Composition Of Dust Research Articles

On new methods for measuring and identifying dust microparticles in ambient air

Established health hazards posed by dust microparticles require automated and mobile devices for their assessment. Such devices should provide an opportunity to analyze component and disperse structures of the solid component in ambient air pollution operatively and in real time. In future, they will replace labor-consuming sampling and separate identification of fraction structure and chemical composition of dusts. The aim of this study was to develop and test new methodical, procedural and instrumental approaches to monitoring of solid particles in ambient air. We suggest a hardware and software complex that implements a two-stage scheme for identifying solid particles sampled in ambient air according to the from-coarse-to-fine principle. The first stage involves identifying the total concentration of solid particles by laser diffraction. Microphotographs are taken with iMicro Q2 mini portable microscope with magnification x800. The microscope lens is connected to a camera, which is linked to nVidia Jetson Nano micro PC. The micro PC classifies particles, identifies their contours by using a neural network and deals with image segmentation. The second stage relies on using computer vision that makes it possible to automate routine recognition of particle images created by the microscope in order to calculate levels of different substances in a sample. All the data are analyzed by the second neural network that performs preset calculations in accordance with mathematical logic (model). The network is trained using a library that contains attributed microphotographs of dusts with different qualitative and disperse structures. The algorithm has been tested with some promising results. Identified disperse structures and chemical composition of dusts turn out to be quite similar to those identified by conventional approaches and measurement methods. The method has been shown to offer wide opportunities to identify dust composition and structure, to create dust pollution profiles, and to estimate a contribution made by a specific source to overall pollution. The study results ensure more correct and precise health risk assessment under exposure to dusts in ambient air.

The Power of the Rings: The GRB 221009A Soft X-Ray Emission from Its Dust-scattering Halo

GRB 221009A is the brightest gamma-ray burst (GRB) ever detected that has occurred at low Galactic latitude. Owing to this exceptional combination, its prompt X-ray emission could be detected for weeks in the form of expanding X-ray rings produced by scattering in Galactic dust clouds. We report on the analysis of 20 rings, generated by dust at distances ranging from 0.3 to 18.6 kpc, detected during two X‐ray Multi Mirror (XMM)-Newton observations performed about 2 and 5 days after the GRB. By fitting the spectra of the rings with different models for the dust composition and grain size distribution, we reconstructed the spectrum of the GRB prompt emission in the 0.7–4 keV energy range as an absorbed power law with photon index Γ = 1–1.4 and absorption in the host galaxy N H,z = (4.1–5.3) × 1021 cm−2. Taking into account the systematic uncertainties regarding the column density of dust contained in the clouds producing the rings, the 0.5–5 keV fluence of GRB 221009A can be constrained between 10−3 and 7 × 10−3 erg cm−2. Both the fluence and the photon index indicate the presence of a possible soft excess with respect to the extrapolation of the main GRB peak observed at higher energies.

On the influence of the trace element composition of regoliths on the labor safety of astronauts on the Moon

Introduction. The problem of using near-Earth space to meet various human needs, including the development of minerals, especially on the Moon, is becoming relevant, which increases the importance of research on occupational safety in these conditions. The study aims to research the trace element composition of regoliths in comparison with terrestrial rocks and its significance for the safety of astronauts on the lunar surface. Materials and methods. The researchers evaluated the trace element composition of the regolith by calculating the concentration coefficients and the quality drop coefficient. When identifying homogeneous classes of regoliths by concentrations of 38 chemical elements, we used computer technology to classify multidimensional observations under conditions of self-organization. Results. We know that the concentrations of many trace elements in regoliths significantly exceed their concentrations in terrestrial soils. Calculated for the Luna-16 and Luna-24 marine regoliths, as well as for Apollo-11 and Apollo-12, the quality reduction coefficient varies from 27 to 100, which corresponds to the "crisis" category. This indicates that the content of trace elements in the regolith ranges from weekly critical (27 for the Luna-16 regolith) to highly critical (100 for the Apollo-12 regolith). The researchers identified trace elements whose concentrations in lunar regoliths significantly exceed their concentrations in terrestrial soils: Cr, Be, Co, Sc, Ho, Se, Ni, Au, Ag, Er, Tm, Y, Sm, Gd, Tb, Dy Yb, Lu, Cd, Zr, Sr, Ce, Pr, Nd, Eu. Trace trace elements are included in the group of substances with allergenic, fibrogenic and carcinogenic effects and can have a negative impact on the health of future lunar colonists. Limitations. The authors have conducted the study for the composition of regolith on the surface of the Moon and did not cover aspects of human protection from lunar dust by space stations, structures, spacesuits and special equipment. Conclusion. When assessing the impact of environmental factors on the safety of astronauts during the colonization of the Moon, attention should be paid to the toxicological aspects of working conditions, in particular the trace element composition of regoliths and lunar dust.

