Dust Spectrum Research Articles

Самоочищение атмосферного воздуха от пылевых частиц в условиях прибрежного морского климата

The intensity of air pollution depends on the characteristics of pollution sources, distance from the sea, terrain, density of residential buildings and the presence of a green zone. The influence of climatic conditions on the distribution of suspended particulate matter in the atmospheric surface layer of Vladivostok was studied. The aim of the study was to determine the particle size distribution of suspended particulate matter in the atmospheric surface layer and to assess the conditions for self-purification of urban air under the influence of the coastal maritime climate. The assessment of the urban air pollution with suspended particulate matter was carried out in two areas with different levels of pollution. The human breathing zone was examined. The temperature, humidity, air pressure, wind direction and speed at sampling points were determined. We used monitoring of meteorological data (dew point, wind gusts, clouds, fog) from the nearest regional meteorological stations. Statistical processing included the “Canonical Analysis” module. In the polluted area of the city the atmospheric circulation (direction, speed and gusts of wind) greatly affect the distribution of fine-dispersed particles (2.5–10.0 µm) that are hazardous to health. The impact of temperature and humidity conditions is reduced in power. The temperature and humidity regime, atmospheric pressure, cloudiness with frequent fog affect the ultrafine dust spectrum in the slightly polluted island area of the city. The above factors contribute to the enhancement of the nanoparticle nucleation process. Self-purification of the air surface layer from dust particles in both polluted and slightly polluted areas of Vladivostok is associated with the southerly winds. The monsoon maritime climate defines the air purifying in the region. The temperature and humidity regime actively affects the dust disperse composition in both sampling sites. In the island area of the city it determines the content of particles up to 10 µm; in the continental area – fractions of 0.1–50.0 µm.

Spectral reflectance of atmospheric dust as an indirect indicator of its soil origin

Atmospheric dust affects both human health and climate change. Therefore, the study of atmospheric dust is one of the important tasks of many scientific fields. The aim of our research was to indirectly assess the relation of atmospheric dust over arable lands of two test sites in Tver and Tula regions of Russia with soils. Dust was analyzed on aspirator filters after pumping specified volumes of air at the level of 20–30 cm above the arable surface. Its spectral reflectance was used as a criterion of soil origin of dust, which was compared with the reflectance of the size fraction (50–200 nm) of soils isolated by dry sieving of a sample of arable soil horizon. The spectral reflectance of dust was calculated based on approaches of linear separation of spectral mixture, taking into account the projective coverage of dust particles on filters, which was determined by analyzing microscope photographs of the filters in GIS. As a result, it was found that the recovered dust spectra on the filters correlate well with the spectra of the same size soil fraction separated by dry sieving, which indirectly confirms the predominance of specifically soil dust on the filters. Spearman correlation coefficient is within the range of 0.84–0.90, Kendall's Tau correlation coefficient varies within 0.70–0.79 (at significance level p < 0.05). Under the conditions of insignificant atmospheric dust load and when collecting a sufficient amount of dust for direct analysis is time and labour consuming, the approach used may serve as an alternative for indirect confirmation of the soil origin of dust in the near ground layer of the atmosphere. In the future, this approach can be used as a basis for monitoring of arable soils deflation.

Radiation Spectral Analysis of 3D Dust Molecular Clusters (PAHs) and Peptoids under Ionization and Electric Field in ISM

