Surface Dust Research Articles

Effect of different types of surfactants adsorption characteristics on the wettability of coking coal dust

To investigate the effect of different types of surfactants adsorption characteristics on the wettability of coking coal dust, Guoyang coking coal and three different surfactants - dodecyl dimethyl benzyl ammonium chloride (DDBAC), sodium alcohol ether sulphate (AES), coconut diethanolamide (CDEA) - were used. Firstly, the amount of surfactant adsorbed on coal dust were determined using spectrophotometry. Secondly, the contact angles of surfactants on coal tablets was determined. Subsequently, the relationship between the amount of surfactant adsorbed on the coal dust surface and the contact angle was analysed. Finally, the influence mechanism of the amount of the surfactant adsorbed on the coking coal dust surface on wettability was discussed. The experimental results suggest that the adsorption isotherm of cationic surfactant DDBAC on the coal dust surface is bilayer LS-type, while the adsorption isotherm of anionic surfactant AES and non-ionic surfactant CDEA are L-type and S-type, respectively. Additionally, when the concentration of the solution was 0.05%, the amount of AES adsorbed on the coking coal dust surface was estimated to be 64.9 mgg−1, which was 4.19-fold higher than DDBAC (i.e. to 15.5 mgg−1) and 2.2-fold higher than CDEA (i.e. to 29.5 mgg−1), nearly reaching adsorption saturation. The R2 of the amount of DDBAC, AES, and CDEA adsorbed on the coal dust surface affecting the contact angle was 0.9944, 0.99238, and 0.9923, respectively. The adsorption amount of anionic surfactant AES on the coal dust surface at 0.05% is 64.9 mgg−1, and the adsorption isotherm of surfactant on the coal dust surface is L-type, which is more conducive to enhancing the wettability of coking coal dust. Thus, the amount and adsorption isotherm form of the surfactant adsorbed on the coal dust surface are critical factors affecting the coal dust wettability, which provides a theoretical basis for the reasonable selection of surfactants to improve the coal dust suppression efficiency.

Nonlinear Outcome of Coagulation Instability in Protoplanetary Disks. II. Dust-ring Formation Mediated by Backreaction and Fragmentation

In our previous work (Paper I), we demonstrated that coagulation instability results in dust concentration against depletion due to the radial drift and accelerates dust growth locally. In this work (Paper II), we perform numerical simulations of coagulation instability taking into account effects of backreaction to gas and collisional fragmentation of dust grains. We find that the slowdown of the dust drift due to backreaction regulates dust concentration in the nonlinear growth phase of coagulation instability. The dust-to-gas surface density ratio increases from 10−3 up to ∼10−2. Each resulting dust ring tends to have a mass of ≃0.5 M ⊕ − 1.5 M ⊕ in our disk model. In contrast to Paper I, the dust surface density profile shows a local plateau structure at each dust ring. In spite of the regulation at the nonlinear growth, the efficient dust concentration reduces their collision velocity. As a result, dust grains can grow beyond the fragmentation barrier, and the dimensionless stopping time reaches unity, as in Paper I. The necessary condition for the efficient dust growth is (1) weak turbulence of α < 1 × 10−3 and (2) a large critical velocity for dust fragmentation (>1 m s−1). The efficient dust concentration in outer regions will reduce the inward pebble flux and is expected to decelerate the planet formation via the pebble accretion. We also find that the resulting rings can be unstable to secular gravitational instability (GI). The subsequent secular GI promotes planetesimal formation. We thus expect that a combination of these instabilities is a promising mechanism for dust-ring and planetesimal formation.

Toward Detecting Biosignatures of DNA, Lipids, and Metabolic Intermediates from Bacteria in Ice Grains Emitted by Enceladus and Europa.