A methodology to assess a mobile urban street cleaning activity

An experimental methodology to assess the human exposure of a street cleaning service, performed by a worker handling a leaf blower followed by a water-flushing sweeper, was developed. The sampling campaign was achieved by considering data from road dust, personal air sampling and portable particulate matter detector. The experimental design allowed to obtain qualitative and quantitative information on the chemical composition of road dust, the size and chemical composition of potentially inhalable particles suspended during the street cleaning activity, as well as the duration of the particles' suspension effect. The methodology employed showed: i) the compliance with the occupational exposure threshold values for the total inhalable dust and with the occupational exposure limit values according to national and international regulatory approaches for polycyclic aromatic hydrocarbons (PAH) and inorganic elements; ii) a good agreement of the metals concentrations from the road dust (i.e., calcium, magnesium, potassium, iron, aluminium and sodium) with those from the material collected by the personal air sampler, highlighting the negligible effect of the investigated sweeping activity compared to the material already present on the road; iii) a similar pattern of inorganic elements within the three different monitoring areas; iv) a “dust wave” effect detected by the particle counter lasting no more than 2 min. Thus, such information suggested that performing the urban sweeping activity in the early mornings, when there is a general low PM10-PM2.5 average concentration, low traffic intensity, and the almost absence of passers-by, lead to a low probability of citizens’ exposure.

Characteristics of metal pollution and multi-isotopic signatures for C, Cu, Zn, and Pb in coastal sediments from special management areas in Korea

The concentrations and isotopic compositions of carbon (C), copper (Cu), zinc (Zn), and lead (Pb) in coastal sediments were analyzed to identify potential pollution sources. High concentrations of total organic carbon (TOC) and metals were found close to cities and industrial areas. The isotopic compositions of C, Cu, Zn, and Pb tended to decrease as their concentrations increased. Bi-plots between δ65Cu and δ66Zn showed that the isotopic compositions in most coastal sediments, except sediments around a smelter, were similar to the isotopic compositions of road dust in urban and industrial areas of Korea. Our results suggest that heavy metal pollution in coastal sediments is greatly influenced by the pollution source, such that most metals originate from traffic and industrial activities in the urban environment. This analysis of multiple isotopes provides insights concerning the transport mechanisms and clarifies potential sources of metal contamination in coastal environments.

Fractal Aggregates of Submicron-sized Grains in the Young Planet-forming Disk around IM Lup

Despite rapidly growing disk observations, it remains a mystery what primordial dust aggregates look like and what the physical and chemical properties of their constituent grains (monomers) are in young planet-forming disks. Confrontation of models with observations to answer this mystery has been a notorious task because we have to abandon a commonly used assumption, perfectly spherical grains, and take into account particles with complex morphology. In this Letter, we present the first thorough comparison between near-infrared scattered light of the young planet-forming disk around IM Lup and the light-scattering properties of complex-shaped dust particles. The availability of scattering observations at multiple wavelengths and over a significant range of scattering angles allows for the first determination of the monomer size, fractal dimension, and size of dust aggregates in a planet-forming disk. We show that the observations are best explained by fractal aggregates with a fractal dimension of 1.5 and a characteristic radius larger than ∼2 μm. We also determined the radius of the monomer to be ∼200 nm, and monomers much smaller than this size can be ruled out on the premise that the fractal dimension is less than 2. Furthermore, dust composition comprising amorphous carbon is found to be favorable to simultaneously account for the faint scattered light and the flared disk morphology. Our results support that planet formation begins with fractal coagulation of submicron-sized grains. All the optical properties of complex dust particles computed in this study are publicly available.

