Observed Particle Size Distributions Research Articles

Role of Iodine-Assisted Aerosol Particle Formation in Antarctica.

New particle formation via the ion-mediated sulfuric acid and ammonia molecular clustering mechanism remains the most widely observed and experimentally verified pathway. Recent laboratory and molecular level observations indicate iodine-driven nucleation as a potentially important source of new particles, especially in coastal areas. In this study, we assess the role of iodine species in particle formation using the best available molecular thermochemistry data and coupled to a detailed 1-d column model which is run along air mass trajectories over the Southern Ocean and the coast of Antarctica. In the air masses traversing the open ocean, ion-mediated SA-NH3 clustering appears insufficient to explain the observed particle size distribution, wherein the simulated Aitken mode is lacking. Including the iodine-assisted particle formation improves the modeled Aitken mode representation with an increase in the number of freshly formed particles. This implies that more particles survive and grow to Aitken mode sizes via condensation of gaseous precursors and heterogeneous reactions. Under certain meteorological conditions, iodine-assisted particle formation can increase cloud condensation nuclei concentrations by 20%-100%.

Nonequilibrium Behavior in Isoprene Secondary Organic Aerosol.

Recent studies have shown that instantaneous gas-particle equilibrium partitioning assumptions fail to predict SOA formation, even at high relative humidity (∼85%), and photochemical aging seems to be one driving factor. In this study, we probe the minimum aging time scale required to observe nonequilibrium partitioning of semivolatile organic compounds (SVOCs) between the gas and aerosol phase at ∼50% RH. Seed isoprene SOA is generated by photo-oxidation in the presence of effloresced ammonium sulfate seeds at <1 ppbv NOx, aged photochemically or in the dark for 0.3-6 h, and subsequently exposed to fresh isoprene SVOCs. Our results show that the equilibrium partitioning assumption is accurate for fresh isoprene SOA but breaks down after isoprene SOA has been aged for as short as 20 min even in the dark. Modeling results show that a semisolid SOA phase state is necessary to reproduce the observed particle size distribution evolution. The observed nonequilibrium partitioning behavior and inferred semisolid phase state are corroborated by offline mass spectrometric analysis on the bulk aerosol particles showing the formation of organosulfates and oligomers. The unexpected short time scale for the phase transition within isoprene SOA has important implications for the growth of atmospheric ultrafine particles to climate-relevant sizes.

Comprehensive simulations of new particle formation events in Beijing with a cluster dynamics–multicomponent sectional model

Abstract. New particle formation (NPF) and growth are a major source of atmospheric fine particles. In polluted urban environments, NPF events are frequently observed with characteristics distinct from those in clean environments. Here we simulate NPF events in urban Beijing with a discrete-sectional model that couples cluster dynamics and multicomponent particle growth. In the model, new particles are formed by sulfuric acid–dimethylamine nucleation, while particle growth is driven by particle coagulation and the condensation of sulfuric acid, its clusters, and oxygenated organic molecules (OOMs). A variable simulation domain in the particle size space is applied to isolate newly formed particles from preexisting ones, which allows us to focus on new particle formation and growth rather than the evolution of particles of non-NPF origin. The simulation yields a rich set of information including the time-dependent NPF rates, the cluster concentrations, the particle size distributions, and the time- and size-specific particle chemical compositions. These can be compared with the field observations to comprehensively assess the simulation–observation agreement. Sensitivity analysis with the model further quantifies how metrics of NPF events (e.g., particle survival probability) respond to model input variations and serves as a diagnostic tool to pinpoint the key parameter that leads to simulation–observation discrepancies. Seven typical NPF events in urban Beijing were analyzed. We found that with the observed gaseous precursor concentrations and coagulation sink as model inputs, the simulations roughly captured the evolution of the observed particle size distributions; however, the simulated particle growth rate was insufficient to yield the observed particle number concentrations, survival probability, and mode diameter. With the aid of sensitivity analysis, we identified under-detected OOMs as a likely cause for the discrepancy, and the agreement between the simulation and the observation was improved after we modulated particle growth rates in the simulation by adjusting the abundance of OOMs.