The reliable identification of biosignatures is key to the search for life elsewhere. On ocean worlds like Enceladus or Europa, this can be achieved by impact ionization mass spectrometers, such as the SUrface Dust Analyzer (SUDA) on board NASA's upcoming Europa Clipper mission. During spacecraft flybys, these instruments can sample ice grains formed from subsurface water and emitted by these moons. Previous laboratory analog experiments have demonstrated that SUDA-type instruments could identify amino acids, fatty acids, and peptides in ice grains and discriminate between their abiotic and biotic origins. Here, we report experiments simulating impact ionization mass spectra of ice grains containing DNA, lipids, and metabolic intermediates extracted from two bacterial cultures: Escherichia coli and Sphingopyxis alaskensis. Salty Enceladan or Europan ocean waters were simulated using matrices with different NaCl concentrations. Characteristic mass spectral signals, such as DNA nucleobases, are clearly identifiable at part-per-million-level concentrations. Mass spectra of all substances exhibit unambiguous biogenic patterns, which in some cases show significant differences between the two bacterial species. Sensitivity to the biosignatures decreases with increasing matrix salinity. The experimental parameters indicate that future impact ionization mass spectrometers will be most sensitive to the investigated biosignatures for ice grain encounter speeds of 4-6 km/s.

Modeling a severe wintertime Asian dust event observed in the East Asia region: Sensitivity of the WRF-Chem dust emission schemes

This study investigates the capability of the Weather Research and Forecasting-Chemistry (WRF-Chem) model in modeling a severe wintertime Asian dust event, which originated from the East Asia dust source region during 20–22 February 2015. The WRF-Chem simulations were conducted changing with the five embedded dust emission schemes of the UC01, UC04, UC11, GO01, and GA19 schemes. The model reasonably simulated meteorological fields, capturing the characteristic meteorological features over the dust source regions during the severe wintertime Asian dust event. A good meteorological comparison led to the reasonable simulation of the occurrence and transport of the Asian dust plumes, comparing well with the surface dust occurrence reports and the satellite-detected dust signals of aerosol optical depth (AOD) and extinction coefficient. However, considerable (approximately fivefold) differences existed in the dust emission amounts simulated by the different dust emission schemes. From the model-measurement comparison of surface PM10 concentration, it was found that the UC01 and UC04 schemes could simulate the severe wintertime Asian dust plumes in the dust source regions, capturing the dust occurrence timing and the concentration level reasonably. However, the performance of the schemes significantly depended on near-surface wind speed and soil moisture amount. On the contrary, the UC11, GO01, and GA19 schemes failed to simulate the dust plumes, revealing intrinsic limitations for severe wintertime dust plume simulation. Furthermore, this study suggests the realistic representation of the Asian dust source region and the inclusion of frozen soil parameterization in the WRF-Chem model to predict severe wintertime Asian dust events realistically.

Aqueous alteration of the Vastitas Borealis Formation at the Tianwen-1 landing site

The Vastitas Borealis Formation is a Hesperian-aged sedimentary unit that mainly covers the Martian northern plains. Its environment of formation is uncertain but may be related to an ancient Martian ocean, outflow channel deposits, compaction and drainage activities, or subsurface ice-related processes. Here we investigate the geological evolution of the Vastitas Borealis Formation using geochemical and mineralogical data acquired by the Mars Surface Composition Detector on board the Zhurong rover at the Tianwen-1 landing site. We find that the fine-grained soil is very similar to the ubiquitous surface dust at other landing sites on Mars but mixed with calcium-rich and magnesium-poor local materials. These materials are mostly igneous minerals mixed with allophane and imogolite/opal and appear to have a low degree of chemical alteration. We suggest that these deposits likely formed by alteration of extensive volcaniclastic soils in limited or ephemeral water under cold conditions, which largely supports the hypotheses of a frozen ocean and sublimation.

Quantum mechanical modeling of interstellar molecules on cosmic dusts: H2O, NH3, and CO2.