Study of air dust content during acceptance of sunflower meal

The article provides information on the dustiness of the air in the working area when accepting sunflower meal at a feed mill, which is carried out by pouring the meal from the bodies of onboard vehicles into the receiving hopper. The results of measurements of dust concentration and assessment of its disperse composition at various stages of acceptance of sunflower meal are presented. The parameters of the disperse composition of dust are of a probabilistic nature, therefore, along with the experimental values, the parameters of the distribution function are given.

Cattle farm dust alters cytokine levels in human airway construct model

Epidemiological studies have revealed some alterations in systemic immunity that associate with farm exposure and the risk of respiratory diseases, but in vitro studies focusing on immunological responses in the airways are scarce. Our aim was to assess how cowshed dust affects the integrity and inflammation of human airway tissue in vitro. Cowshed dust samples were collected from four different dairy farms. Lung tissue constructs were exposed to dust samples in air-liquid interface. Transepithelial resistance of the tissue, secreted proteins, and a panel of pro-inflammatory cytokines, growth factors, and chemokines were analysed. Cowshed dust stimulation was associated mainly with increased production of IL-13, IL-15, IP-10 and IFN-γ. Some differences between farms were seen. Only one farm dust sample induced a significant change in transepithelial resistance, whereas dust from two of the farms induced the secretion of proteins. The exposure to cowshed dust affected protein and cytokine secretion, but the response profiles were not uniform between farms. The effect on tight junction dynamics was less pronounced, suggesting the relevance of soluble factors in induced responses in the airways. Our results indicate that in addition to farm type, the contribution of cowshed characteristics to dust composition and its immunomodulatory properties should be taken into account.

Engineering environmental protection at an industrial facility

The aim of this study is to study engineering safety at an industrial facility. The subject of the study is dangerous and harmful factors of production, which include dust and harmful gases. The objectives of the study is assessing the dispersed composition of dust, which determines the microclimate of the working area on the example of a foundry. The presence of fine dust in the air space of the workshop leads to occupational diseases, such as pneumoconiosis (silicosis), bronchitis, dermatitis, conjunctivitis. The dust dispersion assessment took into account the relationship between the particle size and the speed of movement under the action of gravitational or centrifugal forces. The granulometric composition of the provided powder sample was determined by laser diffraction, implemented on the Fritsch NanoTec “ANALISETTE 22” laser particle analyzer. Data analysis shows that almost all phases of the technological process determine the microclimate of the internal environment and in the inter-hull zone during emission dispersion. The degree of exposure depends on the dispersion and chemical composition of the dust, in particular, in the air, the dust is oxidized to form a SiO2 film. In addition, there are other harmful substances in the workshop air that can be deposited on dust particles, which makes dust more dangerous and in this case it is necessary to take into account more stringent values of maximum permissible concentrations (MPC). An increase in the SiO2 content tightens the requirements for the cleanliness of the air in the working area. In the work, on the basis of theoretical and experimental data, the most dangerous areas with the formation of industrial dust from the standpoint of environmental risk were identified, the dust dispersion was assessed, the dust collection system was finalized, and a wet cleaning system was installed.

