Fraction Of Large Particles Research Articles

Shape effects in binary mixtures of PA12 powder in additive manufacturing

The quality of powder spread in additive manufacturing devices depends sensitively on particle shapes. Here, we study powder spreading for mixtures of spherical and irregularly shaped particles in Polyamide 12 powders. Using DEM simulations, including heat transfer, we find that spherical particles exhibit better flowability. Thus, the particles are deposited far ahead of the spreading blade. In contrast, a large fraction of non-spherical particles hinders the flow. Therefore, the cold particles are deposited near the front of the spreading blade. This results in a temperature drop of the deposited particles near the substrate, which cannot be seen with spherical particles. The particles of both shapes are homogeneously distributed in the deposited powder layer.

Impact of meteorological parameters on black carbon mass concentrations over Silicon City “ Bengaluru, Southern part of India” – A Case Study

In the context of Bengaluru, the impact of black carbon (BC) aerosols on regional climate dynamics emerges as a crucial area of investigation. Due to the lack of high-resolution BC data, it was collected at 5 different locations in Bengaluru, Karnataka, from January 2019 to December 2019. The mean mass concentration of BC was 5.91 microg m-3, whereas the higher mass concentration of BC was 7.71 microg m-3 over the city railway station and the lower (3.69 microg m-3) was in Jayanagara. The contribution of BC in higher-traffic and industrial locations was approximately 41% higher than the residential locations, which indicates a large fraction of soot particles are from anthropogenic activities mainly from fossil fuel combustion. The seasonal concentrations of BC have also exhibited a large variability, with the highest sequence in magnitude during the winter season (9 microg m-3) followed by the summer (6.3 microg m-3), post-monsoon (5.8 microg m-3) and monsoon (3.4 microg m-3) seasons during the study period. The concentrations of BC during the monsoon season were very low as compared to the winter season due to the impact of the washout effect. The BC was negatively significantly correlated (-0.70) with rainfall indicating the washout effect, however, during the winter season, it was due to impact of boundary layer condition. Overall (annually) the mean concentrations of BC have increased by around 55% within five years over the urban region, which indicates the impact of man-made activities. The higher mass concentration of BC over Bangalore in the southern part of India, indicates serious implications for the regional climate that need to be investigated and mitigated. Finally, the study suggests that immediate action is required to mitigate the emission of BC into the urban environment in the southern part of India.

Aerosol mixing state, new particle formation, and cloud droplet number concentration in an urban environment

Anthropogenically derived aerosols have been hypothesized to influence convective precipitation by increasing the available pool of cloud condensation nuclei. Here, we present a synthesis of aerosol size distribution and subsaturated hygroscopicity measurements between 15 and 250 nm diameter particles during the TRacking Aerosol Convection interactions ExpeRiment (TRACER). We found that the aerosol is externally mixed and can be described by a quasi-two-component description comprising a more and less hygroscopic mode. The mean hygroscopicity parameters for these modes across all sizes were 0.03 ± 0.04 and 0.22 ± 0.08 with no significant dependence on particle size. The number fraction of the more hygroscopic mode is 40 % for particles between 15 and 40 nm and gradually increases to ~70 % for particles >100 nm. Winds from the southerly direction feature particles with larger hygroscopicity parameters and have a larger fraction of particles in the more hygroscopic mode. The hygroscopicity parameter exhibits diurnal cycles that are consistent with condensation of a species with a hygroscopicity parameter ~0.1 which corresponds to values expected for secondary organic aerosol. We also identified nine small particle events that were attributed to particle formation by nucleation. The data are consistent with new particle formation having occurred aloft, followed by downward mixing with daytime turbulence. The species that are responsible for modal growth had hygroscopicity parameters varying between 0.05 and 0.34. These values systematically depended on the wind sector, suggesting that the chemical composition of the precursors differed. Hourly cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) values derived from the aerosol size distribution, subsaturated hygroscopicity measurements, and adiabatic parcel model simulations showed a dynamic range of a factor of 2–3 in CDNC depending on the wind sector, with lower values associated with southerly onshore flow.

Prolonged Dark Chemical Processes in Secondary Organic Aerosols on Filters and in Aqueous Solution.