Modelling the 2021 East Asia super dust storm using FLEXPART and FLEXDUST and its comparison with reanalyses and observations

The 2021 East Asia sandstorm began from the Eastern Gobi desert steppe in Mongolia on March 14, and later spread to northern China and the Korean Peninsula. It was the biggest sandstorm to hit China in a decade, causing severe air pollution and a significant threat to human health. Capturing and predicting such extreme events is critical for society. The Lagrangian particle dispersion model FLEXPART and the associated dust emission model FLEXDUST have been recently developed and applied to simulate global dust cycles. However, how well the model captures Asian dust storm events remains to be explored. In this study, we applied FLEXPART to simulate the recent 2021 East Asia sandstorm, and evaluated its performance comparing with observation and observation-constrained reanalysis datasets, such as the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and CAMS global atmospheric composition forecasts (CAMS-F). We found that the default setting of FLEXDUST substantially underestimates the strength of dust emission and FLEXPART modelled dust concentration in this storm compared to that in MERRA-2 and CAMS-F. An improvement of the parametrization of bare soil fraction, topographical scaling, threshold friction velocity and vertical dust flux scheme based on Kok et al. (Atmospheric Chemistry and Physics, 2014, 14, 13023–13041) in FLEXDUST can reproduce the strength and spatio-temporal pattern of the dust storm comparable to MERRA-2 and CAMS-F. However, it still underestimates the observed spike of dust concentration during the dust storm event over northern China, and requires further improvement in the future. The improved FLEXDUST and FLEXPART perform better than MERRA-2 and CAMS-F in capturing the observed particle size distribution of dust aerosols, highlighting the importance of using more dust size bins and size-dependent parameterization for dust emission, and dry and wet deposition schemes for modelling the Asian dust cycle and its climatic feedbacks.

An evaluation of biomass burning aerosol mass, extinction, and size distribution in GEOS using observations from CAMP2Ex

Abstract. Biomass burning aerosol impacts aspects of the atmosphere and Earth system through direct and semi-direct effects, as well as influencing air quality. Despite its importance, the representation of biomass burning aerosol is not always accurate in numerical weather prediction and climate models or reanalysis products. Using observations collected as part of the Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) in August through October of 2019, aerosol concentration and optical properties are evaluated within the Goddard Earth Observing System (GEOS) and its underlying aerosol module, GOCART. In the operational configuration, GEOS assimilates aerosol optical depth observations at 550 nm from AERONET and MODIS to constrain aerosol fields. Particularly for biomass burning aerosol, without the assimilation of aerosol optical depth, aerosol extinction is underestimated compared to observations collected in the Philippines region during the CAMP2Ex campaign. The assimilation process adds excessive amounts of carbon to account for the underestimated extinction, resulting in positive biases in the mass of black and organic carbon, especially within the boundary layer, relative to in situ observations from the Langley Aerosol Research Group Experiment. Counteracting this, GEOS is deficient in sulfate and nitrate aerosol just above the boundary layer. Aerosol extinction within GEOS is a function of the mass of different aerosol species, the ambient relative humidity, the assumed spectral optical properties, and particle size distribution per species. The relationship between dry and ambient extinction in GEOS reveals that hygroscopic growth is too high within the model for biomass burning aerosol. An additional concern lies in the assumed particle size distribution for GEOS, which has a single mode radius that is too small for organic carbon. Variability in the observed particle size distribution for biomass burning aerosol within a single flight also illuminates the fact that a single assumed particle size distribution is not sufficient and that for a proper representation, a more advanced aerosol module within GEOS may be necessary.

