Size Distribution Of Dust Particles Research Articles

Study on the dust production characteristics of coal cutting at different drilling speeds of cutting head

In order to address the unclear mechanism of dust generation during coal cutting by picks at the current driving face, experiments on dust generation at different drilling speeds were conducted using a self-built experimental apparatus for coal cutting dust. Numerical simulations were also employed to further analyze the dust generation mechanism during coal cutting by cutter picks. The research findings indicate that as the drilling speed increases, the dust generation initially increases and then stabilizes. The peak values of total dust and potentially respirable dust generation rates were observed at a drilling speed of 200mm/min, reaching 204.21g/t and 29.73g/t, respectively. The particle size distribution of dust generated from the cutting of the same coal followed a similar trend. The coal fragmentation by cutter picks is a result of the combined action of tensile and shear forces. The growth of crack quantity follows an S-shaped curve, characterized by slow growth, rapid growth, and stabilization. With an increase in cutting depth, both the force and torque on the cutting head exhibited a continuous increase followed by stable fluctuations. The energy consumption during the cutting process mainly involves overcoming the coal's strain energy, and the trend of energy dissipation initially increases and then decreases. These research findings provide a theoretical basis for further understanding the mechanism of coal cutting dust generation by cutter picks and achieving efficient control of dust emissions at the source.

Hazard and pollution characteristics of rock-containing dust in coal mine tunneling faces based on experimental and numerical study

The rock-containing dust poses a serious threat to the safe and efficient operation of coal mine tunneling faces (CMTFs). This study investigates the hazard and pollution characteristics of rock-containing dust in CMTFs by testing wettability, lithology surface functional groups, and particle size distribution of dusts with varying rock content. Furthermore, the spatial and temporal evolution of rock-containing dusts is explored through CFD simulation and the effects of rock-containing dust on the dedusting characteristics of water spray are analyzed. The results show that the crystallinity exhibits an exponential growth trend as the mudstone content increases, and the respirable dusts < 2.5μm and < 7μm increase by 15.04 % and 24.28 %, respectively. The rock-containing dust reaches the end of the simulated tunnel in just 50 seconds. On both the driver’s and pedestrian’s sides, the dust concentration shows an approximate S-shaped increase over time. Under the condition that only traditional water spraying measures are implemented, the concentration of respirable rock-containing dust will be approximately 1.2–1.5 times higher than the concentration of respirable coal dust. The results have provided valuable insights into the hazard and pollution characteristics of rock-containing dust in CMTFs, which are crucial for guiding dust disaster management in coal mines.

Impact of anthropogenic and natural constituents on particulate matter in oasis cities on the southern margin of the Taklimakan Desert based on MERRA-2 and multi-site ground observation

Dust storms are associated with large amounts of particulate matter (PM) that can have adverse effects on health and the environment. The contribution of natural dust to atmospheric PM levels represents a scientific challenge, especially in areas with close proximity to dust sources. To improve our knowledge in this area, we collected 300 PM filter-samples across five oasis cities on the southern edge of the Taklimakan Desert in 2016, and applied the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) data to quantify the contribution of natural dust to PM on sand dust and non-sand dust days. Research has shown that the particle size distribution of mineral dust in Taklimakan dust aerosols was relatively uniform. On sand dust days, CaSO4 and Na2SO4 were directly emitted from the surface, leading to higher sulfate concentrations in PM. While the increase in the proportions of organic carbon - OC1 and OC2 was attributed to the mixed anthropogenic emissions. On non-sand dust days, SO42− concentration was significantly affected by emissions from anthropogenic sources. The automotive composite emissions and coal combustion were the main sources of elemental carbon - EC1. Based on the results of MERRA-2 reanalysis data, natural dust constituted 53 % and 70 % of the total PM2.5 and PM10, respectively. In this study, we have quantified the contribution of natural dust under different weather conditions and identifying potential sources of PM in oasis cities. This study provides support for the assessment of natural dust and PM prevention in oasis cities.