Secondary organic aerosol (SOA) represents a large fraction of atmospheric aerosol particles that significantly affect both the Earth's climate and human health. Laboratory-generated SOA or ambient particles are routinely collected on filters for a detailed chemical analysis. Such filter sampling is prone to artifactual changes in composition during collection, storage, sample workup, and analysis. In this study, we investigate the chemical composition differences in SOA generated in the laboratory, kept at room temperature as aqueous extracts or on filters, and analyzed in detail after a storage time of a day and up to 4 weeks using liquid chromatography coupled to high-resolution mass spectrometry. We observe significantly different temporal concentration changes for monomers and oligomers in both extracts and on filters. In SOA aqueous extracts, many monomers increase in concentration over time, while many dimers decay at the same time. In contrast, on filters, we observe a strong and persistent concentration increase of many dimers and a decrease of many monomers. This study highlights artifacts arising from SOA chemistry occurring during storage, which should be considered when detailed organic aerosol compositions are studied. The particle-phase reactions on filters can also serve as a model system for atmospheric particle aging processes.

Accelerating the dissolution and transformation of detrimental Fe-rich intermetallics in recycled Al-Mg-Si alloy by homogenization and hot deformation

The plate-like Fe-rich intermetallics in recycled Al-Mg-Si alloys dramatically degrade the mechanical properties, which has to be minimized to obtain the high-performance components. Previous finding of using Mn to neutralize the harmful Fe have proven to be effective at a Mn:Fe ratio of 2:1 in order to convert detrimental β-Al5FeSi (β-Fe) plates into less harmful α-Al₁₅(Fe, Mn)₃Si₂ (α-Fe) scripts. However, excess amount of Mn will inevitably introduce large fraction of intermetallic particles which reduce the ductility of alloy. In this study, we propose a new process which utilize both homogenization and hot deformation processes to achieve dissolution and transformation of detrimental Fe-rich intermetallics. The transformation mechanisms with limited Mn addition (Mn:Fe Ratio≈1) have been uncovered. After homogenization for 10 h, the percentage of β-Fe decreases from 1.13% to 0.87%. After 30% hot deformation, it further decreases to 0.45% and the elongation is increased by 55.97%. If we combine the hot deformation 30% with cold deformation by 20%, it will eventually decrease to 0.25%, achieving complete conversion from β-Fe to α-Fe, and the tensile strength is increased by 42.15%. To uncover the transformation mechanisms of Fe-rich intermetallics, 3D distribution of Fe-rich intermetallics and microporosity have been quantified as a function of processing conditions by using X-ray computed tomography (XCT), demonstrating that the new approach can make use of the Fe tolerable recycled Al alloys to achieve high strength and ductility.

Insight into the interfacial microstructure and chemistry of hot isostatically pressed AA6061-AA6061 bonds for U-10Mo fuel cladding application

Hot isostatic pressing (HIP) is performed on AA6061-AA6061 plates for U-10Mo monolithic fuel cladding application and this process allows us to bond multiple plates and large surface areas in a single run. In the current work, we HIP'd several plates of AA6061 with different HIP can dimensions at 560 °C and 103 MPa for 90 min to gain insight into the interfacial microstructure, chemistry and eventually bond strength. Interfacial microstructure characterizations were performed using scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) in conjunction with Transmission electron microscopy (TEM) to quantify precipitate fractions and study recrystallization, grain growth, and orientation relationships across the interface. Microstructural analyses revealed the precipitation of a large fraction of Mg2Si particles and a ∼50 nm thick Al-Mg oxide layer at the interface. Further TEM analysis confirmed that the oxide layer was not continuous, and Mg2Al2O5 oxide particles with an average size of 18 nm were present in the oxide layer. The bond strength of HIP-processed samples was correlated with peel testing and the bond strength was determined to be a direct function of the Mg2Si particle size at the interface. Finite element modeling analysis was performed to study the HIP can cooldown rate after HIP processing and was correlated with the interface precipitation.