Dependence of Ice Crystal Size Distributions in High Ice Water Content Conditions on Environmental Conditions: Results from the HAIC-HIWC Cayenne Campaign

Abstract A new method that automatically determines the modality of an observed particle size distribution (PSD) and the representation of each mode as a gamma function was used to characterize data obtained during the High Altitude Ice Crystals and High Ice Water Content (HAIC-HIWC) project based out of Cayenne, French Guiana, in 2015. PSDs measured by a 2D stereo probe and a precipitation imaging probe for particles with maximum dimension (Dmax) &gt; 55 μm were used to show how the gamma parameters varied with environmental conditions, including temperature (T) and convective properties such as cloud type, mesoscale convective system (MCS) age, distance away from the nearest convective peak, and underlying surface characteristics. Four kinds of modality PSDs were observed: unimodal PSDs and three types of multimodal PSDs (Bimodal1 with breakpoints 100 ± 20 μm between modes, Bimodal2 with breakpoints 1000 ± 300 μm, and Trimodal PSDs with two breakpoints). The T and ice water content (IWC) are the most important factors influencing the modality of PSDs, with the frequency of multimodal PSDs increasing with increasing T and IWC. An ellipsoid of equally plausible solutions in (No–λ–μ) phase space is defined for each mode of the observed PSDs for different environmental conditions. The percentage overlap between ellipsoids was used to quantify the differences between overlapping ellipsoids for varying conditions. The volumes of the ellipsoid decrease with increasing IWC for most cases, and (No–λ–μ) vary with environmental conditions related to distribution of IWC. HIWC regions are dominated by small irregular ice crystals and columns. The parameters (No–λ–μ) in each mode exhibit mutual dependence.

High-yield microplasma synthesis of monodisperse sub-3 nm diameter metal nanoparticles explained by a charge-mediated formation mechanism

The size and composition of nanoparticles are instrumental to many catalytic processes; for example, their controlled synthesis is key to achieving high yield and quality in aerosol chemical vapor deposition (CVD) of carbon nanotubes (CNTs). Using a custom-built atmospheric pressure DC microplasma reactor, we synthesize sub-3 nm iron nanoparticle aerosols at high number concentration (>109 #/cm3) with narrow size distribution (σg<1.3) from a ferrocene vapor precursor. We demonstrate precise diameter control down to 1.1 nm and maximum yield near unity. We invoke a charge-mediated formation mechanism to show that the ∼ 10 μs plasma residence time is sufficient to dissociate the precursor and partially ionize the resulting iron vapor, yet too short for the aggregation of clusters beyond 10 atoms. Thus, particle growth occurs primarily downstream of the plasma domain through aggregation of neutral and ionized vapor and clusters. This model closely reproduces the observed particle size distributions with the selection of an appropriate fractional ionization, yet is insufficient to entirely explain the rapid growth rate observed experimentally. This mechanism is different from that of existing microplasma processes, which have a longer residence time allowing particle formation to occur within the plasma, and may explain the demonstrated capability to co-optimize nanoparticle yield, throughput, and diameter control at a level exceeding the performance of previously published thermal and microplasma methods.

Stabilitas madu herbal dengan penambahan emulsifier dan antioksidan menggunakan metode spontan

Herbal honey with blackseed oil and olive oil is susceptible to change in stability during the storage period, such as separation and oxidation. The aim of this study was to observe the effect of emulsifier and antioxidant to stability of herbal honey. This study used a completely randomized factorial design with two repetitions. The first factor was concentration antioxidant tocopherol (0; 0,005; 0,01%) and the second factor was concentration of emulsifier Tween 80 (0; 0,001; 0,002%) so there were 9 combinations. Herbal honey was made using the spontaneous method. The study observed particle size distribution, stability against separation, and predict shelf life. Based on observation, the largest particle size distribution was in the herbal honey T1TW1 group with size 1004.70 ± 5.80 nm. The smallest particle distribution was in the T3TW3 group with size 117.10 ± 1.56 nm. Based on the stability, T3TW3 group was able to keep the rate of emulsion separation that occurs compared to other groups. Based on ASLT test, herbal honey with antioxidan and emulsifier had shelf life 241 days and without 140 days. Conclusion this study is antioxidant tocopherol and Tween 80 emulsifier can improve the stability of herbal honey significant.