Research on particle size distribution and composition of road deposit dust in Xi'an: From the perspective of non-exhaust emissions

Road dust, containing tire-road wear particles, atmospheric dust, or construction-related particles, contaminates road environments and poses a health hazard when inhaled by humans. To further explore the particle size and composition of road deposit dust, this study collects these particles in Xi'an, considering various road grades, materials, service conditions, sections, and locations. The collected particles undergo electron microscopy, laser particle size, thermal, mass spectrometry, infrared spectroscopy, and inductively coupled plasma analyses. Qualitative and quantitative analysis of the particles has been conducted, leading to the following conclusions: Asphalt & tire contribute 8.5% of the road deposit dust, while wear from calcium carbonate accounts for approximately 30%. The average particle size on urban roads (392 μm) is 1.25 times that of rural roads (312 μm). The smaller particles on rural roads are more easily resuspended and inhaled, posing health risks and requiring more attention. Brake zones, which often have 1.4 times the metal content compared to mid-sections, including potentially carcinogenic chromium (Cr), should receive focused watering and adsorption due to brake zone where is also at intersections and pedestrian crossing. New roads, which generate 3-6 times more organic matter than old roads, requires continuous cleaning after opening to traffic. Surface-blocked asphalt concrete (AC) pavements, as their lack of pores can lead to easy re-suspension of deposited particles due to tire-road interaction should also be attention. This study aims to contribute to the field of traffic-related dust pollution cleaning strategies and non-exhaust emissions mitigation measures in the future.

Spectral ratioing of [formula omitted] to constrain the dust particle size distribution of comets

A numerical model of cometary dust environments is used to gain a deeper understanding of the relationship between the brightness (Afρ) and the dust particle size distribution in the coma. Specifically, the spectral ratio of Afρ(425 nm)/Afρ(900 nm) is modelled for a wide range of parameters and tied to the power-law index. The studied parameters are dust composition, terminal outflow velocity and the dust production rate day–night asymmetry. We find that the spectral ratio of Afρ modelled at 425 nm and 900 nm correlates with the power-law index of the particle size distribution. This method could be used to place constraints on the dust size distributions of comets and as a result improve the use of Afρ as a proxy for cometary activity. Optically red dust indicates that the scattering is dominated by large particles.

Assessment of atmospheric air pollution in Dnipro city as a result of dust entrainment from the ash-disposal areasof Prydniprovsk TPP

Purpose. The purpose of this work is to assess the pollution of atmospheric air in Dnipro city as a result of dust entrainment from the ash-disposal areas of Prydniprovsk TPP. The methods. Assessment of atmospheric air pollution in the city of Dnipro as a result of dust entrainment from the ash-disposal areas of Prydniprovska TPP was carried out as follows: physical and chemical characteristics of the stored fly ash were determined; specific dust entrainment from the surface of dry beaches of ash-disposal areas under the most favorable conditions was determined; mathematical modeling of the spread of atmospheric air pollution of Dnipro city by suspended particles was carried out using UPCAP "ECO Center"program; a comparative assessment of dust entrainment reduction due to the gradual processing of the deposited fly ash was carried out. Findings. Almost 100% of the total mass of ash consists of particles smaller than 80 μm, the content of particles smaller than 10 and 2.5 μm is 27.7 and 8.2%, respectively. The main chemical compounds contained in ash are silicon dioxide, aluminum oxide, iron (III) oxide and carbon. The gross entrainment of substances in the form of suspended fine-grained solid particles from the surface of the dry beaches of the Prydniprovska TPP ash-disposal facilities is 18,654 tons per year. The area of atmospheric air pollution of Dnipro city by suspended particles is about 850 km2 and covers Samarskyi, Sobornyi, partly Industrialnyi and Shevchenkivskyi Districts. As a result of the implementation of a waste-free technology for the processing of fly ash with the utilization of the iron-containing fraction, the area of pollution can be reduced by 13.5 times up to 63 km2, the contamination zone in this case will cover underpopulated part of Samarskyi District of the city of Dnipro. Scientific novelty. A refined dependence of the particle size distribution of the mature Prydniprovsk TPP fly ash particles was determined for the further assessment of potential dust entrainment. For the first time, modeling of the distribution of fine-grained particles of fly ash of the Prydniprovsk TPP in the atmospheric air of the city of Dnipro was carried out, taking into account meteorological conditions, conditions of dust formation and particle size distribution. Practical implementation. The results of the research can contribute to reducing the level of atmospheric air pollution in the city of Dnipro. This will improve the quality of life of the local population and protect the natural environment from negative impacts. Research results can also be a basis for the development and implementation of technological solutions for the waste-free processing of stored fly ash with marketable products obtaining.

