Residence Time Analysis Research Articles

Solvation Structures and Transport Mechanisms of Cations in Water-in-Bisalt Electrolytes for High-Concentration Lithium-Ion Batteries Revealed by Molecular Dynamics Simulations.

The development of safe and cost-effective electrolytes for rechargeable batteries is currently underway. While water-based electrolytes hold promise, their restricted electrochemical stability window poses a challenge. Combining multiple ionic species emerges as a promising strategy to broaden this stability window and optimize Li-ion battery performance. This study focuses on dual-cation electrolytes, which blend lithium and potassium acetates to enhance the electrochemical characteristics of the solution at high concentrations. We investigated the solvation structure of each ion and its interactions on a molecular level. Our analysis reveals that ion clusters and aggregates are formed through shared acetate and water molecules at high salt concentrations. Furthermore, the residence time analyses of atom pairs indicate that cations diffuse in vehicular mode at low concentrations. In contrast, they switch to a structural mode at high concentrations due to diminishing water content. This study offers a comprehensive model for exploring diverse solvation structures of cations and gaining insights into their diffusion mechanisms within water-in-bisalt electrolytes for aqueous Li-ion batteries.

Numerical analysis of residence time for particle impregnation in a rotating drum

The impregnation is a key step for handling particles in various chemical engineering processes, which requires uniform distribution of active ingredients over particles. This paper describes the effects of particle residence time in the impregnation area on the inter-particle impregnation variability in a rotating drum. The discrete element method is used to simulate the particle dynamics and the image analysis method is used to model the spray impregnation process. It is observed that the coefficient of inter-particle impregnation variability decreases over time and converges to an asymptotic value, which depends on the particle size and the width of the impregnation area. The dead zone of impregnation near the inclined side walls of the drum is identified, which can be reduced by widening the impregnation area. In addition, the relative standard deviation of residence time for particles in the impregnation area also decrease with the increase of particle size and impregnation area width. With various particle sizes and impregnation areas, it is found that the inter-particle impregnation variability is linearly related to the relative standard deviation of the residence time of the particles in the impregnation area, since the exposure of particles in the spray area controls the impregnation over particles. This study provides fundamental insights for optimizing the particle impregnation process in a rotating drum.

Ultrasonic and conversion-based inline fouling measurements for continuous emulsion copolymerisation of vinyl acetate in a tubular reactor.

One of the serious challenges for the implementation of continuous emulsion polymerisation is their significant fouling. The elucidation of time-dependent fouling processes and the development of inline analysis methods for fouling mass quantification are crucial to making progress in this area. Inline-sensor concepts based on ultrasonic measurements as well as residence time and conversion analysis were investigated regarding their suitability for the detection of time-dependent fouling formation and compared with gravimetrical results in order to validate their precision. Both a set-up using a turnover analysis for determination of losses in reaction volume by fouling and an ultrasound-based measurement system detecting deposit-caused changes by evaluating the average sound velocity could be used as suitable sensor concepts. The accuracies of both sensors are below 10% deviation to fouling references.

Land reclamation and its consequences: A 40-year analysis of water residence time in Doha Bay, Qatar.

Qatar's rapid industrialization, notably in its capital city Doha, has spurred a surge in land reclamation projects, leading to a constriction of the entrance to Doha Bay. By reducing and deflecting the ocean circulation, land reclamation projects have reduced the effective dispersion of wastewater introduced into the bay and hence degraded the water quality. Here, we assess fluctuations in water residence time across three distinct eras (1980, 2000, and 2020) to gauge the impact of successive land reclamation developments. To do this, we couple the multi-scale ocean model SLIM with a Lagrangian model for water residence time within Doha's coastal area. We consider three different topographies of Doha's shoreline to identify which artificial structures contributed the most to increase water residence time. Our findings reveal that the residual ocean circulation in Doha Bay was predominantly impacted by northern developments post-2000. Between 1980 and 2000, the bay's residence time saw a modest rise, of about one day on average. However, this was followed by a substantial surge, of three to six days on average, between 2000 and 2020, which is mostly attributable to The Pearl mega artificial island development. Certain regions of the bay witnessed a tripling of water residence time. Given the ongoing population expansion along the coast, it is anticipated that the growth of artificial structures and coastal reclamation will persist, thereby exacerbating the accumulation of pollutants in the bay. Our findings suggest that artificial offshore structures can exert far-reaching, non-local impacts on water quality, which need to be properly assessed during the planning stages of such developments.