Since the first detection of CH molecule in interstellar medium (ISM), more than 270 molecules have been identified in various astronomical sources in ISM. These molecules include big complex ones, such as fullerene (C60) and polycyclic aromatic hydrocarbons (PAHs), which are the main components of carbonaceous dust. Dust surface chemistry plays an important role in explaining the formation of interstellar molecules. However, many of the dust surface chemical parameters, such as the adsorption energies, are still of uncertainty. Here we present a study of the adsorption of water (H2O), ammonia (NH3), and carbon dioxide (CO2) on graphene-like substrate within the framework of density functional theory (DFT). We used Gaussian 16 software and adopted the corrected generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functions. We determined the optimal accretion position of the studied molecules on the graphene-like surface and calculated the adsorption energies. Furthermore, according to the density of states and molecular orbitals of the adsorbed states, we analyzed the charge transfer between the molecules and the graphene-like surface. These results can provide more accurate parameters for calculating the chemical reaction rates on the dust surface, thus contributing to the understanding of dust-surface reactions in ISM.

Influence of Xenon–Fluorine–Sulfur Hexafluoride (Xe+–F−–SF6−) and Argon-Fluorine-Sulfur Hexafluoride (Ar+–F−–SF6−) Streaming on Dust Surface Potential (DSP) That Has Cairn–Tsallis Distributed Plasmas

The dust grain surface potential is examined analytically and numerically in dusty plasmas containing negative/positive ion species by using the Cairn Tsallis (non-Maxwellian) dusty plasma. The equations for the dust-charging process are derived to solve the current balance equation for the xenon–fluorine–sulfur hexafluoride and argon–fluorine–sulfur hexafluoride plasmas. The charging process affected by plasma properties such as spectral indices α and q, in addition to positive ion streaming (UAr+ and UXe+) and negative ion streaming (UF− and USF6−) of both types of plasmas, is examined. Our findings suggest that considering a wide range of Xe+−F−−SF6− and Ar+−F−−SF6− masses is critical for understanding plasma physics, specifically multi-component plasmas.

Partition of phthalates among air, PM2 .5 , house dust and skin in residential indoor environments.

As a group of typical endocrine disrupters, phthalates are simultaneously present in a variety of environmental media and enter human body through multiple exposure pathways. In this study, field monitoring data were used to characterize the skin-air (Klg ), dust-air (Kd ), and PM2.5 -air (Kp ) partition coefficients of DiBP, DnBP, and DEHP. The median values of log(Klg ) in the summer and winter were 7.654 and 7.932, 7.265 and 7.902, 9.419 and 9.015 for DiBP, DnBP, and DEHP, respectively, and Klg was significantly higher in the winter. The median Kd (m3 /mg) in the summer (0.036-0.151 for DiBP, 0.021-0.036 for DnBP and 1.479-4.069 for DEHP) were significantly higher than the counterparts in the winter (0.027-0.065 for DiBP, 0.022-0.245 for DnBP, and 0.140-3.250 for DEHP). In addition, Kd was associated with material of surface and residence time of dust. The Kp values (m3 /μg) of DiBP, DnBP, and DEHP in the summer (0.053, 0.015, and 0.021) were also significantly higher than the counterparts in the winter (0.011, 0.004, and 0.025). The partition of phthalates was influenced by built environment, such as temperature, humidity, ventilation, indoor chemistry, smoking, and building age. Except Klg , there was substantial discrepancy between the estimates of K with empirical equations and the values of K based on field monitoring data in our study.

Physical processes leading to surface erosion and dust particles dynamics of airless bodies

The article is a review of the state of research on physical processes occurring near the surface of airless bodies, in particular, the Moon, asteroids, comets, which lead to their erosion, that is, to the modification of superficial and sometimes even deeper layers. External influences on the bodies are considered—micrometeor streams, solar wind and geomagnetic tail plasma flows, solar electromagnetic radiation, and cosmic rays, which are the main causes of erosion. The main features of airless bodies belonging to different classes are given. The main physical mechanisms that can lead to the release and removal of dust particles from the surface of regolith are analyzed, in particular, the energy aspects of high-speed micrometeor impacts, electrostatic processes of particle release from the surface, and thermodynamic processes occurring in the near-surface layers of cometary nuclei. The conditions for the removal of dust particles from the surface of a rotating body and the conditions under which the body can collapse are considered. Depending on the characteristics of these bodies, the processes of erosion, as well as the causes of its occurrence, can vary significantly. The main unresolved problems associated with the processes of erosion of bodies, which require further research, are considered.

