Chemical Mechanism Research Articles

Sustainable urea treatment by environmental-friendly and highly hydrophilic vesicle-like iron phosphate-based carbon

Despite the versatile potential applications of urea, its unfavorable characteristics for conventional treatment methods hinder its utilization. Therefore, this study developed vesicle-like iron phosphate-based carbon (IP@C400) as a breakthrough urea removal and recovery material for a wide range of urea-containing sources. IP@C400 rapidly exhibited an exceptional capacity (2242 mg/g in 1 h) across a wide range of pH, even in synthetic hemodialysis wastewater with high urea concentrations and diverse co-existing components, compared with the 60 prominent adsorbents. The adsorption process followed dual Pseudo-kinetic, Langmuir-isotherm models with the involvement of primary robust physical (i.e., H-bonding and electrostatic interaction) and chemical mechanisms (i.e., hydrolysis). Remarkably, IP@C400 can maintain high urea removal (90 %) or recovery efficiency (95 %) even after 10 cycles with minimal leakages of Fe and P (far below WHO and EUWFD standards)—a significant improvement over disposable options. IP@C400 could also perform efficiently on batch and a new approach integrating with a naturally accessible material based on the fixed-bed column using low-range urea realistic samples, achieving 65.2 L water over 10 cycles with undetected urea, neutral pH, and well-aligned water safety standards with a minimal adsorbent dose (0.1 g.L−1) and economical cost ($0.05 L-1). Lastly, its environmentally friendly nature, which contains essential nutrients for plant growth, further enhances its recyclability after release. Thus, IP@C400 offers a solution to environmental sustainability and the urgent ultrapure water issue that industries are facing.

Ferroelastic ionic organic crystals that self-heal to 95%

The realm of self-healing materials integrates chemical and physical mechanisms that prevent wear and fracturing and extend the operational lifetime. Unlike the favorable rheology of amorphous soft materials that facilitates efficient contact between fragments, the efficiency of recovery of atomistically ordered materials is restricted by slower interfacial mass transport and the need for ideal physical alignment, which limits their real-world application. We report drastic enhancements in efficiency and recovery time in the self-healing of anilinium bromide, challenging these limitations. Crystals of this material recovered up to 49% within seconds and up to 95% after 100 min via ferroelastic detwinning. The spatial evolution of strain during cracking and healing was measured in real time using digital image correlation. Favorable alignment and strong ionic bonding across the interface of partially fractured crystals facilitate self-healing. This study elevates organic crystals close to the best-in-class self-healing polymers and sets an approach for durable crystal-based optoelectronics.

Numerical Analysis Selecting Chemical Mechanism of Ammonia–Hydrogen Mixture Laminar Burning Velocity by RMSE

AbstractThis study employs Cantera code to investigate the laminar burning velocity of different ammonia–hydrogen mixtures. Suitable models were selected from recent literature, and the one with the lowest root mean square error (RMSE) against experimental data was identified through the error function method. Bao mechanism shows an RMSE value of 4.71 at atmospheric pressure for ammonia–hydrogen mixtures, while the Otomo mechanism exhibits an RMSE of 2.11 under high‐pressure conditions. Additionally, sensitivity analysis was conducted to highlight critical reactions within each mechanism, emphasizing distinctions between different pressures. This approach aims to choose the proper mechanism to reduce computational and experimental costs in the early stages of ammonia–hydrogen research.

Dynamic Metabolic Responses of Resistant and Susceptible Poplar Clones Induced by Hyphantria cunea Feeding.