Impact analysis of hydraulic residence time and dissolved oxygen on performance efficiency and microbial community in N, N-dimethylformamide wastewater treated by an AnSBR-ASBR

Suitable operating parameters are one of the key factors to efficient and stable biological wastewater treatment of N, N-dimethylformamide (DMF) wastewater. In this study, an improved AnSBR-ASBR reactor (anaerobic sequencing batch reactor, AnSBR, and aerobic SBR, ASBR, run in series) was used to investigated the effects of operating conditions such as hydraulic residence time (HRT), AnSBR stirring speed and ASBR dissolved oxygen (DO) for DMF wastewater treatment. When HRT decreased from 24 h to 12 h, the average removal rates of COD by the AnSBR were 34.59% and 39.54%, respectively. Meanwhile, the removal rate of NH4+-N by ASBR decreased from 88.38% to 62.81%. The DMF removal rate reached the best at 18 h and the expression of dehydrogenase was the highest in the AnSBR. The abundance of Megasphaera, the dominant sugar-degrading bacteria in the AnSBR, continued to decline due to the decrease of HRT. The relative abundance of Methanobacterium gradually increased to 80.2% with the decrease of HRT and that hydrotrophic methanogenesis dominated the methanogenic process. The HRT decrease promoted butyrate and pyruvate metabolism in anaerobic sludge, but the proportion of glycolysis and methane metabolism decreased. The AnSBR-ASBR reactor had the best operation performance when HRT was 18 h, AnSBR speed was 220 r/min, and ASBR DO content was 3–4 mg/L. This study provided an effective reference for the reasonable selection of operating parameters in the treatment of DMF-containing wastewater by the AnSBR-ASBR.

Purpurogallin ameliorates sevoflurane-induced cognitive impairment and hippocampal neuroinflammation in neonatal mice

Postoperative cognitive dysfunction contributes to memory impairment, which is involved in neurotoxicity, endoplasmic reticulum stress, calcium overload and hippocampal neuron apoptosis. Purpurogallin can mitigate ischemia-induced neuronal injury and microglial inflammation. However, whether purpurogallin affects cognitive dysfunction remains unclear. To investigate the efficacy of purpurogallin on cognitive dysfunction and explore the potential signal pathways, Sevoflurane (SEV)-induced model was established on mice, and water maze testing was performed to record escape latency, platform residence time, platform crossings and swimming speed analysis. The concentration of Interleukin (IL)-6, IL-1β and Tumor necrosis factor (TNF)-α in hippocampus tissue were evaluated using Enzyme-linked immunosorbent assay (ELISA). The hippocampal neurons were analyzed using Nissl staining. The Iba-1 was evaluated using immunofluorescent assay (IFA), while the cell apoptosis was assessed using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Western blots were performed to evaluate the expression of Ionized calcium binding adaptor molecule 1 (Iba1), integrin α-M (CD11b), Bax, integrin α-M (Bcl-2), p-65 and IκBα, as well as the phosphorylation of p-65 and IκBα. Purpurogallin at dose of 150 mg/kg significantly reduced escape latency in SEV-induced mice (p < 0.001), without affecting swimming speed. It increased time spent in the target quadrant and restored platform crossings reduced by SEV. Purpurogallin also mitigated the elevated IL-6, IL-1β and Transforming growth factor alpha (TGF-α) levels caused by SEV in the hippocampus, preserved Nissl bodies, and reduced Iba-I and CD11b expression (p < 0.01). It alleviated cell apoptosis by downregulating Bax and upregulating Bcl-2, while inhibiting p-65 phosphorylation and promoting IκBα phosphorylation induced by SEV (p < 0.05). Purpurogallin effectively countered SEV-induced cognitive impairment, neuroinflammation, hippocampal injury, microglial activation and neuronal apoptosis through inhibiting nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, which facilitate purpurogallin to become a drug candidate for postoperative cognitive dysfunction.