Comprehensive research method for explosive coal dust

The article briefly analyses the explosion and fire hazard properties of coal dust of different dispersions. It is emphasised that many experts working in the field of explosion protection and industrial safety pay insufficient attention to changes in the properties of the dust when reducing its dispersity. It is suggested to develop a new, complex methodology based on the dispersed composition of coal dust. The authors suggest to put methods of special sample preparation and dispersing of samples in two stages as a basis of the complex methodology. To do research with the help of thermal synchronous analysis of the smaller fractions, the authors propose to regrind the coal fraction obtained after the cone crusher in an analytical mill. To exclude adhesion of particles due to the process of static charges accumulation it is suggested to use impactless sieving machine of Retsch company which allows to take out the accumulated charges of static electricity. The coal dust fractions obtained after sieving were sent for granulometric analysis by a dynamic image processing method in CAMSIRE and by an optical microscopic method using a LEICA DM 4000 with image scope colour processing. A simultaneous thermal analysis was performed selectively for fractions smaller than 1000 μm. This was carried out with an STA 449 F3 and NETZSCH Proteus termal analysis application software. The authors consider that the obtained results allow to conclude that it is further expedient to carry out research work in this direction and will make it possible to develop recommendations aimed at prevention of coal dust aerosol explosions.

Sources, pathways and concentrations of potentially toxic trace metals in home environments

Despite ongoing concerns about trace metal and metalloid (trace metals) exposure risks from indoor dust, there has been limited research examining their sources and relationship to outdoor soils. Here we determine the concentrations and sources for potentially toxic trace metals arsenic (As), chromium (Cr), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) and their pathways into homes in Sydney, Australia, using home-matched indoor dust (n = 166), garden soil (n = 166), and road dust samples (n = 51). All trace metals were more elevated indoors versus their matched garden soil counterparts. Indoor Cu and Zn dust concentrations were significantly more enriched than outdoor dusts and soils, indicating indoor sources were more relevant for these elements. By contrast, even though Pb was elevated in indoor dust, garden soil concentrations were correspondingly high, indicating that it remains an important source and pathway for indoor contamination. Elevated concentrations of As, Pb and Zn in garden soil and indoor dust were associated with home age (>50 years), construction materials, recent renovations and deteriorating interior paint. Significant correlations (p < 0.05) between road dust and garden soil Cu concentrations, and those of As and Zn in soil and indoor dust, and Pb across all three media suggest common sources. Scanning electron microscopy (SEM) analysis of indoor dust samples (n = 6) showed that 57% of particles were derived from outdoor sources. Lead isotopic compositions of soil (n = 21) and indoor dust (n = 21) were moderately correlated, confirming the relevance of outdoor contaminants to indoor environments. This study illustrates the source, relationship and fate of trace metals between outdoor and indoor environments. The findings provide insight into understanding and responding to potentially toxic trace metal exposures in the home environment.

Interstellar 2175 &amp;Aring; extinction bump

<p indent="0mm">The interstellar extinction curve contains important information about the chemical composition and size distribution of interstellar dust. The <sc>2175 Å</sc> extinction bump is the most prominent spectral feature on the interstellar extinction curve. Ever since its first detection in 1965, it is well recognized that although the strength of the <sc>2175 Å</sc> extinction bump varies with astrophysical environments, its peak wavelength is invariant and is independent of environmental conditions. We derived the UV extinction curves for 26 interstellar lines of sight based on data from the International Ultraviolet Explorer (IUE) and the Kurucz stellar model atmospheric spectra. It is found that the central wavelength of the <sc>2175 Å</sc> extinction bump of these interstellar lines of sight is not invariant around <sc>2175 Å.</sc> Instead, it exhibits considerable variation in the <sc>2130–2300 Å</sc> wavelength range, in stark contrast to the over-half-a-century-long, common belief of a stable peak wavelength of <sc>2175 Å</sc> for the extinction bump. The new observational property that the central wavelength of the <sc>2175 Å</sc> extinction bump is not constant imposes a new constraint on identifying the bump carrier.