Polycyclic aromatic hydrocarbons (PAHs), PANHs, and peptoids dust spectral calculations from the interstellar medium (ISM) are important for dust observations and theory. Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field. We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures. By the Vienna Ab-initio Simulation Package code, the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust. When the radius of spherical dust clusters is ∼[0.009–0.042] μm, the dust radiation spectrum agrees well with the Z = 0.02 mMMP stellar spectra, and the PAHs radiation spectrum of NGC 4676 at wavelengths of (0–5] μm and (5–10] μm, respectively. In the ionized state, the N-PAH, C10H9N, 2(C4H 4)1+, and peptoids 4(CHON), (C8H10N2O5)1+ dust clusters at 3.3 μm, while the 2(C22H21N3O 2)1+, 4(CHON) dust clusters at 5.2 μm have obvious peaks. There is a characteristic of part of PAHs and peptoids clusters radiation at the near-infrared wavelength of 2 μm. However, especially after applying an electric field to the dust, the emission spectrum of the dust increases significantly in the radiation wavelength range [3–10] μm. Consequently, the dust clusters of PAHs, PANHs, and peptoids of the radius size ∼[0.009–0.042] μm are likely to exist in the ISM.

Predictive atmospheric dispersion and deposition characteristics of activated tungsten dust

Tungsten is considered to be the most promising material for plasma-facing components of fusion reactors in addition to other industrial and military uses. Activated tungsten dust produced by plasma-wall interaction and released under accidental conditions would be the emerging environmental pollutant with both chemical and radiation toxicity. For the first time, atmospheric dispersion and deposition characteristics were investigated for tungsten dust with various particle size spectrum similar as generated in fusion reactors. Euler-Lagrange approach was adopted to describe parcels motion and deposition behaviors. Proper numbers of parcels were determined for the atmospheric dispersion and various parcel diameters scale. Near-surface concentration distribution and dry deposition velocity were predicted for tungsten dust with both single size dust and realistic particle size spectrum dust. Influences of chemical forms and release factors on atmospheric dispersion and deposition of tungsten dust were preliminary identified at last. It is indicated that 150 million parcels are needed for 10 μm dust under 5 km scale. Dry deposition velocity of tungsten dust is up to 11.3 cm s−1 and increase along with particle diameter because of its high density and gravitational deposition effect. The critical diameter judging whether gravitational deposition could appear for tungsten dust is 1 µm. Deposited particle size spectrum would be completely different along the downwind distance which would result in differences in subsequent behaviors in other environmental compartments.

Pre and post-landing atmospheric optical depths at the Zhurong landing site on Mars retrieved using a single-image-based approach

The atmosphere of Mars has complex photometric processes due to multiple scattering and absorption by the suspended aerosols. The atmospheric optical depth is an indicator of the aerosol concentrations and can be used to model the contribution of atmospheric scattering, thereby correcting surface spectra. The atmospheric optical depth is also important in analysing the variations of atmospheric dust and evaluating the risks facing landing and roving missions. Retrieving the atmospheric optical depth from a single image is desirable as simultaneous stereo observations of the Martian surface are not common. However, most of the existing single-image-based methods rely on shadows in the image, which can be challenging to identify when the site is smooth or when the atmosphere becomes turbid. In this paper, we present a method of retrieving the atmospheric optical depth from a single image based solely on non-shadowed surfaces. This method was validated using HiRISE images and measurements acquired by rovers on the Martian surface. The method achieved an RMSE of 2%–7% in most cases, depending on the different surface photometric models used. The results indicated that aerosol scattering parameters have less impact on the retrievals than the surface photometric properties, likely due to the fact that the data is optically thin. The optical depths at the Zhurong landing site before and after landing were estimated using the proposed method. The results show that the optical depths first decreased and then increased, with the turning point being around the landing date, indicating that the Zhurong rover landed at an appropriate time. The proposed method is of significance for the analysis of Martian atmospheric dust and surface spectra with better spatio-temporal resolutions.