Source characterization of volatile organic compounds at Carlsbad Caverns National Park

ABSTRACT Carlsbad Caverns National Park (CAVE), located in southeastern New Mexico, experiences elevated ground-level ozone (O3) exceeding the National Ambient Air Quality Standard (NAAQS) of 70 ppbv. It is situated adjacent to the Permian Basin, one of the largest oil and gas (O&G) producing regions in the US. In 2019, the Carlsbad Caverns Air Quality Study (CarCavAQS) was conducted to examine impacts of different sources on ozone precursors, including nitrogen oxides (NOx) and volatile organic compounds (VOCs). Here, we use positive matrix factorization (PMF) analysis of speciated VOCs to characterize VOC sources at CAVE during the study. Seven factors were identified. Three factors composed largely of alkanes and aromatics with different lifetimes were attributed to O&G development and production activities. VOCs in these factors were typical of those emitted by O&G operations. Associated residence time analyses (RTA) indicated their contributions increased in the park during periods of transport from the Permian Basin. These O&G factors were the largest contributor to VOC reactivity with hydroxyl radicals (62%). Two PMF factors were rich in photochemically generated secondary VOCs; one factor contained species with shorter atmospheric lifetimes and one with species with longer lifetimes. RTA of the secondary factors suggested impacts of O&G emissions from regions farther upwind, such as Eagle Ford Shale and Barnett Shale formations. The last two factors were attributed to alkenes likely emitted from vehicles or other combustion sources in the Permian Basin and regional background VOCs, respectively. Implications: Carlsbad Caverns National Park experiences ground-level ozone exceeding the National Ambient Air Quality Standard. Volatile organic compounds are critical precursors to ozone formation. Measurements in the Park identify oil and gas production and development activities as the major contributors to volatile organic compounds. Emissions from the adjacent Permian Basin contributed to increases in primary species that enhanced local ozone formation. Observations of photochemically generated compounds indicate that ozone was also transported from shale formations and basins farther upwind. Therefore, emission reductions of volatile organic compounds from oil and gas activities are important for mitigating elevated O3 in the region.

Effect of film thickness and temperature on condensation and momentum accommodation at the liquid–vapor methane interphase in contact with a quartz substrate

In this paper, we used the Molecular Dynamics method to simulate the equilibrium vapor–liquid methane in contact with a solid quartz substrate and study the condensation process and momentum exchange at the atomic level. A large potential cutoff radius is used to determine the vapor and liquid densities at good accuracy. By tracking the motions of fluid molecules exchanged between the vapor and liquid phases and carrying out statistical analysis of residence time, penetration depth and especially velocity correlation, the mass and the velocity accommodation coefficients can be determined at the same time. The latter is based on the assumption that the reflected events take place over a short time, near the interface and thus atoms velocities are correlated while the condensation/evaporation events are not. The calculated coefficients are sensitive to the film thickness due to the presence of the quartz substrate and the layering effects. As temperature increases, atoms condense less and reflect more and the reflection is more diffusive due to increasing collision rate. Near the critical temperature, both the condensation and momentum accommodation coefficients vary significantly.

Influence of atmospheric circulation and local parameters on activity concentration of gross alpha and gross beta in Granada, Spain

This work analyses the influence of local meteorology and air mass origin on radioactivity levels measured in Granada (Southern Spain). To the scope, gross α and gross β activities at ground-level air were weekly recorded from 2006 to 2021, by collecting aerosol filters and successively analysing them by low-level proportional counting. Time series decomposition shows a strong correlation between the seasonal components of gross α and gross β and the local meteorological parameters, in particular temperature and wind speed. Back trajectories reaching the study area during the sampling, calculated at three height levels (750 m, 1500 m, and 3000 m a.s.l.), were analysed by three methods with the aim to determine the main characteristics of air masses reaching Granada, and their impact on airborne radioactivity levels. The results of the residence time and clustering analyses showed that an increase in the radioactivity levels in the southeast of Spain is connected with air masses coming from the Mediterranean at 750 m and from the South (Sahara Desert) at 3000 m. In line with the outcomes obtained by the cluster analysis, the Concentration Weighted Trajectory (WCWT) results highlight that the air masses transported from Mediterranean and African regions are a potential source of gross α and gross β. Moreover, the findings of the WCWT bring a new aspect by revealing that the southern France region can also have a significant contribution to gross alpha and beta activities.