Larger Dust Cooling Effect Estimated From Regionally Dependent Refractive Indices

AbstractThe dust direct radiative effect (DRE) depends strongly on the dust particle size distribution (PSD) and complex refractive index (CRI). Although recent studies constrained the dust PSD in the models, its CRI uncertainties are still large. As a result, whether dust warms or cools the climate system remains unclear. Here, we estimate the dust DRE by employing the regionally‐dependent dust CRI based on global measurements. We find that new dust CRI significantly enhances the scattering of dust in the shortwave while reduces its absorption in the longwave, which is opposite to that caused by increasing the coarse and giant dust fraction via constraining the PSD. Constraining both PSD and CRI ultimately leads to a net dust DRE of −0.68 W m−2, a cooling stronger than current model estimates.

Analyzing dust particle size and size distribution on extracted particles by SEM and comparing with light scattering techniques

AbstractThis study investigates the measurement of plasma‐grown nanoparticles, comparing ex situ scanning electron microscopy (SEM) and an in situ light scattering method which is based on Mie theory and utilizes a neural network for evaluation. The research reveals that the particle size distribution (PSD) is normal and very narrow, supporting the common assumption of monodisperse particle clouds. Importantly, the study finds that the spread of the PSD increases proportionally with the mean size, suggesting varied growth rates based on the radius of the spherical dust grains. Both methods produce consistent results, which encourages the use of the interference‐free, real‐time, light‐based Mie method in similar studies.

Effects of dust controls on respirable coal mine dust composition and particle sizes: case studies on auxiliary scrubbers and canopy air curtain

Control of dust in underground coal mines is critical for mitigating both safety and health hazards. For decades, the National Institute of Occupational Safety and Health (NIOSH) has led research to evaluate the effectiveness of various dust control technologies in coal mines. Recent studies have included the evaluation of auxiliary scrubbers to reduce respirable dust downstream of active mining and the use of canopy air curtains (CACs) to reduce respirable dust in key operator positions. While detailed dust characterization was not a focus of such studies, this is a growing area of interest. Using preserved filter samples from three previous NIOSH studies, the current work aims to explore the effect of two different scrubbers (one wet and one dry) and a roof bolter CAC on respirable dust composition and particle size distribution. For this, the preserved filter samples were analyzed by thermogravimetric analysis and/or scanning electron microscopy with energy dispersive X-ray. Results indicate that dust composition was not appreciably affected by either scrubber or the CAC. However, the wet scrubber and CAC appeared to decrease the overall particle size distribution. Such an effect of the dry scrubber was not consistently observed, but this is probably related to the particular sampling location downstream of the scrubber which allowed for significant mixing of the scrubber exhaust and other return air. Aside from the insights gained with respect to the three specific dust control case studies revisited here, this work demonstrates the value of preserved dust samples for follow-up investigation more broadly.