Poplar trees are significant for both economic and ecological purposes, and the fall webworm (Hyphantria cunea Drury) poses a major threat to their plantation in China. The preliminary resistance assessment in the previous research indicated that there were differences in resistance to the insect among these varieties, with '2KEN8' being more resistant and 'Nankang' being more susceptible. The present study analyzed the dynamic changes in the defensive enzymes and metabolic profiles of '2KEN8' and 'Nankang' at 24 hours post-infestation (hpi), 48 hpi, and 96 hpi. The results demonstrated that at the same time points, compared to susceptible 'Nankang', the leaf consumption by H. cunea in '2KEN8' was smaller, and the larval weight gain was slower, exhibiting clear resistance to the insect. Biochemical analysis revealed that the increased activity of the defensive enzymes in '2KEN8' triggered by the feeding of H. cunea was significantly higher than that of 'Nankang'. Metabolomics analysis indicated that '2KEN8' initiated an earlier and more intense reprogramming of the metabolic profile post-infestation. In the early stages of infestation, the differential metabolites induced in '2KEN8' primarily included phenolic compounds, flavonoids, and unsaturated fatty acids, which are related to the biosynthesis pathways of phenylpropanoids, flavonoids, unsaturated fatty acids, and jasmonates. The present study is helpful for identifying the metabolic biomarkers for inductive resistance to H. cunea and lays a foundation for the further elucidation of the chemical resistance mechanism of poplar trees against this insect.

Novel packed-bed CFD model for pellet combustion: Validation and application to a stove

An advanced CFD (computational fluid dynamics) model has been developed to describe the combustion of wood pellets. It is based on a packed-bed approach and provides a realistic description of the combustion of pellets, resolved in 3D over the whole fuel bed. It considers the properties of the packed bed rather than the properties of the single fuel particles. Compared to a particle-based description, simulation times are shorter due to the reduced complexity. In the model, the local conditions in different parts of the fuel bed (temperatures, flow conditions, oxygen concentrations …) influence the various stages of the combustion process (drying, pyrolysis, charcoal gasification and combustion). The compaction of the fuel bed due to shrinkage of the fuel particles during conversion and the loss of the particle structure shortly before the conversion is complete are also included in the description. The formulation of the bed compaction, the radiation absorption model and the charcoal conversion reactions have been specifically tuned to the combustion of wood pellets. The detailed pyrolysis model includes not only the main components, but also higher hydrocarbon species and tars in a manner specific to the fuel considered. It has been combined with a chemical gas phase mechanism which is a reduction of a detailed mechanism developed for thermo-chemical biomass conversion. The model has been validated against measurement data from a lab-scale batch reactor, and then applied to simulate the fuel bed of a commercial pellet stove. The simulation results are in good agreement with the corresponding measurements.

Enhanced SERS performance of cavity-hosting silver dendrites grown over TiO2 nanotubes

Silver nanostructures, utilized as SERS substrates, consistently exhibit exceptional performance in detecting organic compounds through Raman spectroscopy, primarily due to the electromagnetic enhancement mechanism. This study explores an advanced SERS substrate composed of cavities formed by silver dendrites (Ag-Ds) on TiO2 nanotubes (TiO2-NT), demonstrating exceptional performance in detecting organic compounds through Raman spectroscopy. TiO2-NT acts as a template, guiding the nucleation and growth of Ag-D to create the cavity structures. The deposition time of silver significantly influences substrate performance in detecting Rhodamine 6G (R6G) and Ibuprofen (IB). It has been observed that an extended deposition time diminishes the enhancement factor. In contrast, a shorter deposition time yields notable enhancement due to the combined effects of electromagnetic and chemical enhancement mechanisms. An optimum deposition time limits dendrite growth, forming cavities where the electric field couples with multiple light reflections, further amplifying the SERS enhancement. The cavity-hosted Ag-D/TiO2-NT substrate achieves an impressive analytic SERS enhancement factor of up to 2 × 109, enabling the detection of R6G and IB at a low detection limit of 10-12 M.