ASSESSMENT OF SPECIFIC SURFACE AREA AND POROSITY OF SUBSOILS

Soils and subsoils have a complex structure consisting of several elements with different morphology and chemical composition, combining micro-, meso-, and macroporous substructures. Classical approaches, such as Brunauer-Emmett-Teller (BET) or Barrett-Joyner-Halenda (BJH) methods, cannot provide an accurate assessment of morphological characteristics of such solids, nor can do modern sophisticated numerical methods which depend on idealized models of pores that hardly reflect a real morphology of heterogeneous solids in question. The present study describes a way to overcome this difficulty by applying a combination of the αS-plot technique and a modified Remy-Poncelet method. The proposed approach allowed estimating the volumes of the untramicropores, supermicropores and the sum of meso- and macropores as well as the specific surface areas of the solid without ultramicropores and of the solid without all micropores. The former specific surface area is a more reasonable estimate of the area available for layer coverage than the BET specific surface area, and all together these characteristics provide a detail description of solid’s morphology. Subsoil samples excavated from different depths were used as exemplary solids. They mostly consisted of quartz, feldspar, and clay minerals and had different sorts of pores associated with the clay fraction and soil aggregates as well as a relatively large fraction of non-porous sand particles. Relations of the morphological properties with subsoil profile and mineralogical composition are discussed. For citation: Asnin L.D., Samoylov M.S., Pershina M.V., Tselishchev Yu.G., Sliusar N.N. Assessment of specific surface area and porosity of subsoils. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 6. P. 55-64. DOI: 10.6060/ivkkt.20246706.6996.

Commercial plant protein isolates: The effect of insoluble particles on gelation properties

Commercial plant protein isolates generally contain a substantial fraction of large insoluble protein particles. We study how these affect the gelation properties of heat-induced protein gels (15% w/w protein, pH 7) and used homogenization as a mean to reduce the particle size of the insoluble fraction before gelation. Three different commercial plant proteins were studied as models for isolates differing in dispersibility and size of insoluble protein particles: Fava bean (FBPI), Pea (PPI) and Mung bean (MBPI). As expected, homogenization (50 MPa, 2 cycles) reduced the particle size and improved the dry matter dispersibility of protein dispersions. We found that the (shear) storage modulus G’ and critical shear strain for fracture of gels obtained after heating were not consistently impacted by homogenization. In contrast, fracture properties in uniaxial compression were sensitive to homogenization, with homogenization leading to gels that are more resistant to fracture. Gels obtained from the isolate with the smallest fraction of insoluble particles and still contained native proteins, FBPI, were the most fracture resistant. Fluorescence microscopy indicated that the insoluble fraction remained well-dispersed in the matrix after heat-induced gelation and that homogenization led to a more homogeneous appearance of the protein networks, with smaller particles being homogeneously dispersed in the continuous background. We conclude that mechanically breaking down insoluble particles in commercial plant protein isolates contributes strongly to their functionality by reducing the number of large insoluble particles that act as effective nucleation points for hydrogel fracture.

Evaluation of methods for characterizing the fine particulate matter emissions from aircraft and other diffusion flame combustion aerosol sources

The U. S. Environmental Protection Agency in collaboration with the U. S. Air Force Arnold Engineering Development Complex conducted the VAriable Response In Aircraft nvPM Testing (VARIAnT) 3 and 4 test campaigns to compare nonvolatile particulate matter (nvPM) emissions measurements from a variety of diffusion flame combustion aerosol sources (DFCASs), including a Cummins diesel engine, a diesel powered generator, two gas turbine start carts, a J85-GE-5 turbojet engine burning multiple fuels, and a Mini-CAST soot generator. The VARIAnT research program was devised to understand reported variability in the ARP6320A sampling system nvPM measurements. The VARIAnT research program has conducted four test campaigns to date with the VARIAnT 3 and 4 campaigns devoted to: (1) assessing the response of three different black carbon mass analyzers to particles of different size, morphology, and chemical composition; (2) characterizing the particles generated by 6 different combustion sources according to morphology, effective density, and chemical composition; and (3) assessing any significant difference between black carbon as determined by the 3 mass analyzers and the total PM determined via other techniques. Results from VARIAnT 3 and 4 campaigns revealed agreement of about 20% between the Micro-Soot Sensor, the Cavity Attenuated Phase Shift (CAPS PMSSA) monitor and the thermal-optical reference method for elemental carbon (EC) mass, independent of the calibration source used. For the LII-300, the measured mass concentrations in VARIAnT 3 fall within 18% and in VARIAnT 4 fall within 27% of the reference EC mass concentration when calibrated on a combustor rig in VARIAnT 3 and on an LGT-60 start cart in VARIAnT 4, respectively. It was also found that the three mass instrument types (MSS, CAPS PMSSA, and LII-300) can exhibit different BC to reference EC ratios depending on the emission source that appear to correlate to particle geometric mean mobility diameter, morphology, or some other parameter associated with particle geometric mean diameter (GMD) with the LII-300 showing a slightly stronger apparent trend with GMD. Systematic differences in LII-300 measured mass concentrations have been reduced by calibrating with a turbine combustion as a particle source (combustor or turbine engine). With respect to the particle size measurements, the sizing instruments (TSI SMPS, TSI EEPS, and Cambustion DMS 500) were found to be in general agreement in terms of size distributions and concentrations with some exceptions. Gravimetric measurements of the total aerosol mass produced by the various DFCAs differed from the reference EC, BC and integrated particle size distribution measured aerosol masses. The measurements of particle size distributions and single particle analysis performed using the miniSPLAT indicated the presence of larger particles (≳150 nm) having more compact morphologies, higher effective density, and a composition dominated by OC and containing ash. This increased large particle fraction is also associated with higher values of single scattering albedo measured by the CAPS PMSSA instrument and higher OC measurements. These measurements indicate gas turbine engine emissions can be a more heterogeneous mix of particle types beyond the original E−31 assumption that engine exit exhaust particles are mainly composed of black carbon.