The Precipitation Imaging Package: Assessment of Microphysical and Bulk Characteristics of Snow

Remote-sensing observations are needed to estimate the regional and global impacts of snow. However, to retrieve accurate estimates of snow mass and rate, these observations require augmentation through additional information and assumptions about hydrometeor properties. The Precipitation Imaging Package (PIP) provides information about precipitation characteristics and can be utilized to improve estimates of snowfall rate and accumulation. Here, the goal is to demonstrate the quality and utility of two higher-order PIP-derived products: liquid water equivalent snow rate and an approximation of volume-weighted density called equivalent density. Accuracy of the PIP snow rate and equivalent density is obtained through intercomparison with established retrieval methods and through evaluation with colocated ground-based observations. The results confirm the ability of the PIP-derived products to quantify properties of snow rate and equivalent density, and demonstrate that the PIP produces physically realistic snow characteristics. When compared to the National Weather Service (NWS) snow field measurements of six-hourly accumulation, the PIP-derived accumulations were biased only +2.48% higher. Additionally, this work illustrates fundamentally different microphysical and bulk features of low and high snow-to-liquid ratio events, through assessment of observed particle size distributions, retrieved mass coefficients, and bulk properties. Importantly, this research establishes the role that PIP observations and higher-order products can serve for constraining microphysical assumptions in ground-based and spaceborne remotely sensed snowfall retrievals.

On Particle Size Distributions in Catalytic Chain Transfer Emulsion Polymerization: Chain-Extension and the Use of Derived Macromonomers as Reactive Surfactants in Emulsion Polymerization.

Catalytic chain transfer emulsion polymerization (CCTP) and subsequent chain extension via reversible addition-fragmentation chain transfer (RAFT) were used to synthesize amphiphilic macromonomers (MM), in the form of polymer latexes. The macromonomers consisted of two blocks whose first was a random copolymer of methacrylic acid and methyl methacrylate, at 35:65 mol:mol, while the second block was n-butyl methacrylate P[(MAA-co-MMA)-block-PBMA]. The block copolymer colloids were disintegrated and micellized upon addition of ammonia. The resulting nanosized polymer dispersions were used as reactive surfactants in the emulsion polymerization of n-butyl methacrylate. For this, a dual stage slow-fast monomer feed profile was used. The final polymer latexes were in the sub-100 nm range for the particle diameter at 30% w/w total polymer content. The emphasis of the work is to discuss and find an explanation for the observed particle size distributions in the three consecutive emulsion polymerization steps. The particle size distribution of the ω-unsaturated macromonomer latex synthesized by CCTP emulsion polymerization was found to be much broader than expected. This discrepancy is attributed to an extended particle nucleation period. The chain extension step in the macromonomer latex preparation showed considerable secondary nucleation. The presence of water-soluble macromonomer species from the CCTP emulsion polymerization step assured that control of chain growth persisted. The use of the amphiphilic macromonomers as reactive surfactants in the form of a nanosized aggregate seed dispersion showed that the average particle diameter could be tuned and that the molecular weight distributions could be regulated, when monomer starved conditions were used in the emulsion polymerizations.

On the Dependence of Cirrus Parametrizations on the Cloud Origin

AbstractParametrizations of Arctic cirrus particle size distributions are presented depending on the cloud origin, either in situ or liquid. The data set used originate from balloon‐borne measurements above Kiruna during winter. The observed particle size distributions are represented by gamma functions. The gamma coefficients exhibit large differences with regard to cloud origin. The functions for Arctic cirrus confirm established parametrizations for continental cirrus sorted by two particle size modes but differ from others depending only on temperature. We suppose that the agreement between the parametrizations of the geographically different cirrus is because in situ and liquid origin cirrus also distinguish by particle size modes. Since cloud sorting by their origin is based on physical processes which are independent of geographical region, we further hypothesize that these cloud‐type‐based parametrizations might be generally valid for use in global models and satellite retrievals, given the distribution of the cloud types is known.