Flame stabilization and emission reduction: a comprehensive study on the influence of swirl velocity in hydrogen fuel-based burner design

PurposeThis study aims to numerically analyse a full-scale burner across a wide range of operating pressure conditions and determine the effect of swirl velocity on flame stabilization, flame holding and combustion performance.Design/methodology/approachThis study uses a numerical analysis approach to investigate a three-dimensional full-scale burner. Modified governing equations are used to determine the effect of swirl velocity on flame stabilization and flame holding. The GR-Mech 3.0 chemical reaction mechanism is used to predict the combustion process. To validate the model, a grid independence study is performed.FindingsThe study reveals that swirl velocity enhances flame stability, resulting in better combustion rates. As the swirl velocity increases, higher flame temperatures are observed due to high convective heat recirculation. The heat transfer coefficient and high radiative extinction coefficient are found to vary based on fuel swirl velocity. The mass fraction of CH4 and CO emphasizes the role of swirl velocity on flame structure. Increasing velocity potentially improves combustion by delaying the process, leading to better combustion and lower emissions.Originality/valueThe findings of this study contribute to the understanding of swirl-stabilized combustion and can guide the development of advanced combustion technologies, making it a valuable addition to the existing combustion field.

Carrier-phase direct numerical simulation and flamelet modeling of NOx formation in a pulverized coal/ammonia co-firing flame

A carrier-phase direct numerical simulation (CP-DNS) of a coal/ammonia co-firing flame in a turbulent mixing layer is performed with a detailed chemical reaction mechanism including NOx formation. The combustion characteristics and NOx formation mechanism of the coal/ammonia co-firing flame are investigated in detail through a conditional reaction pathway analysis. A new four-fuel-stream flamelet model is proposed to adapt to the piloted pulverized coal/ammonia co-combustion system, in which the complex mixing among the volatiles, char off-gases, ammonia, and the pilot stream is characterized with four mixture fractions. The flamelet solutions in the fourfold mixture fraction space are transformed into a uniform space to facilitate the access to the flamelet table. The performance of the flamelet model is evaluated through an a priori analysis, a combustion mode analysis, and a chemical timescale analysis. For the turbulent coal/ammonia co-firing flame studied, two distinct flame fronts within the shear layer are observed with the upper part being dominated by ammonia combustion and the lower part being governed by coal combustion. The conditional analyses show that NO species is mainly generated by the lower layer governed by pulverized coal combustion where the nitrogen-containing species from volatile combustion are highly involved in the NO formation. The NO concentration first increases with decreasing the fraction of ammonia in the local computational cell, and then decreases towards pure pulverized coal combustion, which is characterized with a newly introduced manifold coordinate. While the temperature and the major and intermediate species mass fractions in the coal/ammonia co-firing flame can be reasonably predicted by the proposed flamelet model, the NOx species mass fractions are not well predicted in the region where pulverized coal combustion dominates. It is clarified that the inaccurate prediction of the NOx species is not caused by interpolation errors, multiple combustion modes or the kinetics of NOx formation, but mainly attributed to the definition of the progress variable.Novelty and significance statementThe novelty of this research is the first DNS of a coal/ammonia co-firing flame in a turbulent mixing layer, and the proposal of a new flamelet tabulation method for predicting NOx formation in the coal/ammonia co-firing flame. It is significant because• Coal/ammonia co-firing promises to provide continuous, secure power supply at a much reduced carbon footprint compared to pure coal combustion;• The underlying physics governing the coal/ammonia co-firing are analyzed using carrier-phase DNS;• The performance of the newly proposed flamelet model in predicting the NOx species is evaluated based on the DNS dataset.

Dark NO2 Reduction on a Graphene Surface with Implications for Soot Aging and HONO Formation.

Soot, primarily composed of elemental carbon (EC) and organic carbon (OC), is ubiquitous in PM2.5. In the atmosphere, the heterogeneous interaction between NO2 and soot is not only an important pathway driving soot aging but also of central importance to nitrous acid (HONO) formation. It is commonly believed that the surface redox reaction between reductive OC and NO2 dominates the night aging of soot and the conversion of NO2 to HONO. However, completely differing from the currently popular explanation, we find here that the redox reaction between EC and NO2 can also drive the conversion of NO2 to HONO during soot aging. By combining in situ experiments with density functional theory (DFT) calculations, we proposed that the surface carbon vacancy defects on graphite/graphene-like EC should be a type of potential primary adsorption and reactive sites inducing the heterogeneous reduction of NO2. We suggested a new mechanism that NO2 is reduced to form HONO on surface vacancy defects through the splitting of H2O molecules, and the carbon atoms adjacent to surface vacancy are simultaneously oxidized to form hydroxyl-functionalized EC. This novel finding provides insights into the chemical mechanism driving the NO2-to-HONO conversion and rapid soot aging, which expands our knowledge of the heterogeneous chemistry of soot in the atmosphere.