Differentiation of prokaryotic community composition in suspended sediment size-fractionation in a small loess watershed

The transfer of particle-bound prokaryotes and substrates from slopes to rivers during soil erosion is a crucial dynamic process that greatly influences terrestrial biological and geochemical cycles. Particle size strongly affects the transport distance of suspended sediments and likely induces prokaryote and substrate variations along the course of the river. Previous studies have mainly focused on the spatial redistribution of soil prokaryotes, whereas the variation in prokaryotic diversity and community composition among different particle size-fractions in suspended sediments remain unclear. In this study, suspended sediments were collected at four plots (upstream, middle stream, downstream, and dam) along a river that runs through a valley. Sampled sediments were size-fractionated into > 63 μm and < 63 μm particles (referred to as small and large particle fractions hereafter), to identify the corresponding prokaryotic community composition, interactions, and functions. The richness index (Chao1 and observed species) and the diversity index (Shannon) of sediment-associated prokaryotic communities significantly decreased from upstream towards dam plots, except in the small particle fraction in downstream and dam plots. The highest β-diversity index value was found for the large particle fractions, while the geospatial contribution to β-diversity varied. The concentration of Proteobacteria in downstream (41.39 %) and dam (34.86 %) plots was lower than that in the upstream (47.65 %) and middle stream (45.90 %) plots. In contrast, Cyanobacteria (4.89 % and 6.75 %) and Verrucomicrobiota (5.98 % and 11.00 %) concentrations were greater in the downstream and dam plots, respectively, than those in the upstream (0.93 % and 2.43 %) and middle stream (3.37 % and 3.11 %) plots, respectively. Additionally, the concentrations of Verrucomicrobiota and Bacteroidota were significantly higher in the small particle fractions (2.26–8.12 % and 4.33–7.72 %) than those in the large particle fractions (2.03–5.94 % and 3.70–7.11 %). Compared to the other plots, upstream plots had a larger clustered network and a greater number of co-occurrences within the prokaryotic community in the bulk sediment and in the small particle fraction, whereas more complex interactions among prokaryotic communities were found in the large particle fraction from the dam plots. Soil organic carbon (SOC), total nitrogen (TN), and Olsen phosphorus were the three most influential factors, explaining 67.41 % of the variation in prokaryotic community. Proteobacteria and Myxococcota correlated negatively with SOC, TN, and Olsen P but positively with C = O. Conversely, Cyanobacteria and Verrucomicrobiota correlated positively with SOC, TN, and Olsen P but negatively with C = O. Functional groups linked to the biogeochemical cycling of carbon (methanol oxidation and methylotrophy) were found in high concentrations, whereas those linked to nitrogen (nitrogen and nitrate respiration) were found in low concentrations in upstream and middle stream plots. Reassembly of the sediment physicochemical characteristics among geospatial plots along the transport transect significantly altered the prokaryotic community composition and metabolic functional groups.