Aerosol Mineralogical Study Using Laboratory and IASI Measurements: Application to East Asian Deserts

East Asia is the second-largest mineral dust source in the world, after the Sahara. When dispersed in the atmosphere, mineral dust can alter the Earth’s radiation budget by changing the atmosphere’s absorption and scattering properties. Therefore, the mineralogical composition of dust is key to understanding the impact of mineral dust on the atmosphere. This paper presents new information on mineralogical dust during East Asian dust events that were obtained from laboratory dust measurements combined with satellite remote sensing dust detections from the Infrared Atmospheric Sounding Interferometer (IASI). However, the mineral dust in this region is lifted above the continent in the lower troposphere, posing constraints due to the large variability in the Land Surface Emissivity (LSE). First, a new methodology was developed to correct the LSE from a mean monthly emissivity dataset. The results show an adjustment in the IASI spectra by acquiring aerosol information. Then, the experimental extinction coefficients of pure minerals were linearly combined to reproduce a Gobi dust spectrum, which allowed for the determination of the mineralogical mass weights. In addition, from the IASI radiances, a spectral dust optical thickness was calculated, displaying features identical to the optical thickness of the Gobi dust measured in the laboratory. The linear combination of pure minerals spectra was also applied to the IASI optical thickness, providing mineralogical mass weights. Finally, the method was applied after LSE optimization, and mineralogical evolution maps were obtained for two dust events in two different seasons and years, May 2017 and March 2021. The mean dust weights originating from the Gobi Desert, Taklamakan Desert, and Horqin Sandy Land are close to the mass weights in the literature. In addition, the spatial variability was linked to possible dust sources, and it was examined with a backward trajectory model. Moreover, a comparison between two IASI instruments on METOP-A and -B proved the method’s applicability to different METOP platforms. Due to all of the above, the applied method is a powerful tool for exploiting dust mineralogy and dust sources using both laboratory optical properties and IASI detections.

The interstellar dust emission spectrum

Context. Most of the modelling of the interstellar dust infrared emission spectrum is done by assuming some variations around a single-temperature grey-body approximation. For example, the foreground modelling of Planck mission maps involves a single dust temperature, T, along a given line-of-sight with a single emissivity index, β. The two parameters are then fitted and therefore variable from one line-of-sight to the other. Aims. Our aim is to go beyond that modelling in an economical way. Methods. We model the dust spectrum with a temperature distribution around the mean value and show that only the second temperature moment matters. We advocate the use of the temperature logarithm as the proper variable. Results. If the interstellar medium is not too heterogeneous, there is a universal analytical spectrum, which is derived here, that goes beyond the grey-body assumption. We show how the cosmic microwave background radiatively interacts with the dust spectrum (a non-negligible corrective term at millimetre wavelengths). Finally, we construct a universal ladder of discrete temperatures, which gives a minimal and fast description of dust emission spectra as measured by photometric mapping instruments that lends itself to an almost linear fitting. This data modelling can include contributions from the cosmic infrared background fluctuations.

Full-sky, Arcminute-scale, 3D Models of Galactic Microwave Foreground Dust Emission Based on Filaments

Abstract We present the DustFilaments code, a full-sky model for the millimeter Galactic emission of thermal dust. Our model, composed of millions of filaments that are imperfectly aligned with the magnetic field, is able to reproduce the main features of the dust angular power spectra at 353 GHz as measured by the Planck mission. Our model is made up of a population of filaments with sizes following a Pareto distribution ∝ L a − 2.445 , with an axis ratio between short and long semiaxes ϵ ∼ 0.16 and an angle of magnetic field misalignment with a dispersion rms(θ LH) = 10°. On large scales, our model follows a Planck-based template. On small scales, our model produces spectra that behave like power laws up to ℓ ∼ 4000 or smaller scales by considering even smaller filaments, limited only by computing power. We can produce any number of Monte Carlo realizations of small-scale Galactic dust. Our model will allow tests of how the small-scale non-Gaussianity affects CMB weak lensing and the consequences for the measurement of primordial gravitational waves or relativistic light relic species. Our model also can generate frequency decorrelation on the modified blackbody spectrum of dust and is freely adjustable to different levels of decorrelation. This can be used to test the performance of component separation methods and the impact of frequency spectrum residuals on primordial B-mode surveys. The filament density we paint in the sky is also able to reproduce the general level of non-Gaussianities measured by Minkowski functionals in the Planck 353 GHz channel map.