Research and Industrial Test of Anti-Freezing and Dust Suppression Agent for Truck Roads in Open-Pit Mines in Inner Mongolia, China

To effectively resolve the inherent conflict between dust control and ice prevention on truck roads during North Surface Coal Mine winters, initially, via monomer preference experiments, the optimal monomers for wetting, moisturizing, and condensing functions were identified as sodium dodecylbenzene sulfonate (B), glycerol (N), and polyacrylamide (R). In parallel, through compound synergistic experiments, the constituent elements of an anti-freezing agent were determined, referred to as F. Subsequently, a four-factor three-level orthogonal test was conducted employing the monomers B, N, R, and the anti-freezing agent F. This evaluation focused on four principal control parameters: penetration rate, evaporation resistance, viscosity, and freezing point. The results led to the identification of the optimal antifreeze and dust suppressant formulation, designated as B2N3R1F3. Within the North Open-Pit Coal Mine, the self-developed dust suppressant was applied to the field test section. Multiple parameters were examined for 6 consecutive days, encompassing the water content of the pavement geotechnical soil, the concentrations of total dust and exhaled dust, and the particle size distribution of dust within this road section. The field test results show that: the average water content of the road surface within the dust suppressant test section measured at 12%; the dust reduction efficiency of total dust and exhaled dust is 93% and 91%; the proportion of dust particles with a size exceeding 500 μm increased by 54.6%. These comprehensive findings provide a empirical framework for the effective resolution of the practical challenge of simultaneously managing dust control and frost protection on truck roads within surface coal mines.

Influence mechanism of dispersion and agglomeration characteristics of micron/nano carbon dust on its combustion kinetics and explosion process

Due to the widespread use of lithium-ion batteries, evaluations of the flammability and explosive characteristics of carbon dust materials as anodes require attention. Carbon dust often reaches the micron/nano scale, and dust particle state and explosion risk generated in different industrial scenarios are different, which is in urgent need of research. Nanoscale dust has relatively static coagulation properties and shows characteristics of dispersion and reagglomeration under a certain airflow. The particle size characteristics affect its thermodynamic characteristics and various consequence parameters of dust explosion. The oxidation and combustion characteristics are mainly affected by dust particle size distribution characteristics. The apparent activation energy is mainly affected by the proportion of small and medium-sized particles and pre-exponential index factor is mainly affected by the dust overall average particle size and specific surface area. The explosion consequence parameters are affected by the thermodynamic parameters, by the disturbance state, particle distribution degree of dust cloud and other factors, which affect the heat radiation and heat transfer process to some extent resulting in different explosion consequence parameters. Due to the agglomeration characteristics of nano-level dust, the minimum ignition energy and minimum ignition temperature of nano-level dust are generally smaller than that of micron level dust.

Rapid characterization of combustible particle breakage via dry dispersion laser diffraction

Dust explosion hazards can be analyzed by various explosion parameters, which are known to depend on the particle size distribution of combustible dust. Literature has evidenced the dispersion system in laboratory apparatus (e.g., 20-L chamber) breaks the original dust into smaller sizes. Such unexpected particle breakage can lead to misleading explosion results which may exaggerate the actual hazards. This study develops a novel solution to identify combustible particle breakage by exploiting dry dispersion laser diffraction technology. Nine samples were dispersed under different levels of energy in a particle size analyzer. Serious particle breakage is confirmed if the tested particle size decreases significantly with increasing dispersion pressure. Eight particle size parameters were plotted to derive quantitative pressure titration curves. A larger average slope in percentage decreases of D10, D50, and D3,2 represents a higher particle breakage tendency. The characterization results are well correlated to previous breakage classification in the 20-L chamber.

Polysaccharide Composite Films Utilising Wood Waste.

This study aimed to investigate the effect of raw waste pine wood dust (Pinus sylvestris) from furniture production on polysaccharide biopolymer film properties. The obtained biocomposite films produced via the casting method were prepared with 20% glycerol and 0%, 5%, 10%, 15%, 20%, and 25% of added wood dust in relation to the dry starch matter. Wood dust composition and particle size distribution analysis were performed. In order to evaluate the material surface properties, tests were carried out using an atomic force microscope (AFM) and a contact angle goniometer. Utilising uniaxial tensile test methodology, the values for both tensile strength and Young's modulus were determined. In addition, the barrier properties, water solubility index, and colour were also investigated. The research showed that wood dust affected the functional parameters of the obtained biocomposites. A wood dust content increase causes the Young's modulus value to rise with a progressive decrease in the max. strain. The filler did not change the films' wetting properties, and each had a hydrophilic surface regardless of the additive amount. The bio-sourced composites obtained were non-toxic and environmentally neutral materials, suitable to be applied in the packaging industry as well as the agriculture sector.