Simultaneous Optical and Electrical Monitoring of Charge Percolation in Flow Electrodes

Electrochemical reactions are limited to the surface of the electrode, which makes the construction and intensification of electrochemical processes challenging. To increase the space-time yield of electrochemical cells, the electrochemically active surface area has to be enlarged. This can be achieved by either increasing the surface of a fixed electrode (e.g., porous electrodes) or by so-called flow electrodes. Flow electrodes consist of conductive particles suspended in the electrolyte. They have the advantage of increasing the active surface area of the electrode and also enabling continuous recycling and exchange of the active electrode material. They have been successfully applied, for example, for energy storage in redox flow batteries and desalination in flow-electrode capacitive deionization (FCDI).In flow electrodes the conductive particles dynamically increase the active area of the electrode by collision with the electrode; however, the exact mechanism of charge transport in such suspensions, also called charge percolation, is not completely understood. Yet, the successful implementation of flow electrodes in electrochemical processes requires a deeper understanding of how these particles interact within the electrochemical system. Charge percolation in flow electrodes is highly dynamic, and the conductivity of the suspensions depends on multiple factors like the amount and position of the particles, the shape and accessibility of the current collector, and especially the contact between particles and current collector. Literature presents different approaches which deal with charge transport in conductive suspensions, either by analyzing the electrical properties of flow electrodes in flow or by examining the structure and position of the particles visually in static conditions. We combine visual and electrical in-situ monitoring of charge percolation events in a single experimental setup. We developed a transparent electrochemical flow cell, made of transparent polydimethylsiloxane (PDMS), allowing for in-situ measurements. A constant voltage is applied to the current collector by a potentiostat. The resulting electrical current is measured simultaneously by recoding the particle movements using an optical microscope and a high-speed camera. The design of the electrochemical cell enables different positions of the particles within the channel in different flow modes: Contact between particles and the current collector can be either prevented or enforced. A motion-tracking algorithm analyses the videos to determine the area of particles in the electric field and the area of particles contacting the current collector. This allows for the correlation of particle behavior and electrical current.We investigated the influence of electrolyte, particle fraction, and the contact probability of particles and current collector on charge transport. Our results show that contact between particles and the current collector is a main contributor to charge transport in flow electrodes. But particles cluster can also increase the current, even if they do not touch the current collectors. The highest increase in current was achieved for large particle fraction short circuiting both current collectors. These results show that the way the particle suspension interacts with the electrode and by guiding the flow the electrochemical processes can be improved dramatically.

Temperature- and Size-Dependent Photoluminescence of CuInS2 Quantum Dots.

We present the results of a temperature-dependent photoluminescence (PL) spectroscopy study on CuInS2 quantum dots (QDs). In order to elucidate the influence of QD size on PL temperature dependence, size-selective precipitation was used to obtain several nanoparticle fractions. Additionally, the nanoparticles' morphology and chemical composition were studied using transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The obtained QDs showed luminescence in the visible-near infrared range. The PL energy, linewidth, and intensity were studied within an 11-300 K interval. For all fractions, a temperature decrease led to a shift in the emission maximum to higher energies and pronounced growth of the PL intensity down to 75-100 K. It was found that for large particle fractions, the PL intensity started to decrease, with temperature decreasing below 75 K, while the PL intensity of small nanoparticles remained stable.

Effect of driving characteristics and ambient temperature on the particle emissions during engine restart of spark ignition hybrid electric vehicle

In this study, we analyzed particle emission characteristics in the engine restart (ER) phase of a hybrid electric vehicle (HEV) based on driving characteristics and ambient temperature. The ambient temperature was set at intervals of 10 °C from − 10 °C to 20 °C. ES-582.1, PPS-M, EEPS, and temperature sensors were installed to acquire hybrid control unit (HCU), particle number (PN), PN size distribution, and exhaust temperature data. The on board test route was conducted in the South Korean real driving emissions (RDE) certification route, consisting of urban, rural, and motorway phases. The test HEV was controlled by dividing the engine operation during driving into ER and normal phases. Within 5 s immediately after ER, it emitted PN equivalent to 90% of the total test emissions. The count of ER was higher in urban phases compared to rural and motorway phases. As the ambient temperature decreased, PN emissions increased regardless of the driving mode, but the ER PN percent decreased. Immediately after ER, PN emissions increased rapidly, peaked at around 2–3 s, and then decreased thereafter. The average engine-off time before ER was the longest in the urban phase, and the average ER exhaust temperature was the highest in the motorway phase. The size fraction of large particles increased as the ambient temperature decreased.