How to design a low-cost pilot scale magnetic bioseparation process for protein separation from complex mixtures using in-line process analytics

Magnetic separation is a powerful tool for the integrated capture and purification of biomolecules and cells directly from complex feed media without the need for prior clarification and without the risk of equipment blockage. In this study, we equipped a commercially available rotor–stator high-gradient magnetic separator (RS-HGMS) with in-line analytics of hygienic design (absorbance, conductivity, pH, and flow) and used it for a systematic characterization of the equipment. By combining particle agglomeration and separation studies with residence time analysis, magnetic filter capacity, and particle retention experiments for bare iron oxide nanoparticles (BIONs), we developed a generic RS-HGMS operation protocol optimized for minimal particle carry-over and efficient buffer exchange. To demonstrate the versatility of our approach, we customized this operation protocol for the challenging task of lactoferrin separation from crude acid whey, which serves as an illustrative example in this paper. The modifications involved simple adjustments of pump speed, step duration, and cycle repetition without altering the fundamental principles of our generic approach. In this proof-of-concept, a BIONs carry-over of less than 0.037 g L-1 was achieved in the elution fractions, and the in-line sensors enabled continuous monitoring and documentation of the process, providing valuable data for process optimization and validation. This paper demonstrates how a magnetic separation process can be effortlessly tailored for challenging bioseparation tasks, while emphasizing the importance of implementing continuous in-line process monitoring and data logging. We believe this is an essential step toward the wider adoption of this promising technique in the industry.

Development of AMOEBA Polarizable Force Field for Rare-Earth La3+ Interaction with Bioinspired Ligands.

Rare-earth metals (REMs) are crucial for many important industries, such as power generation and storage, in addition to cancer treatment and medical imaging. One promising new REM refinement approach involves mimicking the highly selective and efficient binding of REMs observed in relatively recently discovered proteins. However, realizing any such bioinspired approach requires an understanding of the biological recognition mechanisms. Here, we developed a new classical polarizable force field based on the AMOEBA framework for modeling a lanthanum ion (La3+) interacting with water, acetate, and acetamide, which have been found to coordinate the ion in proteins. The parameters were derived by comparing to high-level ab initio quantum mechanical (QM) calculations that include relativistic effects. The AMOEBA model, with advanced atomic multipoles and electronic polarization, is successful in capturing both the QM distance-dependent La3+-ligand interaction energies and experimental hydration free energy. A new scheme for pairwise polarization damping (POLPAIR) was developed to describe the polarization energy in La3+ interactions with both charged and neutral ligands. Simulations of La3+ in water showed water coordination numbers and ion-water distances consistent with previous experimental and theoretical findings. Water residence time analysis revealed both fast and slow kinetics in water exchange around the ion. This new model will allow investigation of fully solvated lanthanum ion-protein systems using GPU-accelerated dynamics simulations to gain insights on binding selectivity, which may be applied to the design of synthetic analogues.

PM2.5 in Carlsbad Caverns National Park: Composition, sources, and visibility impacts

ABSTRACT Carlsbad Caverns National Park in southeastern New Mexico is adjacent to the Permian Basin, one of the most productive oil and gas regions in the country. The 2019 Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, oil and gas development, wildfires, and soil dust on air quality in the park. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here, we focus on observations of fine particles and key trace gas precursors to understand the important contributing species and their sources and associated impacts on haze. Key gases measured included aerosol precursors, nitric acid and ammonia, and oil and gas tracer, methane. High-time resolution (6-min) PM2.5 mass ranged up to 31.8 µg m−3, with an average of 7.67 µg m−3. The main inorganic ion contributors were sulfate (avg 1.3 µg m−3), ammonium (0.30 µg m−3), calcium (Ca2+) (0.22 µg m−3), nitrate (0.16 µg m−3), and sodium (0.057 µg m−3). The WSOC concentration averaged 1.2 µg C m−3. Sharp spikes were observed in Ca2+, consistent with local dust generation and transport. Ion balance analysis and abundant nitric acid suggest PM2.5 nitrate often reflected reaction between nitric acid and sea salt, forming sodium nitrate, and between nitric acid and soil dust containing calcium carbonate, forming calcium nitrate. Sulfate and soil dust are the major contributors to modeled light extinction in the 24-hr average daily IMPROVE observations. Higher time resolution data revealed a maximum 1-hr extinction value of 90 Mm−1 (excluding coarse aerosol) and included periods of significant light extinction from BC as well as sulfate and soil dust. Residence time analysis indicated enrichment of sulfate, BC, and methane during periods of transport from the southeast, the direction of greatest abundance of oil and gas development. Implications: Rapid development of U.S. oil and gas resources raises concerns about potential impacts on air quality in National Parks. Measurements in Carlsbad Caverns National Park provide new insight into impacts of unconventional oil and gas development and other sources on visual air quality in the park. Major contributors to visibility impairment include sulfate, soil dust (often reacted with nitric acid), and black carbon. The worst periods of visibility and highest concentrations of many aerosol components were observed during transport from the southeast, a region of dense Permian Basin oil and gas development.