Design and comparison of a suitable dust separation technique during the machining process in a CNC machining center

Design and comparison of a suitable separation technique during the machining process in a CNC machining center. The paper deals with the issue of chip extraction from the milling process in a CNC machining center. The paper aimed to compare the particle size distribution of dust generated in the milling process of natural wood (beech, oak, and spruce) and MDF on a 5-axis CNC machining center. The particle size distribution was evaluated using sieve analysis of samples from the total weight of the captured dust. The results showed that the processing of natural wood is mainly characterized by the formation of coarse dust fractions (2 mm - 1 mm sieves), while the processing of MDF was associated with the formation of fine dust fractions with a size below 100 μm. Another of the objectives was to compare the separation values on the fractional separation curves of selected mechanical separators and filters with the size distribution of dust particles and to propose a suitable separation technique that meets the criteria of "best available technique" (BAT) in the processing of natural wood and MDF, as well as to point out the creation of and the production of harmful dust fractions, which arise mainly during the processing of MDF. We intended to assess whether the introduction of the given technology with the given material mix will also require modifications on the side of the extraction device.

Insights into the size-resolved dust emission from field measurements in the Moroccan Sahara

Abstract. The particle size distribution (PSD) of mineral dust has a strong effect on the impacts of dust on climate. However, our understanding of the emitted dust PSD, including its variability and the fraction of super-coarse dust (diameter &gt;10 µm), remains limited. Here, we provide new insights into the size-resolved dust emission process based on a field campaign performed in the Moroccan Sahara in September 2019 in the context of the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) project. The obtained dust concentration and diffusive flux PSDs show significant dependencies upon the friction velocity (u*), wind direction and type of event (regular events versus haboob events). For instance, the number fraction of sub-micrometre particles increases with u*, along with a large decrease in the mass fraction of super-coarse dust. We identify dry deposition, which is modulated by u* and fetch length, as a potential cause for this PSD variability. Using a resistance model constrained with field observations to estimate the dry deposition flux and thereby also the emitted dust flux, we show that deposition could represent up to ∼90 % of the emission of super-coarse particles (&gt;10 µm) and up to ∼65 % of the emission of particles as small as ∼5 µm in diameter. Importantly, removing the deposition component significantly reduces the variability with u* in the PSD of the emitted dust flux compared with the diffusive flux, particularly for super-coarse dust. The differences between regular and haboob event concentration and diffusive flux PSDs are suspected to result from a smaller and variable dust source fetch during the haboob events, and/or an increased resistance of soil aggregates to fragmentation associated with the observed increase in relative humidity along the haboob outflow. Finally, compared to the invariant emitted dust flux PSD estimated based on brittle fragmentation theory, we obtain a substantially higher proportion of super-micrometre particles in the dust flux. Overall, our results suggest that dry deposition needs to be adequately considered to estimate the emitted PSD, even in studies limited to the fine and coarse size ranges (&lt;10 µm).

Experimental study of particle deposition on a solar photovoltaic panel based on the response surface method.

To explore the influence of different factors on particle deposition, four crucial factors, including particle size, wind speed, inclination angle, and wind direction angle (WDA), were considered, and the particle deposition concentration was used as the response variable for experimental research. In this paper, the Box‒Behnken design analysis method in the response surface method was used to conduct experiments. First, the element composition, content, morphology characteristics, and particle size distribution of dust particles were analyzed experimentally. The changes in wind speed and WDA were obtained through a month-long test measurement. Then, the effects of particle size (A), wind speed (B), inclination angle (C), and WDA (D) on the deposition concentration were examined utilizing a test rig. The test data were analyzed by using Design-Expert 10 software, and the results show that four factors have different degrees of influence on the particle deposition concentration, in which the inclination angle effect is the smallest. In the two-factor interaction analysis, the P values of AB, AC, and BC are all less than 5%, indicating that the correlation between the two-factor interaction term and the response variable is acceptable. In contrast, the correlation between the single-factor quadratic term and the response variable is weak. According to the analysis results of single-factor and double-factor interactions, the quadratic fitting formula of particle deposition influencing factors and deposition concentration was obtained, which could quickly and accurately calculate the variation trend of particle deposition concentration under different environmental conditions.