Bio‐inspired 3D Sub‐Microstructures Coupling of Au Nanoparticles for SERS Detection of Trace Fentanyl

Abstract3D surface‐enhanced Raman scattering (SERS) platforms with multi‐dimensional hotspots and better tolerance to laser misfocus show great potential for the rapid detection of trace fentanyl. However, the complex fabrication process of 3D fine structures limits the wide‐ranging application of the SERS technique. Herein, a 3D SERS‐active platform is fabricated utilizing a scalable and cost‐effective strategy that involves the electroless deposition of dense Au nanoparticles on natural butterfly wing scales (b‐wings@Au). The resultant b‐wings@Au proves to be sensitive and reliable, with a lower limit of detection of 4× 10−12 m and an enhancement factor (EFexp) of 1.74 × 108 for fentanyl. Furthermore, it exhibits excellent reproducibility, as evidenced by a relative standard deviation of less than 5%, and also demonstrates outstanding stability. The obtained high EFexp is due to the combined effects of the electromagnetic mechanism, involving the enhanced electromagnetic field generated by 3D periodic hotspots, and the chemical mechanism, involving the charge transfer from fentanyl to Au surface. Additionally, the as‐prepared 3D substrate realizes the trace detection of nine fentanyl analogs. This study provides new ideas for the controllable construction of sensitive SERS platforms for drug detection, ultimately advancing the fields of 3D substrates in booming SERS‐based technologies.

Photo-Assisted Chemical Self-Rechargeable Zinc Ion Batteries with High Charging and Discharging Efficiency.

Chemical self-recharging zinc ion batteries (ZIBs), which are capable of auto-recharging in ambient air, are promising in self-powered battery systems. Nevertheless, the exclusive reliance on chemical energy from oxygen for ZIBs charging often would bring some obstacles in charging efficiency. Herein, we develop photo-assisted chemical self-recharging aqueous ZIBs with a heterojunction of MoS2/SnO2 cathode, which are favorable to enhancing both the charging and discharging efficiency as well as the chemical self-charging capabilities under illumination. The photo-assisted process promotes the electron transfer from MoS2/SnO2 to oxygen, accelerating the occurrence of the oxidation reaction during chemical self-charging. Furthermore, the electrons within the MoS2/SnO2 cathode exhibit a low transfer impedance under illumination, which is beneficial to reducing the migration barrier of Zn2+ within the cathode and thereby facilitating the uniform inserting of Zn2+ into MoS2/SnO2 cathode during discharging. This photo-assisted chemical self-recharging mechanism enables ZIBs to attain a maximum self-charging potential of 0.95 V within 3 hours, a considerable self-charging capacity of 202.5 mAh g-1 and excellent cycling performance in a self-charging mode. This work not only provides a route for optimizing chemical self-charging energy storage, but also broadens the potential application of aqueous ZIBs.

Inspired by nature: Bioluminescent systems for bioimaging applications

Bioluminescence is a natural process where biological organisms produce light through chemical reactions. These reactions predominantly occur between small-molecule substrates and luciferase within bioluminescent organisms. Bioluminescence imaging (BLI) has shown significant potential in biomedical research owing to its non-invasive, real-time observation and quantification. In this review, we introduced the chemical mechanism of bioluminescent systems and categorized several strategies that successfully addressed the native limitations, including improvements on the chemical structures of luciferase-luciferin bioluminescence system and bioluminescence resonance energy transfer (BRET) methods. In addition, we also reviewed and summarized recent advances in bioimaging applications. We hope that this review can provide effective guidance for the development and application of bioluminescent systems in the field of bioimaging.