New-generation dust emission templates for star-forming galaxies

Context. The infrared (IR) emission of dust heated by stars provides critical information for galaxy evolution studies. Unfortunately, observations are often limited to the mid-IR, making templates a necessity. Previously published templates were based on small samples of luminous galaxies, which are not necessarily representative of normal star-forming galaxies. Aims. We constructed new-generation dust templates, including instrument-specific relations and software tools that facilitate the estimation of the total IR (TIR) luminosity as well as obscured and unobscured star formation rate (SFR) based on one or several fluxes up to z = 4. For the first time, the templates include a dependence on both TIR luminosity and the specific SFR (sSFR), thereby increasing their reliability and utility for a wide range of galaxies. We also provide formulae for calculating TIR luminosities and SFR from JWST F2100W observations at 0 < z ≲ 2. Methods. Our templates are based on 2584 normal star-forming galaxies spanning a wide range of stellar mass and sSFR, including sSFRs typical at higher redshifts. IR spectra and properties were obtained using CIGALE and the physically motivated Draine & Li (2007, ApJ, 657, 810) dust models. The photometry from the GALEX-SDSS-WISE Legacy Catalog was supplemented with 2MASS and Herschel-ATLAS, up to 19 bands from FUV to 500 μm. Results. The shape of the dust spectrum varies with TIR luminosity, but also independently with sSFR. Remarkably precise estimates of the dust luminosity are possible with a single band over the rest-frame 12−17 μm and 55−130 μm. We validate single-band estimates on diverse populations, including local luminous IR galaxies, and find no significant systematic errors. Using two or more bands simultaneously yields the unbiased estimation of the TIR luminosity, even of star-forming dwarfs. Conclusions. We obtain fresh insights regarding the interplay between monochromatic IR luminosities, spectral shapes, and physical properties, and we constructed new templates and estimators of the dust luminosity and SFR. We provide software for generating templates and estimating these quantities based on 1−4 bands from WISE, JWST, Spitzer, and Herschel, up to z = 4.

Emission Spectrum of Dust in a Cooling Gas

The emission spectrum of dust undergoing substantial temperature fluctuations behind strong shocks (>100 km/s) is modeled. The model includes calculating the temperature distribution function of the dust particles owing to stochastic heating by electrons in the ambient plasma, as well as the features of the resulting spectral distribution of the emission from the dust. As the surrounding plasma cools, the emission spectrum changes and differs noticeably from the “quasi-Planck” spectrum of isothermal dust (or a superposition of spectra of this sort). The character of these changes can be used for diagnostics of the thermal state of the plasma. Objects where these effects can be significant are discussed briefly.

INDUCING INTRINSIC γ-RAY EMISSION OF THE INTERSTELLAR MEDIUM BY INTENSE FLUXES OF PROTONS AND α-PARTICLES IN ACTIVE GALACTIC NUCLEI

Cosmic-ray induced γ-ray emission inactive galactic nuclei (AGN) has been examined in thisstudy for the first time. Cross-sections for the formation ofγ-quanta in such cosmic-ray collisions were selected in the1-150 MeV energy range. Synthetic γ-ray spectra werecomputed for both interstellar gas and dust. At the sameenergies of particle collisions and induced emission of γ-quanta, energy intervals of diagnostic interest weredetermined. Specific characteristics of emission weredetected in the energy ranges of 5-15 MeV and 23-30 MeVfor most investigated elements. Diffuse continuous γ-rayspectra for the other energy ranges were less informativewith regard to the determination of the chemicalcomposition of interstellar gas. It has been shown thatexploring cosmic-ray fluxes in the vicinity of galacticcentres by employing the examined γ-ray spectra yields apattern of their energy distribution. Diagrams of cross-sections for γ-quanta formation were computed for the α-process elements. Synthetic γ-ray spectra of interstellar gasand dust were calculated individually and collectively. Ithas been indicated that, under certain conditions in AGN,cross-sections for ionisation of atoms due to energy lossesby cosmic-ray induced ionisation and γ-quanta emissionresulting from collisions with cosmic rays are similar. It hasbeen found that when the maximum of proton and α-particle energy distribution function falls within theinvestigated range of energies, it leads to the formation ofthe peak flux of γ-rays. This is particularly important forthe interpretation of observations in the energy ranges of 5-15 MeV and 23-30 MeV. Synthetic induced γ-ray spectraof interstellar dust were computed, and methods of theirobservations for silicate and carbon-containing dust, whichaccount for 80% and 20% of the interstellar-dust total mass,respectively, were determined. It has been deduced that thecontribution of Compton processes to γ-quanta emissioncan be neglected at the investigated energies.