Complementary Mass Spectral Analysis of Isomeric O-bearing Organic Compounds and Fragmentation Differences through Analog Techniques for Spaceborne Mass Spectrometers

Mass spectrometers on board spacecraft typically use either impact ionization or electron ionization (EI) as ion sources. Understanding the similarities and differences in the spectral signatures and fragmentation patterns produced by different techniques in mass spectrometry could elucidate the composition of organic compounds. Here we present a comparison between the mass spectra obtained through laser-induced liquid beam ion desorption (LILBID; proven to simulate the impact ionization mass spectra of ice grains) and EI mass spectra of pairs of low-mass, isomeric aldehydes and ketones. Our comparison confirms that EI produces more fragmentation of carbonyl compounds, particularly aldehydes, than LILBID. We find protonated molecular ions [M+H]+ in LILBID but molecular ions [M]+ in EI spectra. From the evaluated species, LILBID generally produces oxygen-carrying fragment ions (e.g., [CHO]+ and [C2H3O]+) in the mass ranges 26–30 and 39–44 u, while in EI, most ions in these ranges correspond to hydrocarbon fragments. The LILBID spectra additionally show mostly protonated oxygen-bearing fragments [CH3O]+ and [C2H5O]+ at m/z 31 and 45, less commonly observed in EI spectra. We observe a decrease in the relative intensities of cation fragment mass lines between m/z 26 and 33 and an increase between m/z 39 and 45, with an increasing carbon number for ketones and aldehydes with LILBID and EI, respectively. Our study provides a basis for complementary compositional analysis to identify the structural properties of organic species in a space environment using different spaceborne mass spectrometers (e.g., SUrface Dust Analyzer and MAss Spectrometer for Planetary EXploration) on board NASA’s future Europa Clipper space mission.

Spectrophotometric properties of materials from the Mars Science Laboratory at Gale crater: 1. Bradbury Landing to Cooperstown

During the first 443 martian days (sols) of the Mars Science Laboratory (MSL) Curiosity rover mission, visible/near-infrared (445–1012 nm) multispectral observations were acquired at different times of sol by the Mast Camera (Mastcam) and Navigation Camera (Navcam) at five locations along the traverse. Measurements of soil, dust, and rock units spanned sufficient incidence, emission, and phase angles to enable radiative transfer models to constrain the surface scattering functions, single-scattering albedo ( w ), and microphysical properties of the units at each site. Although the model results were mainly consistent with previous results from other landing sites, there were some notable exceptions. For example, the less dusty “Blue rocks” units were modeled as more backscattering compared to ostensibly dustier “Red rocks” units, which was opposite to results from other landed missions. Relations between the peak phase angle of phase curve ratios, w values, and macroscopic roughness ( θ ¯ ) suggested that unlike most of the materials observed by the Spirit and Opportunity rovers, the effects of particle-scale roughness and internal scattering were a greater influence on MSL units than surface scattering. Also noteworthy were unique photometric signatures modeled from data acquired at the landing site on Sol 20 as part of the first in situ spectrophotometric analyses of materials subjected to erosion and/or surface dust removal from spacecraft descent engines. Modeled w spectra were relatively flat and dark for the Sol 20 Blue rocks unit and were positively correlated with average θ ¯ values, similar to some laboratory studies of coarse-grained and/or glassy mafic materials. While low w values and backscattering behaviors were modeled for the Sol 20 “Regolith” unit, the more heavily scoured, lighter-toned regions included soils with extremely forward scattering behaviors, large w values, and that lacked ferric absorption features. The absence of phase reddening effects in all the Sol 20 units likely also was caused by surface disruptions during the landing. Future analyses of additional spectrophotometric data sets from both Curiosity and the Mars 2020 Perseverance rover will continue to yield important comparisons among the variable scattering properties of martian geologic units. • Five sites imaged by MSL Mastcam/Navcam at multiple times-of-sol during Sols 20- 443. • Less dusty rocks modeled as more backscattering compared to redder, dustier rocks. • Small-scale roughness, internal scattering stronger influence than surface scattering. • Unique photometric signatures at landing site due to effects of lander descent plumes.