Air-Borne Particle Size Distribution of Wood Dust Emitted during Small Scale Forestry Operations

Practices such as tree felling, pruning, logging and chipping wood can produce significant amount of wood particles that can be inhaled by agricultural and forestry workers, triggering an important risk to the health of workers. Especially finest fractions of dust, less than 4 µm in diameter (the respirable fraction) may cause respiratory and dermal diseases, until to the risk of developing nose and sinus adenocancer. The aim of this work was to assess the particle size distribution of wood dust produced during chainsaw operations. In two separate trials (July and December), wood logs of three different species (Eucalyptus sp., Pinus radiata and Quercus cerris) were employed in cutting tests. Two chainsaws, one electric powered by batteries and one endothermic, were employed. To characterize the particle size distribution, samplings were carried out with a dust particle counter placed in the area surrounding the tests’ site. Results showed that the dust was characterized by a major fraction of fine particles around 0.3 µm (72% of the particles from 0.3 to 10 µm). The chainsaw with endothermic engine produced more fine dust of the electric one. Obtained amounts of inhalable wood dust were very variable in values, however attention should be paid to the exposure to wood dust considering potential risks, especially in case of long times of exposure.

Cometary dust collected by MIDAS on board Rosetta

Context. The Micro-Imaging Dust Analysis System (MIDAS) atomic force microscope (AFM) on board the Rosetta comet orbiter has been dedicated to the collection and 3D topographical investigation of cometary dust in the size range of a few hundreds of nanometers to tens of micrometers with a resolution down to a few nanometers. Aims. We aim to catalog all dust particles collected and analyzed by MIDAS, together with their main statistical properties such as size, height, basic shape descriptors, and collection time. Furthermore, we aim to present the scientific results that can be extracted from the catalog, such as the size distribution and statistical characteristics of cometary dust particles. Methods. Through a careful re-analysis of MIDAS AFM images, we make a significant update and improvement to the existing MIDAS particle catalog, resulting in the addition of more particles and newly developed shape descriptors. The final product is a comprehensive list of all possible cometary dust particles detected by MIDAS. The catalog documents all images of identified dust particles and includes a variety of derived information tabulated one record per particle. Furthermore, the best image of each particle was chosen for subsequent studies. Finally, we created dust coverage maps and clustering maps of the MIDAS collection targets and traced any possible fragmentation of collected particles with a detailed algorithm. Results. The revised MIDAS catalog includes 3523 MIDAS particles in total, where 1857 particles are expected to be usable for further analysis (418 scans of particles before perihelion + 1439 scans of particles after perihelion, both after the removal of duplicates), ranging from about 40 nm to about 8 μm in size. The mean value of the equivalent radius derived from the 2D projection of the particles is 0.91 ± 0.79 μm. A slightly improved equivalent radius based on the particle’s volume coincides in the range of uncertainties with a value of 0.56 ± 0.45 μm. We note that those sizes and all following MIDAS particle size distributions are expected to be influenced by the fragmentation of MIDAS particles upon impact on the collection targets. Furthermore, fitting the slope of the MIDAS particle size distribution with a power law of a · rb yields an index b of ~−1.67 to −1.88. Lastly, based on the created dust coverage maps and clustering maps of the MIDAS collection targets, we determined the particle fragmentation ratio of 4.09 for nominal activity and 11.8 for the outburst, which underlines that parent particles with faster impact velocity are more likely to be fragmented during dust collection.