CMB Shadows: The Effect of Interstellar Extinction on Cosmic Microwave Background Polarization and Temperature Anisotropy

Abstract We evaluate the degradation of the accuracy of the component separation between the cosmic microwave background (CMB) and foreground components caused by neglect of absorption of the CMB’s monopole component by the galactic interstellar matter. The amplitude of the temperature anisotropy caused by the CMB shadow, due to dust components, is about 1 μK. This value is comparable to the required noise level necessary to probe non-Gaussianity studies with upcoming CMB experiments. In addition, the amplitude of the polarization caused by the CMB shadow due to dust is comparable to or larger than the rms value of the CMB B-mode polarization, imprinted by primordial gravitational waves. We show that applying a single-power-law model as the dust spectrum to observed multifrequency data introduces systematic errors, which are comparable to or larger than the required noise level for forthcoming CMB B-mode polarization experiments. Deducing the intrinsic spectrum of dust emission from the submillimeter wave band data reduces the systematic error to below the required noise level. However, this method requires dust temperature measurements with an accuracy of better than a few percent. We conclude that the CMB shadow due to dust must be considered in future CMB missions for achieving their targeted sensitivity. Our results will be important to detect the primordial CMB B-mode polarization, with the amplitude of the tensor-to-scalar ratio of r = 10−3.

Confirmation of Enhanced Long-wavelength Dust Emission in OMC 2/3

Abstract Previous continuum observations from the MUSTANG camera on the Green Bank Telescope (GBT) of the nearby star-forming filament OMC 2/3 found elevated emission at 3.3 mm relative to shorter-wavelength data. As a consequence, the inferred dust emissivity index obtained from modified blackbody dust spectra was considerably lower than what is typically measured on ∼0.1 pc scales in nearby molecular clouds. Here we present new observations of OMC 2/3 collected with the MUSTANG-2 camera on the GBT that confirm this elevated emission. We also present for the first time sensitive 1 cm observations made with the Ka-band receiver on the GBT, which also show higher than expected emission. We use these observations—along with Herschel, JCMT, Mambo, and GISMO data—to assemble spectral energy distributions (SEDs) of a variety of structures in OMC 2/3 spanning the range 160 μm to 1 cm. The data at 2 mm and shorter are generally consistent with a modified blackbody spectrum and a single value of β ∼ 1.6. The 3 mm and 1 cm data, however, lie well above such an SED. The spectrum of the long-wavelength excess is inconsistent with both free–free emission and standard “Spinning Dust” models for Anomalous Microwave Emission (AME). The 3 mm and 1 cm data could be explained by a flatter dust emissivity at wavelengths shorter than 2 mm, potentially in concert with AME in some regions.