Seasonality of airborne trace element sources in Aracaju, Northeastern, Brazil

In this work the urban area of Aracaju city, located in the State of Sergipe, Northeastern Brazil was the site for simultaneous collection of suspended particles (TSP) and inhalable particulate matter (PM10) aiming an evaluation of the air quality parameters. Concentrations of Cd, Co, Cu, Fe, Mn, Ni, Pb and V in TSP and PM10 were determined by inductively coupled plasma mass spectrometry (ICP-MS). Iron was the most abundant element found in both particulate samples. Through chemometric tools, it was possible to point out that the contributions to the TSP and PM10 formation are similar, and strong correlations were observed between Fe-Mn (0.83) and Cd-Pb (0.93) in TSP, and Fe-Mn (0.90), Fe-Cu (0.81) and Cd-Pb (0.97) in PM10, an evidence that these species are from sources related mainly to soil resuspension and vehicular traffic. Enrichment factor (EF) and geoaccumulation index (Igeo) showed an influence of fossil fuel burning in the composition of TSP and PM10. Through principal component analysis (PCA) and hierarchical cluster analysis (HCA) it was observed particle size distribution groupings according to its aerodynamic size. Evaluation of the concentrations obtained for the collected samples according to the seasons (dry and rainy), indicated the influence of both, biogenic (resuspension of soil and marine aerosols) and anthropic (vehicle traffic and biomass burning) sources.

The effect of fragmentation on the distribution of hillslope rock size and abundance: Insights from contrasting field and model data

The disintegration of rocks into soil plays an important role in geomorphological processes, such as the evolution of hillslopes and river valleys. Nevertheless, the factors and processes controlling the physical weathering of rock particles are poorly understood. In this study, the surface and subsurface distribution of rock fragments abundance and size is measured in ten soil profiles along three hillslopes transects. For the surface horizons, we observed a significant linear relation between the ninth decile of the diameter, d90, and hillslope gradient and for both surface and subsurface horizons, a significant logarithmic relation between d90 and rock fragment abundance. For the first time, the performance of various fragmentation models is compared against field data to evaluate if the surface rock distribution can be explained from fragmentation of the subsurface material only. In six profiles these fragmentation models adequately reproduced the observed particle size distribution. In the other four profiles, all located on eroding hillslopes, armouring dominates over fragmentation and the surface rock distribution is coarser compared to the subsurface. Generally, the profiles have a good fit to almost all models with the exception of two. However, we can differentiate two zones in terms of fragmentation mechanism according to the modelling results. The profiles in the transect located along a gently sloping hillslope, and the two other profiles, along a steep river valley.In the models, we consider physical weathering as the single factor of particle size evolution, except or two models where conceptual chemical weathering of the fine fraction is considered, although this chemical weathering was not specifically designed to explore soil water chemistry or mineralogy in detail. The observed discrepancies between field data and the results of this study, especially in the fine fraction, reveal the possible relevance of chemical or biological weathering, redistribution processes and the lower accuracy of the number of fine fraction classes established and measured than in the coarse fraction for the field data.

Airborne validation of radiative transfer modelling of ice clouds at millimetre and sub-millimetre wavelengths

Abstract. The next generation of European polar orbiting weather satellites will carry a novel instrument, the Ice Cloud Imager (ICI), which uses passive observations between 183 and 664 GHz to make daily global observations of cloud ice. Successful use of these observations requires accurate modelling of cloud ice scattering, and this study uses airborne observations from two flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 research aircraft to validate radiative transfer simulations of cirrus clouds at frequencies between 325 and 664 GHz using the Atmospheric Radiative Transfer Simulator (ARTS) and a state-of-the-art database of cloud ice optical properties. Particular care is taken to ensure that the inputs to the radiative transfer model are representative of the true atmospheric state by combining both remote-sensing and in situ observations of the same clouds to create realistic vertical profiles of cloud properties that are consistent with both observed particle size distributions and bulk ice mass. The simulations are compared to measurements from the International Submillimetre Airborne Radiometer (ISMAR), which is an airborne demonstrator for ICI. It is shown that whilst they are generally able to reproduce the observed cloud signals, for a given ice water path (IWP) there is considerable sensitivity to the cloud microphysics, including the distribution of ice mass within the cloud and the ice particle habit. Accurate retrievals from ICI will therefore require realistic representations of cloud microphysical properties.