Formation of H2CO and CH3OH in the Protoplanetary Disks

It is known that the complex organic molecules in planetary systems may be formed by the organic chemistry of gases and particles in protoplanetary disks. Among these molecules, H2CO and CH3OH are potential precursors of essential organic compounds like glycolaldehyde. We calculate the physical and chemical structures of the protoplanetary disks around LkCa 15 and MWC 480 stars, compare the obtained column densities with the observed values. Our results mostly show reasonable agreements with observations. We identify the formation of H2CO to be through the both gas-phase and dust surface reactions, while CH3OH is dominantly formed by surface chemistry in the original astrolabe and then released into the gas-phase by surface exothermic chemical reactions in the LkCa 15 disk. We studied the synthesis of complex organic molecules (NH2CHO and CH3OCHO) in the protoplanetary disk to predict the observable species and Molecular abundance. In the disks around LkCa 15 and MWC 480 stars, we suggest that the strong spectral line observation of NH2CHO belonging to band 4 may obtain good results with ALMA, the observation of CH3OCHO may be challenging.

Predicting solar photovoltaic electrical output under variable environmental conditions: Modified semi-empirical correlations for dust

The current study investigated the simultaneous impacts of dust as well as other environmental parameters on cell temperature and the electrical outputs of photovoltaic systems. Based on the experimental and analytical analysis, several linear and polynomial semi-empirical correlation forms were proposed. It was shown that cell temperature depends directly on irradiation and ambient temperature, as well as inversely on humidity, wind speed, and the amount of accumulated dust on the surface. During the four-year outdoor experiments and further indoor measurements, the surface dust density varied from 0 to 10.1174 g.m−2, which resulted in up to a 28 % current loss. Although, it was shown that dust affects the output voltage less, and the most recorded variation was <0.5 % reduction. The electrical behavior of the photovoltaic system was also simulated with a modified single-diode model. Comparing the simulation results, correlation predictions, and experimental measurements confirmed consistency. Moreover, it was shown that considering the prediction precision, simplicity, and computational cost, the proposed correlation forms should be preferred when just the output current, voltage, and power are of concern. The proposed modified semi-empirical correlation forms can be easily coupled with other models to improve their precision and accuracy.

Droplet breakup in electrostatic spray based on multiple physical fields

A droplet breakup model was proposed for simulating electrostatic spray in multiple physical fields. The static electricity, laminar flow and droplet atomization in COMSOL Multiphysics were coupled completely, and a two-dimensional simulation model was established. The process of droplet breakup and movement of electrostatic spray was revealed under the action of electric field, gravity field and air field. The electric field distribution under the needle ring electrode configuration was studied. The effects of different electrostatic voltage, needle ring distance and ring electrode diameter on droplet breakup characteristics, distribution uniformity and charge characteristics were analyzed. When the electrostatic voltage is -6 ∼ -7 kV, the needle ring distance is 4 mm, and the ring electrode diameter is 30 mm, the electrostatic spray effect is better, and the density standard deviation is as low as 0.04528 /mm2, 0.0559 /mm2 and 0.06016 /mm2, respectively. Electrostatic spray has the characteristics of refining droplets, improving the uniformity of droplets distribution and controlling spray morphology, which provides a strong basis for the application of electrostatic spray in surface film preparation, dust removal, fuel injection and other practical engineering fields.

Reactive Uptake of Gas-Phase NO2 by Urban Road Dust in the Dark.