EmulART: Emulating radiative transfer—a pilot study on autoencoder-based dimensionality reduction for radiative transfer models

Dust is a major component of the interstellar medium. Through scattering, absorption and thermal re-emission, it can profoundly alter astrophysical observations. Models for dust composition and distribution are necessary to better understand and curb their impact on observations. A new approach for serial and computationally inexpensive production of such models is here presented. Traditionally these models are studied with the help of radiative transfer modelling, a critical tool to understand the impact of dust attenuation and reddening on the observed properties of galaxies and active galactic nuclei. Such simulations present, however, an approximately linear computational cost increase with the desired information resolution. Our new efficient model generator proposes a denoising variational autoencoder (or alternatively PCA), for spectral compression, combined with an approximate Bayesian method for spatial inference, to emulate high information radiative transfer models from low information models. For a simple spherical dust shell model with anisotropic illumination, our proposed approach successfully emulates the reference simulation starting from less than 1% of the information. Our emulations of the model at different viewing angles present median residuals below 15% across the spectral dimension and below 48% across spatial and spectral dimensions. EmulART infers estimates for sim 85% of information missing from the input, all within a total running time of around 20 minutes, estimated to be 6times faster than the present target high information resolution simulations, and up to 50times faster when applied to more complicated simulations.

Dust explosion in fusion reactors: Explosion characteristics and reaction mechanism of tungsten micro-powder

The explosion of in-vessel dusts, mainly produced by energetic plasma and wall interaction, will pose a great threat to the safe operation of a fusion reactor. Unlike dust explosions in traditional industrial systems, dust explosion in tokamak devices has the unique characteristics, including dust composition (tungsten is one of the main components), initial conditions of explosion, etc. However, the experimental data on this aspect are very few, which is not enough to support the safety assessment of fusion reactors. In this work, the experiments were used to study the explosion characteristics and mechanism of the micro-tungsten in a 20 L spherical vessel. Results showed that the lower explosion limit (LEL) of 2 µm tungsten dust was in the range of 250–500 g/m3, and the maximum explosion pressure would reach 0.46 MPa at 3000 g/m3. The factors related to fusion reactor environment, including initial pressure, ignition energies and the ignition delay time, were studied to demonstrate a significant effect on explosion parameters. The explosion product changed from WO3 to WO2.72 with the increase of nominal dust concentration. A combustion mechanism for single mirco-tungsten particle was established. Based on the experimental data, the explosion possibility and hazard of tungsten dust in fusion reactor were also dicussed.

Quantifying the dust in SN 2012aw and iPTF14hls with ORBYTS

ABSTRACT Core-collapse supernovae (CCSNe) are capable of producing large quantities of dust, with strong evidence that ejecta dust masses can grow significantly over extended periods of time. Red–blue asymmetries in the broad emission lines of CCSNe can be modelled using the Monte Carlo radiative transfer code damocles, to determine ejecta dust masses. To facilitate easier use of damocles, we present a Tkinter graphical user interface (GUI) running damocles. The GUI was tested by high school students through the Original Research By Young Twinkle Students programme, who used it to measure the dust masses formed at two epochs in Type IIP CCSNe, SN 2012aw and iPTF14hls, demonstrating that a wide range of people can contribute to scientific advancement. Bayesian methods quantified uncertainties on our model parameters. From the red scattering wing in the day 1863 Hα profile of SN 2012aw, we constrained the dust composition to large (radius &amp;gt;0.1 μm) silicate grains, with a dust mass of $6.0^{+21.9}_{-3.6}\times 10^{-4}~\mathrm{ M}_\odot$. From the day 1158 Hα profile of SN 2012aw, we found a dust mass of $3.0^{+14}_{-2.5}\times 10^{-4}$ M⊙. For iPTF14hls, we found a day 1170 dust mass of 8.1$^{+81}_{-7.6}\times 10^{-5}$ M⊙ for a dust composition consisting of 50 per cent amorphous carbon and 50 per cent astronomical silicate. At 1000 d post-explosion, SN 2012aw and iPTF14hls have formed less dust than the peculiar Type II SN 1987A, suggesting that SN 1987A may have formed a larger dust mass than typical Type IIP’s.