Non‐Isocyanate Synthesis of Covalent Adaptable Networks Based on Dynamic Hindered Urea Bonds: Sequential Polymerization and Chemical Recycling

AbstractThe development of environmentally sustainable processes for polymer recycling is of paramount importance in the polymer industry. In particular, the implementation of chemical recycling for thermoset polymers via covalent adaptable networks (CANs), particularly those based on the dynamic hindered urea bond (HUB), has garnered intensive attention from both the academic and industrial sectors. This interest stems from its straightforward chemical structure and reaction mechanism, which are well‐suited for commercial polyurethane and polyurea applications. However, a substantial drawback of these CANs is the requisite use of toxic isocyanate curing agents for their synthesis. Herein, we propose a new HUB synthesis pathway involving thiazolidin‐2‐one and a hindered amine. This ring‐opening reaction facilitates the isocyanate‐free formation of a HUB and enables sequential reactions with acrylate and epoxide monomers via thiol–Michael and thiol–epoxy click chemistry. The CANs synthesized using this methodology exhibit superior reprocessability, chemical recyclability, and reutilizability, facilitated by specific catalytic and solvent conditions, through the reversible HUB, thiol–Michael addition, and transesterification processes.

Predicting odor from vibrational spectra: a data-driven approach

This study investigates olfaction, a complex and not well-understood sensory modality. The chemical mechanism behind smell can be described by so far proposed two theories: vibrational and docking theories. The vibrational theory has been gaining acceptance lately but needs more extensive validation. To fill this gap for the first time, we, with the help of data-driven classification, clustering, and Explainable AI techniques, systematically analyze a large dataset of vibrational spectra (VS) of 3018 molecules obtained from the atomistic simulation. The study utlizes image representations of VS using Gramian Angular Fields and Markov Transition Fields, allowing computer vision techniques to be applied for better feature extraction and improved odor classification. Furthermore, we fuse the PCA-reduced fingerprint features with image features, which show additional improvement in classification results. We use two clustering methods, agglomerative hierarchical (AHC) and k-means, on dimensionality reduced (UMAP, MDS, t-SNE, and PCA) VS and image features, which shed further insight into the connections between molecular structure, VS, and odor. Additionally, we contrast our method with an earlier work that employed traditional machine learning on fingerprint features for the same dataset, and demonstrate that even with a representative subset of 3018 molecules, our deep learning model outperforms previous results. This comprehensive and systematic analysis highlights the potential of deep learning in furthering the field of olfactory research while confirming the vibrational theory of olfaction.

Exploration of radical chemistry, precursor sensitivity and O3 control strategies in a provincial capital city, northwestern China

As the core city in northwestern China, Xi'an has suffered from serious O3 pollution in recent years. An observational model, coupled with the Master Chemical Mechanism (V3.3.1) and comprehensive data, analyzed atmospheric oxidation capacity (AOC), O3 formation mechanism, precursor sensitivity and control strategies in Xi'an. The study examined two periods (period I and II), with notable temperature and humidity differences. Despite lower precursor levels in period I, an O3 episode (peak value: 102.68 ppb) occurred only in period I, highlighting the crucial influence of meteorological conditions. Higher removal rate of primary pollutants occurs in period I, but meteorological conditions may not alter the dominant factor of AOC. Period I exhibited markedly high OH reactivity, with aromatics, alkenes, and NOx being the main contributors. HONO photolysis (50.78%) in the morning and O3 photolysis (34.13%) in the afternoon were the main HOx sources in period I, while HONO photolysis (62.86–80.68%) was significant at daytime for period II. Higher temperatures in period I accelerated all reaction rates involved in radical cycling, especially emphasizing RO2 + NO → RO + NO2. The results of sensitivity analysis showed that O3 sensitivity regime is VOC-limited in Xi'an, but the specific reactive species target VOC reductions emissions exhibited discrepancies for two distinct periods. A 20% decrease in VOCs and a 50% decrease in NOx (VOCs/NOx = 0.4) was proposed to be the optimal solution to achieve the O3 control target in period I. This study enhances our understanding of O3 formation under different meteorological conditions and provides scientific evidence for O3 pollution abatement policies in northwestern China, with potential applicability to other cities in this region and similar countries.