Development and application of a street-level meteorology and pollutant tracking system (S-TRACK)

Abstract. A multi-model simulation system for street-level circulation and pollutant tracking (S-TRACK) has been developed by integrating the Weather Research and Forecasting (WRF), the STAR-CCM+ (computational fluid dynamics model – CFD), and the Flexible Particle (FLEXPART) models. The winter wind environmental characteristics and the potential contribution of traffic sources to nearby receptor sites in a city district of China are analysed with the system for January 2019. It is found that complex building layouts change the structure of the wind field and thus have an impact on the transport of pollutants. The wind speed inside the building block is lower than the background wind speed due to the dragging effect of dense buildings. Ventilation is better when the dominant airflow is in the same direction as the building layout. Influenced by the building layout, the local circulations show that the windward side of the building is mostly the divergence zone, and the leeward side is mostly the convergence zone, which is more obvious for high buildings. With the hypothesis that the traffic sources are uniformly distributed on each road and with identical traffic intensity, the potential contribution ratios (PCRs) of four traffic sources to certain specific sites under the influence of the street-level circulations are estimated with the method of residence time analysis. It is found that the contribution ratio varies with the height of the receptor site. As a result of the generally upward motion in the airflow, the position with the greatest PCR from the four road traffic sources is located at a certain height which is commonly influenced by the distance of this location from the traffic source and the background wind field (about 15 m in this study). The potential contribution of a road to one of the receptor sites is also investigated under different wind directions. The established system and the results can be used to understand the characteristics of urban wind environment and to help the air pollution control planning in urban areas.

Characterization of electrohydrodynamic flow in a plate-plate electrostatic precipitator with a wire-cylinder pre-charger by data-driven vortex and residence time analysis

The two-stage electrostatic precipitator (ESP) is widely used for indoor air cleaning field, while both the Particle Image Velocimetry (PIV) observations and well-characterized quantitative descriptions are probably scarce. In this work, we propose to use vortex analysis, which is the main quantitative method for flow field, and the relative residence time method (RRT) to evaluate the electrohydrodynamic flow (EHD) in a plate-plate ESP. The effects of electrical energization, pre-charger polarity and primary gas flow velocity are studied. Two vortex indexes sort the particle flow as five patterns and increase almost linearly with applied voltage. Four final particle statuses, penetrated, collected, stagnant and back-mixed are clarified by RRT method. The data generated by RRT are utilized to derive the PIV index for further analysis of the ESP performance. The trend, which rises first and drops later, suggests PIV index is expected to pave a new way to clarify the relationship between the ESP flow patterns and particle collection efficiency.

Potential contribution of distant sources to airborne Betula pollen levels in Northeastern Iberian Peninsula

Betula (birch) pollen is one of the most important causes of respiratory allergy in Northern and Central Europe. While birch trees are abundant in Central, Northern, and Eastern Europe, they are scarce in the Mediterranean territories, especially in the Iberian Peninsula (IP), where they grow only in the northern regions and as ornamental trees in urban areas. However, the airborne birch pollen patterns in Catalonia (Northeastern IP) show abrupt high concentrations in areas with usually low local influence. The intensity of the derived health problems can be increased by outbreaks due to long-range pollen transport. The present work evaluates the different potential contributions to Catalonia from the main source regions: Pyrenees, Cantabria, and the forests of France and Central Europe. To this end, we computed the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) back trajectories of air masses associated with the main Betula pollen peaks occurring simultaneously over different Catalan monitoring stations, and we studied their provenance over a 15-year period. The Vielha aerobiological station on the northern slopes of the Central Pyrenees was used to identify the dates of the pollen season in the Pyrenean region. In order to better understand the role of the Pyrenees, which is the nearest of the four birch forested regions, we classified the pollen peaks in the other Catalan stations into three groups based on the relationship between the peak and the pollen season in the Pyrenees. Our analysis of back-trajectory residence time, combined with the associated pollen concentration, reveals that two principal routes other than the Pyrenean forest sustain the northerly fluxes that enter Catalonia and carry significant concentrations of Betula pollen. This study has also allowed quantifying the differentiated contributions of the potential source regions. In addition, the Weather Research Forecast (WRF) mesoscale model has been used to study three specific episodes. Both models, HYSPLIT and WRF, complement each other and have allowed for better understanding of the main mechanisms governing the entry of birch pollen to the region.