ALMA uncovers the [C ii] emission and warm dust continuum in a z = 8.31 Lyman break galaxy

ABSTRACT We report on the detection of the [C ii] 157.7 μm emission from the Lyman break galaxy (LBG) MACS0416_Y1 at z = 8.3113, by using the Atacama Large Millimeter/submillimeter Array (ALMA). The luminosity ratio of [O iii] 88 μm (from previous campaigns) to [C ii] is 9.3 ± 2.6, indicative of hard interstellar radiation fields and/or a low covering fraction of photodissociation regions. The emission of [C ii] is cospatial to the 850 μm dust emission (90 μm rest frame, from previous campaigns), however the peak [C ii] emission does not agree with the peak [O iii] emission, suggesting that the lines originate from different conditions in the interstellar medium. We fail to detect continuum emission at 1.5 mm (160 μm rest frame) down to 18 μJy (3σ). This non-detection places a strong limits on the dust spectrum, considering the 137 ± 26 μJy continuum emission at 850 μm. This suggests an unusually warm dust component (T > 80 K, 90 per cent confidence limit), and/or a steep dust-emissivity index (βdust > 2), compared to galaxy-wide dust emission found at lower redshifts (typically T ∼ 30–50 K, βdust ∼ 1–2). If such temperatures are common, this would reduce the required dust mass and relax the dust production problem at the highest redshifts. We therefore warn against the use of only single-wavelength information to derive physical properties, recommend a more thorough examination of dust temperatures in the early Universe, and stress the need for instrumentation that probes the peak of warm dust in the Epoch of Reionization.

Analysing the spectral energy distributions of Galactic classical Cepheids

Spectral energy distributions (SEDs) were constructed for a sample of 477 classical Cepheids (CCs); including stars that have been classified in the literature as such but are probably not. The SEDs were fitted with a dust radiative transfer code. Four stars showed a large mid- or far-infrared excess and the fitting then included a dust component. These comprise the well-known case of RS Pup, and three stars that are (likely) Type-II Cepheids (T2Cs), AU Peg, QQ Per, and FQ Lac. The infrared excess in FQ Lac is reported for the first time in this work. The remainder of the sample was fitted with a stellar photosphere to derive the best-fitting luminosity and effective temperature. Distance and reddening were taken from the literature. The stars were plotted in a Hertzsprung-Russell diagram (HRD) and compared to evolutionary tracks for Cepheids and theoretical instability strips. For the large majority of stars, the position in the HRD is consistent with the instability strip for a CC or T2C. About 5% of the stars are outliers in the sense that they are much hotter or cooler than expected. A comparison to effective temperatures derived from spectroscopy suggests in some cases that the photometrically derived temperature is not correct and that this is likely linked to an incorrectly adopted reddening. Two three-dimensional reddening models have been used to derive alternative estimates of the reddening for the sample. There are significant systematic differences between the two estimates with a non-negligible scatter. In this work the presence of a small near-infrared (NIR) excess, as has been proposed in the literature for a few well-known Cepheids, is investigated. Firstly, this was done by using a sample of about a dozen stars for which a mid-infrared spectrum is available. This data is particularly constraining as the shape of the observed spectrum should match that of the photosphere and any dust spectrum, both dust continuum and any spectral features of, for example, silicates or aluminium oxide. This comparison provides constraints on the dust composition, in agreement with a previous work in the literature. Secondly, the SEDs of all stars were fitted with a dust model to see if a statistically significant better fit could be obtained. The results were compared to recent work. Eight new candidates for exhibiting a NIR excess are proposed, solely based on the photometric SEDs. Obtaining mid-infrared spectra would be needed to confirm this excess. Finally, period-bolometric luminosity and period-radius relations are presented for samples of over 370 fundamental-mode CCs.

Spatial power spectra of dust across the Local Group: No constraint on disc scale height