Road dust constitutes a prominent source of anthropogenic particulate matter, making its heterogeneous interactions with common atmospheric gas-phase compounds important. Here, we show that three distinct samples of urban road dust-including dust samples collected from city streets in summer and winter, and an urban park in summer-react with NO2 in the dark, forming NO and surface nitrite. The loss of NO2 ranged from ∼2 to 13% of its gas-phase concentration and scaled with its concentration as well as with the mass of the road dust sample. The uptake of NO2 by the winter dust was ∼4 times greater than that seen from summer street dust, which was in turn greater than that by the park dust. The conversion ratio of NO2 → NO ranged from 0.06 to 0.8 NO produced per NO2 lost and was greatest for the summer park dust. Exposure of the summer road dust to NO2 roughly doubles the concentration of inorganic nitrite anion in the dust but does not produce nitrate. The formation of NO and photolabile nitrite products means that heterogeneous NO x reactions occurring on the surface of road dust in the dark could have wide implications for the oxidative potential of urban areas.

Significant formation of sulfate aerosols contributed by the heterogeneous drivers of dust surface

Abstract. The importance of dust heterogeneous oxidation in the removal of atmospheric SO2 and formation of sulfate aerosols is not adequately understood. In this study, the Fe-, Ti-, and Al-bearing components, Na+, Cl−, K+, and Ca2+ of the dust surface, were discovered to be closely associated with the heterogeneous formation of sulfate. Regression models were then developed to make a reliable prediction of the heterogeneous reactivity based on the particle chemical compositions. Further, the recognized gas-phase, aqueous-phase, and heterogeneous oxidation routes were quantitatively assessed and kinetically compared by combining the laboratory work with a modelling study. In the presence of 55 µg m−3 airborne dust, heterogeneous oxidation accounts for approximately 28.6 % of the secondary sulfate aerosols during nighttime, while the proportion decreases to 13.1 % in the presence of solar irradiation. On the dust surface, heterogeneous drivers (e.g. transition metal constituents, water-soluble ions) are more efficient than surface-adsorbed oxidants (e.g. H2O2, NO2, O3) in the conversion of SO2, particularly during nighttime. Dust heterogeneous oxidation offers an opportunity to explain the missing sulfate source during severe haze pollution events, and its contribution proportion in the complex atmospheric environments could be even higher than the current calculation results. Overall, the dust surface drivers are responsible for the significant formation of sulfate aerosols and have profound impacts on the atmospheric sulfur cycling.

Heavy Metal Pollution and Risk Assessment of Surface Dust in the Arid NW China.

High concentrations of heavy metals (HMs) in urban surface dust (USD) can be extremely hazardous to urban ecology and human health. Oasis cities are located at the edge of deserts and are more exposed to salt/sandstorms, and they face a significantly higher accumulation of USD than wet or semi-humid areas. However, systematic studies on the pollution and risk assessment of HMs in USD in oasis cities have rarely been conducted. This study systematically analyzed the enrichment status, spatial distribution, pollution levels, health risks, and sources of HMs in USD in a typical oasis city (Changji city). The results showed that the average concentrations of Pb, Ni, As, Cd, Hg, and Cu in the USD of Changji city were 46.83, 26.35, 9.92, 0.21, 0.047, and 59.33 mg/kg, respectively, and the results of the pollution index evaluation showed moderate Pb, Hg, and Cu pollution, mild Cd pollution, and no Ni or As pollution. The spatial distribution of HM concentrations in the USD was substantially heterogeneous. High values of Pb, Hg, and Cu concentrations were mainly observed in areas with relatively intensive transportation and commercial activities, and high values of Cd and Ni were observed in industrial areas. The health risk assessment showed that HMs do not pose non-carcinogenic risks to humans at their current level, but they pose a carcinogenic risk to children, with As contributing the largest carcinogenic and non-carcinogenic risks. The source identification of HMs showed that the main pollution of HMs were traffic sources for Pb and Cu, industrial sources for Ni and Cd, natural sources for As, and coal-fired sources for Hg. According to the results of the quantitative analysis with the positive matrix factorization, the contribution of pollution sources followed this order: industrial sources (31.08%) > traffic sources (26.80%) > coal-fired sources (23.31%) > natural sources (18.81%).