Impacts of secondary aerosol formation and long range transport on severe haze during the winter of 2017 in the Seoul metropolitan area

Severe haze episodes occur frequently in the Seoul Metropolitan Area (SMA) and throughout East Asian countries, especially during the winter and early spring. We investigated the sources and chemistry of particulate matter (PM) during three winter haze episodes in Seoul that occurred between January 1st and February 10th in 2017 using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and positive matrix factorization (PMF) analysis.The average concentration of sub-micrometer aerosol (PM1 = NR-PM1 + black carbon (BC)) was 32.6 μg/m3, which was composed of 42% organics, 27% nitrate, 11% sulfate, 13% ammonium and 4% BC by mass. Six distinct sources of organic aerosol (OA) were identified: vehicle emitted hydrocarbon-like OA (HOA), cooking OA (COA), biomass burning OA (BBOA), and 3 different types of secondary OA (SOA) with varying degrees of oxidation and temporal trends.The nitrate mass fraction increased during the three haze episodes, with nitrate accounting for 27-33% of PM1 mass. Enhanced nitrate concentrations and higher nitrate oxidation ratios (NOR), despite lower enhancement in relative humidity (RH) than the low PM loading period, suggest that regional transport of nitrate contributed to the nitrate mass during the haze periods.Lower HOA and COA concentrations during the high PM loading periods further confirm that local emissions or stagnant meteorological conditions were not the main reason for the severe haze. Residence time analysis (RTA), concentration field analysis (CFA), and column-CFA results from FLEXPART also showed that the measurement period was accompanied by atmospheric transport of nitrate, sulfate, and ammonium from eastern China. Nevertheless, we found that NO2, a precursor of nitrate, was predominantly from local emissions. These findings suggest that nitrate in Seoul is not only locally formed, but also transported from upwind areas.

On the processes governing the variability of PTR-MS based VOCs and OVOCs in different seasons of a year over hillocky mega city of India

The rapidly increasing industrialization and urbanization, in combination with under representation of in-situ measurements, especially Volatile Organic Compounds (VOCs), has posed serious challenges in understanding air quality and atmospheric chemistry over India. Here we present yearlong measurements of VOCs, carried out during March 2014–February 2015 using a Proton Transfer Reaction Mass Spectrometer (PTR-MS) from an urban site Pune (18.58oN, 73.91°E, 559 m amsl) in western tropical India. The averaged diurnal variation in VOCs at Pune exhibited a characteristic bimodal pattern, with highly pronounced peak during morning hours and secondary enhancement during late evening/night, except for Isoprene. Isoprene mixing ratios were observed to be higher (1.30 ± 0.69 ppbv) during the daytime (0900–1800 h) and lower (0.89 ± 0.65 ppbv) during the nighttime (after 1900 h and before 0900 h). While, Methanol, Acetonitrile, and Acetaldehyde are observed to be the highest (14.3 ± 5.9, 0.9 ± 0.4, and 6.1 ± 2.6 ppbv respectively) during spring, Benzene and Toluene were highest (1.6 ± 1.1, 2.6 ± 2.2 ppbv respectively) during winter. Isoprene mixing ratios showed broader maxima during autumn and winter (1.3 ppbv). Nominally, all the VOCs were observed to be lowest during the monsoon season. The two peaks in the seasonal cycle of acetonitrile along with VIIRS retrieved fire counts indicated impact of the regional biomass burning during spring and winter. Analysis of air-mass residence time further revealed potential influences from the highly polluted Indo-Gangetic Plain during the autumn and winter, whereas local pollution supplemented with regional biomass burning found to be the dominant process during spring. These yearlong measurements are a step forward in filling a major gap of observational data of VOCs over the tropical Indian region, which would be invaluable for evaluation of chemistry transport models and understanding of regional tropospheric chemistry.

Effect of temperature on concentrated electrolytes for advanced lithium ion batteries.