ABSTRACT We analyse the 1D spatial power spectra of dust surface density and mid to far-infrared emission at $24\!-\!500\, \mu$m in the LMC, SMC, M31, and M33. By forward-modelling the point spread function (PSF) on the power spectrum, we find that nearly all power spectra have a single power-law and point source component. A broken power-law model is only favoured for the LMC 24 μm MIPS power spectrum and is due to intense dust heating in 30 Doradus. We also test for local power spectrum variations by splitting the LMC and SMC maps into 820 pc boxes. We find significant variations in the power-law index with no strong evidence for breaks. The lack of a ubiquitous break suggests that the spatial power spectrum does not constrain the disc scale height. This contradicts claims of a break where the turbulent motion changes from 3D to 2D. The power spectrum indices in the LMC, SMC, and M31 are similar (2.0–2.5). M33 has a flatter power spectrum (1.3), similar to more distant spiral galaxies with a centrally-concentrated H2 distribution. We compare the power spectra of H i, CO, and dust in M31 and M33, and find that H i power spectra are consistently flatter than CO power spectra. These results cast doubt on the idea that the spatial power spectrum traces large scale turbulent motion in nearby galaxies. Instead, we find that the spatial power spectrum is influenced by (1) the PSF on scales below ∼3 times the FWHM, (2) bright compact regions (30 Doradus), and (3) the global morphology of the tracer (an exponential CO disc).

SpitzerSpace Telescope observations of bilobate comet 8P/Tuttle

Context.Comet 8P/Tuttle is a nearly isotropic comet whose physical properties are poorly known and might be different from those of ecliptic comets owing to their different origin. Two independent observations have shown that 8P/Tuttle has a bilobate nucleus.Aims.Our goal is to determine the physical properties of the nucleus (size, shape, thermal inertia, and albedo) and coma (water and dust) of 8P/Tuttle.Methods.We observed the inner coma of 8P/Tuttle with the infrared spectrograph and the infrared camera of theSpitzerSpace Telescope. We obtained one spectrum (5–40μm) on 2 November 2007 and a set of 19 images at 24μm on 22–23 June 2008 sampling the rotational period of the nucleus. The data were interpreted using thermal models for the nucleus and the dust coma, and we considered two possible shape models of the nucleus derived fromHubbleSpace Telescope visible and Arecibo radar observations.Results.We favor a model for the nucleus shape that is composed of two contact spheres with respective radii of 2.7 ± 0.1 km and 1.1 ± 0.1 km and a pole orientation with RA = 285 ± 12° and Dec = +20 ± 5°. The thermal inertia of the nucleus lies in the range 0–100 J K−1m−2s−1∕2and theR-band geometric albedo is 0.042 ± 0.008. The water production rate amounts to 1.1 ± 0.2 × 1028molecules s−1at 1.6 AU from the Sun pre-perihelion, which corresponds to an active fraction of ≈9%. At the same distance, theɛfρquantity amounts to 310 ± 34 cm, and it reaches 325 ± 36 cm at 2.2 AU post-perihelion. The dust grain temperature is estimated to be 258 ± 10 K, which is 37 K higher than the thermal equilibrium temperature at 1.6 AU. This indicates that the dust grains that contribute to the thermal infrared flux have a typical size of ≈10μm. The dust spectrum exhibits broad emission around 10μm (1.5σconfidence level) and 18μm (5σconfidence level) that we attribute to amorphous pyroxene.

Link between E–B polarization modes and gas column density from interstellar dust emission