Fractional Composition and Toxicity Coal–Rock of PM10-PM0.1 Dust near an Opencast Coal Mining Area and Coal-Fired Power Station

This study is aimed at elucidating the fractional composition, volume and toxicity of dust that is deposited in the snow cover for the period of snow accumulation at different distances from coal mines and a coal-fired power station in the Kemerovo region (Russia). During the filtration process, fractions of 10–0.1 µm and less than 0.1 µm were isolated and weighed. Light microscopy was used to estimate the size of dust particles in the 10–0.1 µm fraction. We found that the total volume and fractional composition of dust has no significant trend to change in the research space. The dust contamination is associated mainly with PM2 particles. Genotoxic tests on cell lines A549 and MRC-5 with different concentrations of dust showed high toxicity (including control points). Taking into account the fact that an increase in the concentration of PM leads to intensification in the toxicity of dust, we can determine that the territory within the studied boundaries is dangerous for the population. Our study is important for understanding the processes of formation, toxicity, transport and sedimentation in the snow cover from dust generated in the process of coal mining and the operation of a coal-fired power station.

The Polstar high resolution spectropolarimetry MIDEX mission

The Polstar mission will provide a space-borne 60 cm spectropolarimeter operating at ultraviolet (UV) wavelengths, capturing all four Stokes parameters (intensity, two linear polarization components, and circular polarization). Polstar’s capabilities are designed to meet its goal of determining how circumstellar gas flows alter and inform massive star evolution, affect the stellar remnant population, and stir and enrich the interstellar medium (ISM). These will be achieved by investigating the dynamical geometries in the winds and disks of hot stars, the composition and magnetic alignment of interstellar dust, and the star-forming accretion disks of UV-bright stars at an important transition boundary. Together these areas map out a kind of two-way interface between massive stars and their effect on our galaxy, wherein the stellar winds enrich the ISM with metals and kinetic energy, preconditioning their environment and the stellar endpoints prior to undergoing supernova. The ISM dust in turn reveals the composition and magnetic environment leading to new star formation, and the accretion disks of Herbig Ae/Be stars reveal how the ISM gas returns to make new massive stars. Polstar will combine high-resolution spectroscopy in the time domain with high-precision UV polarimetry. Doppler-shifted UV resonance line opacity will provide information about circumstellar kinematics, while polarization gives complementary geometric information about unseen structures. The composition and magnetic alignment of the smallest interstellar dust grains provides a probe of the ISM utilizing radiative alignment theory (RAT). Polstar will operate in the far-UV (FUV) at 122–200 nm at high spectral resolution of around \(R \sim 30k\), and at FUV and near-UV (NUV) wavelengths of 122–320 nm at lower spectral resolutions of \(0.1-1k\). Detection of polarization levels as weak as 0.1% are expected, with a temporal cadence ranging from 5–10 minutes for most wind variability studies, to hours or days for sampling rotation, to days or weeks for sampling binary orbits, to months to a year for sampling substructure in the inner regions of protoplanetary disks. Sub-meter-class aperture is well suited to access this wide array of time domain science, made possible by restricting to a few hundred bright, massive stars, necessarily extincted by a small to moderate column of interstellar dust, informing both the attributes of the stars and the ISM through which they are seen. As such, the focus is on our own galaxy and its evolutionary drivers, but a few targets in the Magellanic clouds offer the potential to extend this understanding to low-metallicity environments.