Color and spectral characteristics of long-lived meteor trail formed by the Tunka bolide

The paper addresses color characteristics and possible spectral composition of emission of a long-lived (~40 min) meteor trail of uncommon geometry, which was formed due to the bolide passage in the Tunka Valley on November 17, 2017. Analysis of dynamics of RGB channels of the meteor trail colored image shows that during the first ~8 minutes the meteor trail emission might have been contributed by the ionization trail. The ionization trail was formed by particles of the meteor matter neutral and ionized components that were heated to high temperatures on the surface of the main meteoroid and separated from it. We also examine the discussed mechanism of heterogeneous chemical reactions occurring on the surface of meteoric dust (FeS, FeO, etc.) with participation of atoms and molecules of atmospheric gases. The yellowish color of the Tunka bolide meteor trail was assumed to be determined, first of all, by the emission of molecular nitrogen N₂ band within the 570–750 nm spectral range (the first positive system) and/or enhancement of NO*₂ continuum in heterogeneous chemical reactions. The meteor trail emission spectrum should also include relatively bright atomic lines and molecular bands of the meteoric matter and atmospheric gases FeI, MgI, CaI, SiI, NaI, FeO and SO₂, OI, OH, etc.

Цветовые и спектральные характеристики долгоживущего метеорного следа, образованного Тункинским болидом

The paper addresses color characteristics and possible spectral composition of emission of a long-lived (~40 min) meteor trail of uncommon geometry, which was formed due to the bolide passage in the Tunka Valley on November 17, 2017. Analysis of dynamics of RGB channels of the meteor trail colored image shows that during the first ~8 minutes the meteor trail emission might have been contributed by the ionization trail. The ionization trail was formed by particles of the meteor matter neutral and ionized components that were heated to high temperatures on the surface of the main meteoroid and separated from it. We also examine the discussed mechanism of heterogeneous chemical reactions occurring on the surface of meteoric dust (FeS, FeO, etc.) with participation of atoms and molecules of atmospheric gases. The yellowish color of the Tunka bolide meteor trail was assumed to be determined, first of all, by the emission of molecular nitrogen N₂ band within the 570–750 nm spectral range (the first positive system) and/or enhancement of NO*₂ continuum in heterogeneous chemical reactions. The meteor trail emission spectrum should also include relatively bright atomic lines and molecular bands of the meteoric matter and atmospheric gases FeI, MgI, CaI, SiI, NaI, FeO and SO₂, OI, OH, etc.

Millimeter gap contrast as a probe for turbulence level in protoplanetary disks

Turbulent motions are believed to regulate angular momentum transport and influence dust evolution in protoplanetary disks. Measuring the strength of turbulence is challenging through gas line observations because of the requirement for high spatial and spectral resolution data, and an exquisite determination of the temperature. In this work, taking the well-known HD 163296 disk as an example, we investigated the contrast of gaps identified in high angular resolution continuum images as a probe for the level of turbulence. With self-consistent radiative transfer models, we simultaneously analyzed the radial brightness profiles along the disk major and minor axes, and the azimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap contrasts measured from these profiles, we constrained the gas-to-dust scale height ratio $\Lambda$ to be $3.0_{-0.8}^{+0.3}$, $1.2_{-0.1}^{+0.1}$ and ${\ge}\,6.5$ for the D48, B67 and B100 regions, respectively. The varying gas-to-dust scale height ratios indicate that the degree of dust settling changes with radius. The inferred values for $\Lambda$ translate into a turbulence level of $\alpha_{\rm turb}\,{<}\,3\times10^{-3}$ in the D48 and B100 regions, which is consistent with previous upper limits set by gas line observations. However, turbulent motions in the B67 ring are strong with $\alpha_{\rm turb}\,{\sim}1.2\,{\times}\,10^{-2}$. Due to the degeneracy between $\Lambda$ and the depth of dust surface density drops, the turbulence strength in the D86 gap region is not constrained.