Salt-concentrated electrolytes are emerging as promising electrolytes for advanced lithium ion batteries (LIBs) that can offer high energy density and improved cycle life. To further improve these electrolytes, it is essential to understand their inherent behavior at various operating conditions of LIBs. Molecular dynamics (MD) simulations are extensively used to study various properties of electrolytes and explain the associated molecular-level phenomena. In this study, we use classical MD simulations to probe the properties of the concentrated electrolyte solution of 3 mol/kg lithium hexafluorophosphate (LiPF6) salt in the propylene carbonate solvent at various temperatures ranging from 298 to 378K. Our results reveal that the properties such as ionic diffusivity and molar conductivity of a concentrated electrolyte are more sensitive to temperature compared to that of dilute electrolytes. The residence time analysis shows that temperature affects the Li+ ion solvation shell dynamics significantly. The effect of temperature on the transport and dynamic properties needs to be accounted carefully while designing better thermal management systems for batteries made with concentrated electrolytes to garner the advantages of these electrolytes.

Fluid Flow Characteristics of Healthy and Calcified Aortic Valves Using Three-Dimensional Lagrangian Coherent Structures Analysis

Aortic valve calcification is an important cardiovascular disorder that deteriorates the accurate functioning of the valve leaflets. The increasing stiffness due to the calcification prevents the complete closure of the valve and therefore leads to significant hemodynamic alterations. Computational fluid dynamics (CFD) modeling enables the investigation of the entire flow domain by processing medical images from aortic valve patients. In this study, we computationally modeled and simulated a 3D aortic valve using patient-specific dimensions of the aortic root and aortic sinus. Leaflet stiffness is deteriorated in aortic valve disease due to calcification. In order to investigate the influence of leaflet calcification on flow dynamics, three different leaflet-stiffness values were considered for healthy, mildly calcified, and severely calcified leaflets. Time-dependent CFD results were used for applying the Lagrangian coherent structures (LCS) technique by performing finite-time Lyapunov exponent (FTLE) computations along with Lagrangian particle residence time (PRT) analysis to identify unique vortex structures at the front and backside of the leaflets. Obtained results indicated that the peak flow velocity at the valve orifice increased with the calcification rate. For the healthy aortic valve, a low-pressure field was observed at the leaflet tips. This low-pressure field gradually expanded through the entire aortic sinus as the calcification level increased. FTLE field plots of the healthy and calcified valves showed a variety of differences in terms of flow structures. When the number of fluid particles in the healthy valve model was taken as reference, 1.59 and 1.74 times more particles accumulated in the mildly and severely calcified valves, respectively, indicating that the calcified valves were not sufficiently opened to allow normal mass flow rates.

Long-term trends in particulate sulfate at Grand Canyon National Park

Visibility impairment, particularly at the iconic southwestern U.S. national parks, was an early and persistent concern that helped motivate parts of the Clean Air Act (CAA) and its 1977 and 1990 amendments. Grand Canyon National Park (GCNP), Arizona, in particular, was the site of many early air quality studies that found that before 1990 particulate sulfate was the largest contributor to light extinction at GCNP. Since a peak in the 1960s, sulfate concentrations at GCNP have declined dramatically as sulfur dioxide (SO2) emissions in the southwestern United States and northern Mexico have been reduced, often due to successful regulations. The relative importance of upwind source regions has also changed. During the 1960s and 1970s the predominant SO2 emitters were copper smelters in Arizona and surrounding states. As smelter emissions declined, in the 1980s and 1990s electric generating units (EGUs) became the largest upwind SO2 sources. More recently, EGU emissions have also been reduced, especially since about 2000. Three back trajectory methods are used to examine the sulfate concentrations at GCNP as a function of upwind source regions. 1) Residence time analysis shows that Arizona, southern California, southern Utah, and northern Mexico are most often upwind of GCNP. There were highly significant reductions in mean sulfate concentrations at GCNP when air arrived after transport through most source regions. 2) Concentration trends by source region show that the maximum rates of decline for 1980–2018 were about −2%/year when there was transport through Colorado and the Navajo Generating Station (NGS) source regions. 3) The Trajectory Mass Balance (TrMB) model was used to apportion sulfate seasonally for 3-year rolling averages during 1981–2017. As expected, relative source attributions have evolved through time. Largest mean contributors in summer are northern Mexico (25–70%), Baja (0–25%), Arizona smelters (0–35%), the Mohave Generating Station (<10–18%) and Southern California (1–15%). During winter the Navajo Generating Station (10–25%) and Cholla (3–12%) often contributed the largest fractions. Mean concentrations are much lower, and there are larger fractional declines in contributions from many source areas during winter as compared to summer. These analyses document the successful outcomes that can result from effective regulations.