Comparative study on the influence of chemical reaction mechanisms on turbulent jet flame

Abstract This paper focus on the influence of chemical reaction mechanisms on the simulation of turbulent jet flame of 11 different chemical reaction mechanisms. These mechanisms are mainly selected from GRI series and their reduced mechanisms, and their reaction kinetics were analyzed. This paper uses LES-TPDF method to simulate Sandia Flame D turbulent jet flame and then analyze the difference of time-averaged temperature, heat release rate and species concentration results in different mechanisms. The results show that the kinetic performance of different chemical mechanisms is very different. The ignition delay time of JL4, SMOOKE and z42 mechanisms are either overestimated or underestimated due to the omission of multi-carbon species and other important species. The differences of the LES results in different mechanisms increase along the axis. The differences near the fuel inlet are mainly due to the difference of kinetic performance, while the difference away from the fuel inlet is more due to the different species and elementary reactions involved in different chemical reaction mechanisms. For all chemical mechanisms, there is a tendency that the more species used in the chemical reaction, the more concentrated the region of high heat release rate, the shorter the flame length, and the higher the maximum temperature throughout the field.

Hypergolic fuel impacting a gelled oxidizer wall: Droplet dynamics, heat release, ignition, and flame analysis

The combination of high-concentration solutions of hydrogen peroxide, known as High Test Peroxide (HTP), with the green fuel composed of tetramethylethylenediamine, dimethylaminoethanol, and methanol (TMEDA/DMEA/MeOH, 1:1:1 vol%), catalyzed by 1 wt% of copper chloride dihydrate, has significant potential for space hypergolic propulsion applications in terms of performance and safe operation. Besides the well-known and mature propulsion systems adopting liquid and solid propellants, gel propellants also present interesting characteristics that can be better explored to enable the creation of alternative propulsive systems. The present work employed HTP at 98 wt% with 6 wt% of fumed silica as a gelling agent to create gelled HTP (GHTP). Droplets of the green fuel impinged on a layer of GHTP placed over a glass slide, acting as a solid oxidizer, mimicked an element of a new hybrid gel/liquid hypergolic propulsion system. Data from infrared and visible light cameras enabled a detailed analysis of the dynamics of a reactive droplet impinging on a gelled oxidizer wall, as well as the heat release, ignition, and flame spread of the hypergolic GHTP/green fuel pair under open-air conditions. The heat release was observed to be distributed across concentric annular areas for both the fuel surrogate and the fuel with catalyst, before and after ignition, demonstrating a strong correlation with non-reactive droplet fluid dynamics, which was corroborated by spread diameter analysis processed from visible image data. Vapor and Ignition Delay Times (VDT and IDT) were found to be as low as 4 and 17 ms, respectively, for the highest droplet impact velocity and catalyst concentration. The reaction rate in the gas phase, considering the flame spread area, showed a dependency of both impact velocity and catalyst concentration, with the latter exhibiting a more pronounced and clear effect. The surface temperature ranges where first vaporization and ignition occurred were 60 °C ∼ 70 °C and 120 ∼ 170 °C, respectively, which is close to the boiling point of methanol and the auto-ignition temperature of TMEDA. This finding, along with the chemical mechanisms in the gas phase related to the presence of a catalyst in the fuel, may be important for hypergolic ignition. The relatively low ignition temperatures and the short ignition times represent additional advantages of the present hypergolic combination for propulsion applications.