Transport and deposition behaviors of graphite aerosol in the steam generator building during an overpressure discharge accident of HTR-PM

The water-ingress accident is one of design basis accidents of high-temperature gas-cooled reactors (HTGR). The rapid change of the flow field and the direct brush of the high-velocity gas flow may cause a large fraction of graphite dust to resuspend, which is further discharged into the steam generator building when the overpressure relief protection is triggered. Due to the coupling with the radioactive fission products (FPs), the behaviors of the discharged particles are crucial for the reactor safety analysis and source-term evaluation in the overpressure discharge scenario. In this work, we numerically investigate the transport, deposition and releasing behaviors of graphite aerosol in the full-scale steam generator building of HTR-PM by the Eulerian-Lagrangian method. The mixture-ideal-gas law is used for describing the mixture between helium and air, and the CFD-DPM scheme is employed for tracking the trajectory and velocity of individual particles. Particularly, the effects of the irregular shape on the particle-fluid and particle-wall interactions are included. The simulation results show the particles are quasi-uniformly distributed in the steam generator building and the deposition and releasing rates with the time follow the exponential relationship at the late-stage. The distribution of all the deposited, escaped and airborne particles are analyzed. Due to the strong thermophoretic effect, a large fraction of particles are deposited on the cold walls. The extrapolation by the exponential relation indicates a final releasing fraction of 18.94%. Compared to the current conservative assumption that all the dust particles in the steam generator building will eventually enter the environments, our results demonstrate that the steam generator building of HTR-PM still has certain capability to retain the graphite dust during an overpressure discharge accident scenario.

Small angle X-ray scattering of particle growth and structure in spray flame synthesis

Customized metal oxide nanoparticles are on increasing demand due to their high specific surface area coupled with their material properties. Spray flame synthesis (SFS) is able to produce such particles in high quantity and purity. However, the turbulent flame including droplets is a complex system. The analysis of the product is challenging due to the broad size distribution of the aggregated primary particles. Thus, this study combines small angle X-ray scattering (SAXS) with transmission electron microscopy (TEM) in order to gain valuable information about primary particle sizes and fractal properties. Insights about the particle formation is obtained by comparing the SAXS data of titanium oxide and iron oxide particles produced with a variety of precursors in different concentrations using two burner setups. Remarkably, all presented systems show a size distribution of the primary particle with two size fractions. The differences in the sizes and consequences for the gained information about the fractal dimensions are discussed in detail. This includes the overlap of scattering information and resolution limits. All particle structures include small particles of 5–8 nm pointing to a gas-to-particle pathway. The large particle fraction ranges from 35 to 320 nm depending on precursor composition and concentration. Their formation is likely linked to hydrolysis reactions of the precursor in spray droplets. For the aggregates, the fractal dimension of mass with values 1.6–1.8 point to diffusion-limited cluster aggregation which is typical for flame-made products. The evaluation of in situ studies with synchrotron radiation confirms the gas-to-particle pathway.

Process-property correlations for spherical composite Al·Ti powders prepared by emulsion-assisted milling

Spherical composite powders desired in many applications can be produced using emulsion-assisted milling. This study is focused on finding correlations between the milling process parameters and characteristics of the produced spherical powders. A composite Al·Ti powder served as the test material system. Spherical powders were prepared using a planetary mill and using an emulsion formed by hexane and acetonitrile as continuous and droplet phases, respectively. Milling conditions including the ratio of immiscible liquids (LR), ball to powder mass ratio (BPR), rotation rate (RPM) and milling time were varied. Optical microscopy images of the powders produced served to recover descriptors of the product particle shapes and sizes. Analysis of the generated image-based data enabled classification of the produced powders, separating spherical and nonspherical particles. This made it possible to recover characteristics of spherical particles, which were correlated with the milling conditions. The quality of the produced spherical powders was assessed using a parameter, Q, maximized when a large fraction of spherical particles with the narrowest size distribution was produced. A correlation was found between Q and a compounded milling process parameter taken as product of grouped parameters: X=BPR∙RPM∙time, Y=BPR∙RPM∙LR, and Z=RPM/BPR, each raised in a separate power, x, y, and z, respectively. The correlation formed a maximum around the conditions leading to formation of the spherical powders with the best quality (highest Q). For the same milling conditions, for which the highest quality spheres were formed, the refinement of the material was maximized, based on the smallest crystallite sizes for both Al and Ti.