Ultraviolet spectropolarimetry with polstar: interstellar medium science

Continuum polarization over the UV-to-microwave range is due to dichroic extinction (or emission) by asymmetric, aligned dust grains. Scattering can also be an important source of polarization, especially at short wavelengths. Because of both grain alignment and scattering physics, the wavelength dependence of the polarization, generally, traces the size of the aligned grains. Similarly because of the differing wavelength dependencies of dichroic extinction and scattering polarization, the two can generally be reliably separated. Ultraviolet (UV) polarimetry therefore provides a unique probe of the smallest dust grains (diameter< 0.09~upmu text{m}), their mineralogy and interaction with the environment. However, the current observational status of interstellar UV polarization is very poor with less than 30 lines of sight probed. With the modern, quantitative and well-tested, theory of interstellar grain alignment now available, we have the opportunity to advance the understanding of the interstellar medium (ISM) by executing a systematic study of the UV polarization in the ISM of the Milky Way and near-by galaxies. The Polstar mission will provide the sensitivity and observing time needed to carry out such a program (probing hundreds of stars in the Milky Way and dozens of stars in the LMC/SMC), addressing questions of dust composition as a function of size and location, radiation- and magnetic-field characteristics as well as unveiling the carrier of the 2175 Å extinction feature. In addition, using high-resolution UV line spectroscopy Polstar will search for and probe the alignment of, and polarization from, aligned atoms and ions - so called “Ground State Alignment”, a potentially powerful new probe of magnetic fields in the diffuse ISM.

The Urmia playa as a source of airborne dust and ice-nucleating particles – Part 2: Unraveling the relationship between soil dust composition and ice nucleation activity

Abstract. Ice-nucleating particles (INPs) originating from deserts, semi-arid regions, and dried lakebeds may cause heterogeneous ice nucleation, impacting cloud properties. Recently, due to climate change and water scarcity, abandoned agricultural lands with little surficial crust and negligible vegetation cover have become an increasing source of atmospheric dust worldwide. Unlike deserts, these areas are rich in soluble salt and (bio-)organic compounds. Using soil samples from various sites of the Lake Urmia playa (LUP) in northwestern Iran and airborne dusts collected at nearby meteorological stations, we elucidate how minerals, soluble salts, and organic matter interact to determine the IN activity of saline soils and dust. X-ray powder diffraction shows that the mineralogical composition is dominated by K-feldspars (microcline), quartz, carbonates, and clay minerals. The samples were stripped stepwise of organic matter, carbonates, and soluble salts. After each removal step, the ice nucleation (IN) activity was quantified in terms of onset freezing temperatures (Thet) and heterogeneously frozen fractions (Fhet) by emulsion freezing experiments using differential scanning calorimetry (DSC). We examined the influence of soluble salts and pH on microcline and quartz in emulsion freezing experiments, comparing these with reference suspensions of microcline and quartz exposed to salt concentrations and pH levels characteristic of the LUP samples. These analyses, combined with correlations between Thet and Fhet, allow us to identify the components that contribute to or inhibit IN activity. The LUP dusts turn out to be very good INPs, with freezing onset temperatures around 248 K in immersion freezing experiments. Interestingly, their IN activity proves to be dominated by the relatively small share of (bio-)organic matter (1 %–5.3 %). After organic matter removal, the remaining IN activity (Thet≈244 K) can be traced back to the clay fraction, because Thet and Fhet correlate positively with the clay mineral content but negatively with quartz and microcline. We attribute the inability of quartz and microcline to act as INPs to the basic pH of the LUP samples as well as to the presence of soluble salts. After additionally removing soluble salts and carbonates, the IN activity of the samples increased again significantly (Thet≈249 K), and the negative correlation with quartz and microcline turned into a slightly positive one. Removing carbonates and salts from the natural samples leads to an increase in Thet and Fhet as well, indicating that their presence also suppresses the IN activity of the (bio-)organic INPs. Overall, this study demonstrates that mineral and organic INPs do not just add up to yield the IN activity of soil dust but that the freezing behavior is governed by inhibiting and promoting interactions between the components.

Mid-infrared Polarization of the Diffuse Interstellar Medium toward CygOB2-12

We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, with A V ≈ 10 mag of foreground extinction, is a benchmark in the study of the properties of dust in the diffuse interstellar medium. The 8–13 μm spectropolarimetry, obtained with the CanariCam multimode camera at the Gran Telescopio CANARIAS shows clear trends with wavelength characteristic of silicate grains aligned in the interstellar magnetic field. The maximum polarization, detected with 7.8σ statistical significance near 10.2 μm, is (1.24 ± 0.28)% with position angle 126° ± 8°. We comment on these measurements in the context of recent models for the dust composition in the diffuse interstellar medium.