Nonparametric Methodology to Estimate Precipitating Ice from Multiple-Frequency Radar Reflectivity Observations

AbstractIn this study, a nonparametric method to estimate precipitating ice from multiple-frequency radar observations is investigated. The method does not require any assumptions regarding the distribution of ice particle sizes and relies on an efficient search procedure to incorporate information from observed particle size distributions (PSDs) in the estimation process. Similar to other approaches rooted in optimal-estimation theory, the nonparametric method is robust in the presence of noise in observations and uncertainties in the forward models. Over 200 000 PSDs derived from in situ observations collected during the Olympic Mountains Experiment (OLYMPEX) and Integrated Precipitation and Hydrology Experiment (IPHEX) field campaigns are used in the development and evaluation of the nonparametric estimation method. These PSDs are used to create a database of ice-related variables and associated computed radar reflectivity factors at the Ku, Ka, and W bands. The computed reflectivity factors are used to derive precipitating ice estimates and investigate the associated errors and uncertainties. The method is applied to triple-frequency radar observations collected during OLYMPEX and IPHEX. Direct comparisons of estimated ice variables with estimates from in situ instruments show results consistent with the error analysis. Global application of the method requires an extension of the supporting PSD database, which can be achieved through the processing of information from additional past and future field campaigns.

In vivo-induced size transformation of cerium oxide nanoparticles in both lung and liver does not affect long-term hepatic accumulation following pulmonary exposure.

Recent findings show that cerium oxide (CeO2) nanoparticles may undergo in vivo-induced size transformation with the formation of smaller particles that could result in a higher translocation following pulmonary exposure compared to virtually insoluble particles, like titanium dioxide (TiO2). Therefore, we compared liver deposition of CeO2 and TiO2 nanoparticles of similar primary sizes 1, 28 or 180 days after intratracheal instillation of 162 μg of NPs in female C57BL/6 mice. Mice exposed to 162 μg CeO2 or TiO2 nanoparticles by intravenous injection or oral gavage were included as reference groups to assess the amount of NPs that reach the liver bypassing the lungs and the translocation of NPs from the gastrointestinal tract to the liver, respectively. Pulmonary deposited CeO2 nanoparticles were detected in the liver 28 and 180 days post-exposure and TiO2 nanoparticles 180 days post-exposure as determined by darkfield imaging and by the quantification of Ce and Ti mass concentration by inductively coupled plasma-mass spectrometry (ICP-MS). Ce and Ti concentrations increased over time and 180 days post-exposure the translocation to the liver was 2.87 ± 3.37% and 1.24 ± 1.98% of the initial pulmonary dose, respectively. Single particle ICP-MS showed that the size of CeO2 nanoparticles in both lung and liver tissue decreased over time. No nanoparticles were detected in the liver following oral gavage. Our results suggest that pulmonary deposited CeO2 and TiO2 nanoparticles translocate to the liver with similar calculated translocation rates despite their different chemical composition and shape. The observed particle size distributions of CeO2 nanoparticles indicate in vivo processing over time both in lung and liver. The fact that no particles were detected in the liver following oral exposure showed that direct translocation of nanoparticles from lung to the systemic circulation was the most important route of translocation for pulmonary deposited particles.

In Situ Microphysical Observations of the 29–30 May 2012 Kingfisher, OK, Supercell With a Balloon‐Borne Video Disdrometer

AbstractThe microphysical characteristics of deep convective storms are a critically important, yet difficult aspect of storm morphology to observe in situ. These observations play a large role in several areas of ongoing research, but detailed observations in key portions of clouds do not exist with the currently available measurement platforms. To facilitate these observations, a balloon‐borne particle imaging device known as the PArticle Size, Image, and Velocity (PASIV) probe was developed at the National Severe Storms Laboratory, which is capable of measuring particle counts on scales as small as 50 m. The videosonde observations from the PASIV showed that precipitation particle counts change rapidly between analysis layers, sometimes by as much as a few orders of magnitude (102–104 in adjacent layers), and radar reflectivities calculated directly from observed particle size distributions agree with mobile radar measurements. Furthermore, the observations allow the distributions to be partitioned into various particle types, which sheds light on which particles are dominating the radar signal at various times. These distributions per particle type, and their associated mixing ratios, agree with independent model analysis. Additionally, single‐, double‐, and triple‐moment parameterized particle size distribution functions are fit to various layers, with the general result that ice particles are easily represented by exponential distributions while rain is better fit with a gamma distribution. The parametric fits for ice and rain distributions found here support previous work and some portions of modeled microphysics, but also suggest room for improvement when deciding which schemes to use with cloud modeling.