Amino acids, carbohydrates, and lipids in the tropical oligotrophic Atlantic Ocean: sea-to-air transfer and atmospheric in situ formation

Abstract. This study examines carbohydrates, amino acids, and lipids as important contributors to organic carbon (OC) in the tropical Atlantic Ocean at the Cape Verde Atmospheric Observatory (CVAO). The above compounds were measured in both surface seawater and in ambient sub-micron aerosol particles to investigate their sea-to-air transfer, including their enrichment in the sea surface microlayer (SML), potential atmospheric in situ formation or degradation, and their oceanic contribution to the ambient marine aerosol particles. In bulk seawater and the SML, similar distributions among species were found for the lipids and carbohydrates with moderate SML enrichments (enrichment factors EFSML = 1.3 ± 0.2 and 1.1 ± 0.5 respectively). In contrast, the amino acids exhibited a higher enrichment in the SML with an average EFSML of 2.3 ± 0.4, although they are less surface-active than lipids. The same compounds studied in the seawater were found on the ambient sub-micron aerosol particles, whereas the lipids' enrichment was more pronounced (EFaer.=1.6×105) compared to the amino acids and carbohydrates (EFaer.=1.5×103 and 1.3×103 respectively), likely due to their high surface activity and/or the lipophilic character. Detailed molecular analysis of the seawater and aerosol particles revealed changes in the relative abundance of the individual organic compounds. They were most pronounced for the amino acids and are likely related to an in situ atmospheric processing by biotic and/or abiotic reactions. On average, 49 % of the OC on the aerosol particles (=∧97 ng m−3) could be attributed to the specific components or component groups investigated in this study. The majority (43 %) was composed of lipids. Carbohydrates and amino acids made up less than 1 % of the OC. This shows that carbohydrates, at least when resolved via molecular measurements of single sugars, do not comprise a very large fraction of OC on marine aerosol particles, in contrast to other studies. However, carbohydrate-like compounds are also present in the high lipid fraction (e.g. as glycolipids), but their chemical composition could not be revealed by the measurements performed here. Previously determined OC components at the CVAO, specifically amines, oxalic acid, and carbonyls, comprised an OC fraction of around 6 %. Since the identified compounds constituted about 50 % of the OC and belong to the rather short-lived biogenic material probably originating from the surface ocean, a pronounced coupling between ocean and atmosphere was indicated for this oligotrophic region. The remaining, non-identified OC fraction might in part contain recalcitrant OC; however, this fraction does not constitute the vast majority of OC in the aerosol particles investigated here.

In Situ Observation of Multiphase Oxidation-Driven Secondary Organic Aerosol Formation during Cloud Processing at a Mountain Site in Southern China

Secondary organic aerosols (SOAs) account for a large fraction of atmospheric fine particles, but the mechanisms of their formation and evolution processes remain unclear. In this study, a ground-based counterflow virtual impactor was used in combination with an online time-of-flight aerosol chemical speciation monitor to investigate the multiphase (gaseous and aqueous) oxidation processes and the SOA influencing factors during cloud events at a mountain site in southern China. Our results showed that the clouds promoted the formation of low-oxidized oxygenated organic aerosol (LO-OOA) and more-oxidized oxygenated organic aerosol (MO-OOA). At night, ozone (O3) and nitrate radicals (NO3•) oxidized volatile organic compounds (VOCs, mostly biogenic VOCs) to the precursors of LO-OOA and were absorbed in the cloud droplets to form LO-OOA, while the hydroxyl radical (•OH) was the main oxidant for LO-OOA during daytime. In the cloud droplets, LO-OOA was further oxidized by •OH to form MO-OOA. We propose that isoprene can be oxidized to form products in the gas phase and then absorbed by acidic cloud droplets to form 2-methylglyceric acid (2-MG), 2-MG-organosulfate, and 2-MG-organonitrate. This study improves our understanding of SOA formation, driven by multiphase oxidation during cloud events.