Performance and mechanism of chitosan-modified La-based MOF nanocomposites for high-efficiency adsorption of azo anion dye Congo red

The impact of organic dye wastewater discharge on the environment cannot be ignored following the development of modern industry. The adsorption method is widely used in wastewater treatment owing to its low cost and environmental friendliness. Improving the application performance of adsorption materials is the key to technical optimization. Herein, a lanthanum-based metal organic framework (La-BDC) and its derivative loaded with chitosan (La-MOF@CS) were synthesized with the solvothermal method, and the adsorption behavior and mechanism of anionic dye Congo red (CR) were studied. The experimental adsorption capacities of La-BDC and La-BDC@CS for 100 mg·L-1 CR at 25 ℃ were 260.46 and 227.82 mg·g−1, respectively, and maintained stable in a wide pH range and under different water quality conditions. The results of adsorption kinetics and adsorption isotherm showed that the adsorption process conformed to the pseudo-second-order kinetics and Langmuir model. The saturated adsorption capacities of the two materials were as high as 2249.56 and 2041.07 mg·g−1, respectively. La-BDC@CS maintained more than 95 % of the original adsorption capacity after ten cycles, which has practical application potential. Mechanism experiments show the adsorption of CR by La-BDC@CS is synergistically caused by various chemical mechanisms, such as hydrogen bonding, electrostatic attraction, and π-π coordination.

Interactions between volatile air pollutants and atmospheric water production – Effects of chemical properties, mechanisms, and transfer processes

Regional water scarcity is among the most urgent challenges of global climate change. Atmospheric water harvesting is a promising method to mitigate these challenges, and the atmospheric water generator (AWG) is already an established technology. Although this method can produce over 10,000 L of water per day, the water's quality has not been studied in depth. Air pollutants, especially volatile organic compounds (VOCs), are potential contaminants of water produced from air. We evaluated the chemical and physical parameters of different VOCs that might influence their ability to be transferred from air to AWG water. Our findings strongly suggest that the ability to form hydrogen bonds is a key factor in this transfer. Henry's law constant, polarity, and intrinsic solubility were the main predictors of a VOC's transfer to AWG water. Hence, aliphatic or aromatic compounds (such as benzene or octane) were not found at significant concentrations in AWG water (e.g. above WHO guidelines), whereas ammonia and alcohol compounds were. This should be taken into consideration when analyzing potential contaminants in harvested atmospheric water. The condensation process itself was also found to enhance the transfer of VOCs into water droplets, and higher relative humidity (%RH) also increased VOC transfer. Gas-phase infrared spectrum analysis of VOCs at different %RH revealed possible interactions between water vapor and specific VOCs in the air. However, our main conclusion from this study is that VOC transfer from the air into AWG water occurs predominantly via dissolution in the condensed droplets, and strongly depends on their chemical properties of polarity and hydrogen-bond formation.

Chemical characteristics, sources, and formation mechanisms of PM2.5 before, during, and after the Spring Festival in a plateau city of Southwest China

To study chemical characteristics, sources and formation mechanisms of PM2.5 during the Spring Festival (SF), 39 elements, 9 water–soluble ions (WSIs) and 8 fractions of carbonaceous species in PM2.5 and PM10 at two sites in Kunming were investigated. The results indicated that the average mass concentration of PM2.5 and PM10 were 61.03 ± 25.11 and 80.48 ± 30.08 μg/m3 in the urban area, and 18.96 ± 4.66 and 56.76 ± 21.69 μg/m3 in the suburban area, respectively. Concentrations of PM2.5 peaked significantly on the Chinese New Year (NYE) and the Lantern Festival (LF) in the urban area. Compared to the previous day of NYE, Ba and Sr concentrations increased by 22.1 and 39.2 times in urban areas, and by 6.5 and 8.3 times in suburban areas. The sum of sulfate, nitrate, and ammonium (SNA) accounted for 82.03% and 60.38% of WSIs in urban and suburban areas, respectively. The most abundant carbonaceous species in urban and suburban areas were OC3 and EC1. According to the Positive Matrix Factorization (PMF) calculation, secondary formation (41.76%) was the predominant sources of PM2.5, and the contribution of fireworks to PM2.5 was 9.06%. The formation of secondary organic carbon (SOC) occurred through heterogeneous reactions. SNA was derived from heterogeneous reaction and photochemical reaction.