Investigation of nucleation kinetics in H2SO4 vapor through modeling of gas phase kinetics coupled with particle dynamics.

We have developed a new model utilizing our existing kinetic gas phase models to simulate experimental particle size distributions emerging in dry supersaturated H2SO4 vapor homogeneously produced by rapid oxidation of SO2 through stabilized Criegee-Intermediates from 2-butene ozonolysis. We use a sectional method for simulating the particle dynamics. The particle treatment in the model is based on first principles and takes into account the transition from the kinetic to the diffusion-limited regime. It captures the temporal evolution of size distributions at the end of the ozonolysis experiment well, noting a slight underrepresentation of coagulation effects for larger particle sizes. The model correctly predicts the shape and the modes of the experimentally observed particle size distributions. The predicted modes show an extremely high sensitivity to the H2SO4 evaporation rates of the initially formed H2SO4 clusters (dimer to pentamer), which were arbitrarily restricted to decrease exponentially with increasing cluster size. In future, the analysis presented in this work can be extended to allow a direct validation of quantum chemically predicted stabilities of small H2SO4 clusters, which are believed to initiate a significant fraction of atmospheric new particle formation events. We discuss the prospects and possible limitations of the here presented approach.

Particle size distributions of lead measured in battery manufacturing and secondary smelter facilities and implications in setting workplace lead exposure limits

ABSTRACTInhalation plays an important role in exposures to lead in airborne particulate matter in occupational settings, and particle size determines where and how much of airborne lead is deposited in the respiratory tract and how much is subsequently absorbed into the body. Although some occupational airborne lead particle size data have been published, limited information is available reflecting current workplace conditions in the U.S. To address this data gap, the Battery Council International (BCI) conducted workplace monitoring studies at nine lead acid battery manufacturing facilities (BMFs) and five secondary smelter facilities (SSFs) across the U.S. This article presents the results of the BCI studies focusing on the particle size distributions calculated from Personal Marple Impactor sampling data and particle deposition estimates in each of the three major respiratory tract regions derived using the Multiple-Path Particle Dosimetry model. The BCI data showed the presence of predominantly larger-sized particles in the work environments evaluated, with average mass median aerodynamic diameters (MMADs) ranging from 21–32 µm for the three BMF job categories and from 15–25 µm for the five SSF job categories tested. The BCI data also indicated that the percentage of lead mass measured at the sampled facilities in the submicron range (i.e., <1 µm, a particle size range associated with enhanced absorption of associated lead) was generally small. The estimated average percentages of lead mass in the submicron range for the tested job categories ranged from 0.8–3.3% at the BMFs and from 0.44–6.1% at the SSFs. Variability was observed in the particle size distributions across job categories and facilities, and sensitivity analyses were conducted to explore this variability. The BCI results were compared with results reported in the scientific literature. Screening-level analyses were also conducted to explore the overall degree of lead absorption potentially associated with the observed particle size distributions and to identify key issues associated with applying such data to set occupational exposure limits for lead.

DEM simulation of polyhedral particle cracking using a combined Mohr–Coulomb–Weibull failure criterion

In this work, at first a new failure criterion for breakage of brittle particle systems is proposed, which combines the classical Mohr–Coulomb strength criterion with the probabilistic Weibull concept. This failure criterion is especially applicable to particle systems under compression load and accounts for the size-dependence of the material’s strength. Second, the Discrete Element Method (DEM) is implemented for sharp edged particles of convex polyhedral shape. The Mohr–Coulomb–Weibull criterion is integrated into the running DEM procedure to simulate progressive particle cracking and comminution of particle systems. The feasibility of the model was tested with simple uniaxial and triaxial compressive loading states, and the influence of relevant material parameters was studied. As a first application example of the method, an oedometric experiment was simulated, whereby coarse quartzite particles are compressed in a piston-die press. The results show good qualitative agreement with the experimentally observed particle size distribution. Thus, the ability of the suggested approach has been proved to reproduce important features as the size effect and the influence of stress state.