Preferential association of polycyclic aromatic hydrocarbons (PAHs) with soil colloids at an e-waste recycling site: Implications for risk of PAH migration to subsurface environment

Polycyclic aromatic hydrocarbon (PAH) contamination at e-waste recycling sites poses high ecological and human-health risks. Of note, PAHs in surface soils can be mobilized through colloid-facilitated transport, and may migrate into the subsurface and pollute groundwater. Here, we show that the colloids released from the soil samples at an e-waste recycling site in Tianjin, China contain high concentrations of PAHs, with total concentrations of 16 PAHs as high as 1520 ng/g dw. Preferential association of the PAHs with the colloids is observed, with the distribution coefficients of PAHs between colloids and bulk soil often above 10. Source diagnostic ratios show that soot-like particles are the main source of PAHs at the site, due to the incomplete combustion of fossil fuels, biomass, and electronic wastes during the e-waste dismantling practices. Due to their small sizes, a large fraction of these soot-like particles can be remobilized as colloids, and this explains the preferential association of PAHs with colloids. Moreover, the colloids-soil distribution coefficients are higher for the low-molecular-weight PAHs than for the high-molecular-weight ones, possibly attributable to the different binding routes/modes of these two groups of PAHs to the particles during combustion. Notably, the preferential association of PAHs with colloids is even more pronounced for the subsurface soils, corroborating that the presence of PAHs in the deeper soils is primarily the results of downward migration of PAH-bearing colloids. The findings highlight the important role of colloids as a vector for the subsurface transport of PAHs at e-waste recycling sites, and call for further understanding of colloid-facilitated transport of PAHs at e-waste recycling sites.

Molecular and Structural Characterization of Isomeric Compounds in Atmospheric Organic Aerosol Using Ion Mobility-Mass Spectrometry.

Secondary organic aerosol (SOA) formed through multiphase atmospheric chemistry makes up a large fraction of airborne particles. The chemical composition and molecular structures of SOA constituents vary between different emission sources and aging processes in the atmosphere, which complicates their identification. In this work, we employ drift tube ion mobility spectrometry with quadrupole time-of-flight mass spectrometry (IM-MS) detection for rapid gas-phase separation and multidimensional characterization of isomers in two biogenic SOAs produced from ozonolysis of isomeric monoterpenes, d-limonene (LSOA) and α-pinene (PSOA). SOA samples were ionized using electrospray ionization (ESI) and characterized using IM-MS in both positive and negative ionization modes. The IM-derived collision cross sections in nitrogen gas (DTCCSN2 ) for individual SOA components were obtained using multifield and single-field measurements. A novel application of IM multiplexing/high-resolution demultiplexing methodology was employed to increase sensitivity, improve peak shapes, and augment mobility baseline resolution, which revealed several isomeric structures for the measured ions. For LSOA and PSOA samples, we report significant structural differences of the isomer structures. Molecular structural calculations using density functional theory combined with the theoretical modeling of CCS values provide insights into the structural differences between LSOA and PSOA constituents. The average DTCCSN2 values for monomeric SOA components observed as [M + Na]+ ions are 3-6% higher than those of their [M - H]- counterparts. Meanwhile, dimeric and trimeric isomer components in both samples showed an inverse trend with the relevant values of [M - H]- ions being 3-7% higher than their [M + Na]+ counterparts, respectively. The results indicate that the structures of Na+-coordinated oligomeric ions are more compact than those of the corresponding deprotonated species. The coordination with Na+ occurs on the oxygen atoms of the carbonyl groups leading to a compact configuration. Meanwhile, deprotonated molecules have higher DTCCSN2 values due to their elongated structures in the gas phase. Therefore, DTCCSN2 values of isomers in SOA mixtures depend strongly on the mode of ionization in ESI. Additionally, PSOA monomers and dimers exhibit larger DTCCSN2 values (1-4%) than their LSOA counterparts owing to more rigid structures. A cyclobutane ring is present with functional groups pointing in opposite directions in PSOA compounds, as compared to noncyclic flexible LSOA structures, forming more compact ions in the gas phase. Lastly, we investigated the effects of direct photolysis on the chemical transformations of selected individual PSOA components. We use IM-MS to reveal structural changes associated with aerosol aging by photolysis. This study illustrates the detailed molecular and structural descriptors for the detection and annotation of structural isomers in complex SOA mixtures.