Context. The analysis of the Planck polarization E and B mode power spectra of interstellar dust emission at 353 GHz recently raised new questions concerning the impact of Galactic foregrounds on the detection of the polarization of the cosmic microwave background (CMB) and on the physical properties of the interstellar medium (ISM). In the diffuse ISM at high latitude a clear E–B asymmetry is observed that has twice as much power in E modes as in B modes; there is also a positive correlation between the total power, T, and both E and B modes, which is currently interpreted in terms of the link between the structure of interstellar matter and that of the Galactic magnetic field. Aims. In this paper we aim to extend the Planck analysis of the high latitude sky to low Galactic latitudes, investigating the correlation between the T–E–B auto- and cross-correlation power spectra with the gas column density from the diffuse ISM to molecular clouds. Methods. We divided the sky between Galactic latitudes |b| > 5° and |b| < 60° in 552 circular patches, with an area of ~400°2, and we studied the cross-correlations between the T–E–B power spectra and the column density of each patch using the latest release of the Planck polarization data. Results. We find that the B-to-E power ratio (DlBB/DlEE) and the TE correlation ratio (rTE) depend on column density. While the former increases going from the diffuse ISM to molecular clouds in the Gould Belt, the latter decreases. This systematic variation must be related to actual changes in ISM properties. The data show significant scatter about this mean trend. The variations of DlBB/DlEE and rTE are observed to be anticorrelated for all column densities. In the diffuse ISM, the variance of these two ratios is consistent with a stochastic non-Gaussian model in which the values of DlBB/DlEE and rTE are fixed. We finally discuss the dependences of TB and EB with column density, which are however hampered by instrumental noise. Conclusions. For the first time, this work shows significant variations of the T–E–B power spectra of dust polarized emission across a large portion of the Galaxy. Their dependence on multipole and gas column density is key for accurate forecasts of next generation CMB experiments and for constraining present models of ISM physics (i.e., dust properties and interstellar turbulence), which are considered responsible for the observed T–E–B signals.

Quantitative Detection of Dust Storms with the Millimeter Wave Radar in the Taklimakan Desert

In order to conduct real-time quantitative monitoring of dust storms, Ka-band millimeter wave radar (MMWR) was utilized for the consecutive detection of dust storms over the Taklimakan Desert from April to June 2018. The retrievals of the reflectivity factor, dust spectrum distribution and dust mass concentration were carried out with the power spectrum data detected by MMWR for three dust storm processes. The analysis shows that: The probability density distribution of dust conforms to the lognormal distribution. During the dust storm processes, the effective detection height of the reflectivity factor was within 2000 m and the range of the reflectivity factors was between-25 dBZ and 25 dBZ. During the floating dust period, the effective height of the dust spectrum distribution was lower than 300 m and the values of dust mass concentration were less than 31.62 μg·m-3,at a height of 200 m. Furthermore, during the blowing sand stage, the effective height of the dust spectrum distribution was normally lower than 600 m and the values of dust mass concentration were mainly less than 316.23 μg·m-3,at a height of 200 m. During the dust storm period, the effective height of the dust spectrum distributionexceeded1000 m; when the height was 100 m, the values of dust mass concentration were between 1220 μg∙m-3 and 42,146 μg∙m-3 and the average mass concentration was 9287 μg·m-3; whereas, the values of dust mass concentration were between 2 μg∙m-3 and 820 μg∙m-3 when the height was 1200m and the average mass concentration was 24 μg∙m-3. The relationship between the reflectivity factor Z and the dust mass concentration M isdefined as Z=651.6M0.796. Compared with the observational data from Grimm180 particle detector, the data of the retrieved dust mass concentration are basically accurate and this retrieved method proves to be feasible. Thus, the MMWR cans be used as a new device for quantitative monitoring of dust storms.

A study on the FTIR spectra of pre- and post-explosion coal dust to evaluate the effect of functional groups on dust explosion

Fourier transform infrared (FTIR) spectra of coal dust and its explosion solid residues were studied. Coal dust explosion test was carried out on a 20-L explosion device, and the variation of different functional groups and FTIR structural parameters of pre- and post-explosion dust were semi-quantitatively analyzed by deconvolution of the FTIR spectra. In addition, the relationship of explosion pressure (Pm) and pressure rise rate ((dP/dt)m) with functional groups was investigated. The results show that the largest consumption of functional groups in coal dust explosion process is distributed in 1800–1000cm−1 band, and most of the ether oxygen bond, methyl and benzene ring are removed from the coal macromolecule. The improved condensation degree of coal macromolecular aromatic ring and the decreased aliphatic side chains lead to a more compact coal molecular structure. The consumption of functional groups during coal dust explosion is positively correlated with the Pm and (dP/dt)m. The research provides a new feasible method for the evaluation of the organic dust explosion risk by its functional group. Moreover, it can be used effectively as basis for suppressing the organic dust explosion.