Analysis of Size Distribution, Chemical Composition, and Optical Properties of Mineral Dust Particles from Dry Deposition Measurement in Tenerife: Determined by Single-Particle Characterization

In this paper, individual particle analysis by automated scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) was used to assess the size-resolved information of composition, size distribution, complex refractive index, and mixing state of mineral dust aerosol particles collected using different passive and active samplers. In the study, over 120,000 particles from 53 samples were analyzed. Results show that dust particles are the dominating mineral particle type during this campaign, comprising different classes of silicates, Si-rich (quartz-like), Ca-rich (calcite-like), CaMg-rich (dolomite-like), and CaS-rich (gypsum-like). The results also show that there is no significant difference in composition between suspended and deposited dust particles. By using the particle composition, the size-resolved complex refractive index of dust particles was calculated. The real part of the refractive index varied between 1.71 and 1.53 for wavelengths in the range of 370 to 950 nm. The imaginary part of the refractive index, determined mostly by iron oxide, varied between 3.28×10−4 and 7.11×10−5 for wavelengths ranging from 250 nm to 1640 nm. In addition, the refractive index values showed a slight decrease with increasing particle size. We also analyzed the potential for buffering of the acid mobilization of iron by other dust compounds. For particles which contain both iron (Fe) and (unprocessed) calcium (Ca), acids that are able to dissolve insoluble Fe particles can react with the Ca particles before reacting with Fe, but eventually, with longer processing time, the Fe particles could be processed. By analyzing the ratio of sulfate mass to the total aerosol mass of individual particles, the mixing state of sulfate particles to the total dust particles was investigated. The analysis showed that the finer dust particles were associated with higher content of sulfate, while the coarse dust particles correspond to lower sulfate contents, revealing that only fine mode sulfate is more internally mixed with mineral dust aerosol particles.

Insights into the single-particle composition, size, mixing state, and aspect ratio of freshly emitted mineral dust from field measurements in the Moroccan Sahara using electron microscopy

Abstract. The chemical and morphological properties of mineral dust aerosols emitted by wind erosion from arid and semi-arid regions influence climate, ocean, and land ecosystems; air quality; and multiple socio-economic sectors. However, there is an incomplete understanding of the emitted dust particle size distribution (PSD) in terms of its constituent minerals that typically result from the fragmentation of soil aggregates during wind erosion. The emitted dust PSD affects the duration of particle transport and thus each mineral's global distribution, along with its specific effect upon climate. This lack of understanding is largely due to the scarcity of relevant in situ measurements in dust sources. To advance our understanding of the physicochemical properties of the emitted dust PSD, we present insights into the elemental composition and morphology of individual dust particles collected during the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) field campaign in the Moroccan Sahara in September 2019. We analyzed more than 300 000 freshly emitted individual particles by performing offline analysis in the laboratory using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDX). Eight major particle-type classes were identified with clay minerals making up the majority of the analyzed particles both by number and mass, followed by quartz, whereas carbonates and feldspar contributed to a lesser extent. We provide an exhaustive analysis of the PSD and potential mixing state of different particle types, focusing largely on iron-rich (Fe oxide-hydroxides) and feldspar particles, which are key to the effects of dust upon radiation and clouds, respectively. Nearly pure or externally mixed Fe oxide-hydroxides are present mostly in diameters smaller than 2 µm, with the highest fraction below 1 µm at about 3.75 % abundance by mass. Fe oxide-hydroxides tend to be increasingly internally mixed with other minerals, especially clays, as particle size increases; i.e., the volume fraction of Fe oxide-hydroxides in aggregates decreases with particle size. Pure (externally mixed) feldspar represented 3.2 % of all the particles by mass, of which we estimated about a 10th to be K-feldspar. The externally mixed total feldspar and K-feldspar abundances are relatively invariant with particle size, in contrast to the increasing abundance of feldspar-like (internally mixed) aggregates with particle size with mass fractions ranging from 5 % to 18 %. We also found that overall the median aspect ratio is rather constant across particle size and mineral groups, although we obtain slightly higher aspect ratios for internally mixed particles. The detailed information on the composition of freshly emitted individual dust particles and quantitative analysis of their mixing state presented here can be used to constrain climate models including mineral species in their representation of the dust cycle.