi2VO5.5-based materials. However, the poor phase and redox stabilities under a reducing atmosphere hindered their wide applications. Herein, with the aim to improve the phase and redox stabilities under a reducing atmosphere, a high-entropy strategy of multiple-metal-doping was applied to prepare series Bi2V1–4x(GaSiTaZr)xO5.5-δ (0 ≤ x ≤ 0.1) materials by a traditional solid state reaction method. The results revealed that multiple-metal-doping could stabilize the tetragonal phase of Bi2VO5.5 to room temperature and shown good phase and structural stabilities under inert or high oxygen partial pressure atmospheres, as well as pure oxide ion conduction which was about two orders of magnitude higher than that of the parent material, e.g. ∼2.0×10−2 S/cm at 400 ºC for the x = 0.05 sample while ∼1.5×10−4 S/cm for the x = 0 sample. Although the Bi2V1–4x(CuNiNbTi)xO5.5-δ materials would still be readily reduced under a reducing environment and introduce strong electronic conduction, the phase stability was apparently improved. Thus, improving the redox stability and suppressing the electronic conduction of the stabilized Bi2VO5.5-based materials under a reducing atmosphere is still the direction we should strive for.

Compound spatial extremes of heatwaves and downstream air pollution events in East Asia

In light of increasing climate hazards globally that pose risk to public health, the compounded effects of two major hazards, heatwaves and air pollution, have become a focal point for environmental and health research. This study explores the intricate relationship between extreme temperature events in North China (NC) and South China (SC) – two prominent areas of aerosol exposure in East Asia – and the associated changes in aerosol optical depth (AOD) across the region. The heatwave events and regional AOD distribution revealed distinct patterns in their respective regions from June to September. Both NC and SC showed reduced AOD during heatwave events, while downstream regions experienced increased AOD levels. From the perspective of heatwaves in NC and SC, we present a more holistic picture of how large-scale modulators contribute to inducing air pollution hazards across East Asia. The analysis revealed a link between blocking high-pressure system and heatwave occurrences in NC, while a dominant Rossby wave train, influenced by the South China Sea, was identified as a major modulator in SC. Additionally, other large-scale circulatory systems, such as the Western Pacific Subtropical High, the East Asian jet stream, and the South Asian High, also play crucial roles in shaping these events. This suggests the potential for predicting downstream AOD events. The study underscores the importance of understanding the interconnectedness of meteorological and air quality phenomena to mitigate the adverse environmental impacts in East Asia.

Simulation and Mechanistic Exploration of the Mid to Late-Stage Hydrothermal Carbonization Process in Biomass

Using C143H108O4 as the model for hydrochar, unsaturated small molecules necessary for polymerization reactions were added to extend the simulation of the hydrothermal carbonization (HTC) growth process. This enabled a comprehensive exploration of the pressure (density), small-molecule structure, water influence conditions, and related HTC reaction mechanisms in the middle to late stages of the process. The simulation results indicate that in a high-pressure system with a simulated pressure of 200MPa, there is a greater quantity of hydrochar formation when compared to systems at lower pressures. The addition of unsaturated small molecules, such as CH2O2, C4H5O, C4H6, C3H4, and C4H5 reduces the need for intermolecular dehydrogenation or hydrogen transfer reactions in the system, indirectly accelerating subsequent HTC reactions. In particular, the addition of H2O was detrimental to mid to late-stage HTC reactions, which are primarily dominated by both polymerization and aromatization reactions, as the addition was found to significantly increase the level of free H in the system. Consequently, compared with the absence of water, this results in the formation of a relatively hydrogen-rich environment in the molecular system, contrary to the requirements of mid to late-stage HTC reactions. Additionally, a recurring observation in mid to late-stage HTC reactions is the continuous occurrence and repetition of “polymerization-decomposition-polymerization” processes among large fragment molecules, representing a transition from unstable to relatively stable structures. Aromatization between fragments is crucial for transition to stable structures. Finally, in conjunction with wavefunction analysis of the polymer, it was observed that the aromatic polymer interactions gradually exerted a significant influence on the molecular structure as the temperature decreased to room temperature at 300K. This resulted in the gradual clustering of molecular structures, potentially contributing to the spherical and core-shell structures of the hydrochar microparticles.

Impact of the Changbai Mountains’ topography on spring fog over the Bohai Sea

Fog is a highly complex weather phenomenon influenced by numerous factors. This study investigated the impact of the Changbai Mountains’ topography on the formation and development of spring fog in the Bohai Sea. From 12 to 14 May 2021, the Bohai region experienced a sea fog event. Utilizing Himawari-8 satellite data, ERA5 reanalysis dataset, land and sea station observations, the WRF model, a topography sensitivity experiment, and backward trajectory tracking, the influence of the Changbai Mountains’ topography on the evolution of this sea fog event was assessed. Results indicated that the Changbai Mountains’ topography significantly impacted the propagation and concentration of the sea fog through dual effects—namely, the Venturi Effect and Foehn Clearance Effect. Comparative simulations incorporating and excluding the Changbai Mountains revealed that its topography favored weak convergence (Venturi Effect) of low-level airflow over the Bohai Sea induced by a high-pressure system, promoting westward fog expansion. Additionally, the backward trajectory analysis further indicated that the Foehn Clearance Effect of the Changbai Mountains extended its influence far beyond the immediate lee side, contributing to significant changes in atmospheric conditions such as reductions in relative humidity and increases in potential temperature. The dry, warm foehn contributed to a reduction in the liquid water content, ultimately leading to the weakening or even dissipation of the sea fog in the region close to the Changbai Mountains. This study emphasizes the crucial role of the Changbai Mountains’ topography in the development and evolution of fog, providing valuable insights for forecasting fog in regions with complex terrain.