Dust Chemistry Research Articles

Chromatically modeling the parsec-scale dusty structure in the center of NGC 1068

Context. The Very Large Telescope Interferometer (VLTI) has been providing breakthrough images of the dust in the central parsecs of active galactic nuclei (AGNs), which is thought to be a key component of the AGN unification scheme and AGN host galaxy interaction. In single infrared bands, these images can enjoin multiple interpretations, some of which could challenge the unification scheme. This is the case for the archetypal type 2 AGN of NGC 1068, whereby the degeneracy is reduced by multi-band temperature maps that are hindered by an ambiguity in the alignment between different single-band images. Aims. We aim to solve this problem by creating a chromatic model capable of simultaneously explaining the VLTI GRAVITY+MATISSE 2 μm–13 μm observations of AGNs hosted by NGC 1068. Methods. We employed a simple disk and wind geometry populated by spherical black-body emitters and dust obscuration to create a versatile multi-wavelength modelling method for chromatic IR interferometric data of dusty objects. Results. This simple geometry is capable of reproducing the spectro-interferometric data of NGC 1068 from the K through N bands. It explains the complex single band images with obscuration and inclination effects, and it solves the alignment problem between bands. We find that the resulting model disk and wind geometry is consistent with previous studies of comparable and larger scales. For example, compared to molecular gas emission, our model wind position angle (PA) of 2322° is close to the mas-scale outflowing CO(6–5) PA of ∼33° seen with ALMA. The equivalent 90° offset model disk PA is also consistent with the CO(6–5) disk axis of 112° as well as the mas-scale disk axis from CO(2–1), CO(3–2), and HCO+(4–3) of 115 ± 5°. Furthermore, the resulting model images visually resemble the multiple achromatic image reconstructions of the same data when evaluated at the same wavelengths. We conclude that the IR emitting structure surrounding the AGN within NGC 1068 can indeed be explained by the clumpy disk+wind iteration of the AGN unification scheme. Within the scheme, we find that it is best explained as a type 2 AGN and the obscuring dust chemistry can be explained by a mix of olivine silicates and 16 ± 1% amorphous carbon.

Temperature stratification in a molecular shock: Analysis of the emission of H2 pure rotational lines in IC443G

Context. Supernovae remnants (SNRs) represent a major source of feedback from stars on the interstellar medium of galaxies. During the latest stage of supernova explosions (which lasts 10–100 kyr), shock waves produced by the initial blast modify the chemistry of gas and dust, inject kinetic energy in the surroundings, and may alter star formation characteristics. Simultaneously, γ-ray emission is generated by the interaction between the ambient medium and cosmic rays, in particular those locally accelerated in the early stages of the explosion. Aims. We aim to estimate the total molecular mass, local density, and total column density of H2 and the temperature structure in a shocked clump interacting with the supernova remnant IC443 located in a region where cosmic rays interact with the interstellar medium. Measuring the mass of the dense and neutral component of the medium is a prerequisite to understanding the chemistry, energetics, and GeV to TeV γ-ray emission. Methods. Assuming that the emission of H2 pure rotational lines is produced by a collection of gas layers with variable temperature, we compared Spitzer/IRS emission maps for the ν = 0–0 S(0) to S(7) lines with a thermal admixture model. Our description is based on a power-law distribution of thermalized components with temperatures varying between Tmin = 25 K and Tmax = 1500 K. Results. Our thermal admixture model allows the level populations of H2 to be described by a power-law distribution dN = ΛT−ΓdT, with Γ ~ 2.2−4.7. We measured a total mass MH2 = 220−80+110 M⊙ across the Spitzer/IRS field of observations. Conclusions. Our analysis shows that an estimate of the cold molecular gas temperature is paramount to accurately constraining the H2 mass, although the mass remains affected by significant uncertainties due to the assumptions on the gas temperature distribution.

Little evolution of dust emissivity in bright infrared galaxies from 2 < z < 6

ABSTRACT Variations in the dust emissivity index, $\beta$, within and between galaxies, are evidence that the chemistry and physics of dust must vary on large scales, although the nature of the physical and/or chemical variations is still unknown. In this paper, we estimate values of $\beta$ and dust temperature for a sample of 109 dusty star-forming galaxies (DSFGs) over the range, $2 \ \lt\ z \ \lt\ 6$. We compare the results obtained with both an optically thin model and a general opacity model, finding that our estimates of $\beta$ are similar between the models but our estimates of dust temperature are not. We find no evidence of a change in $\beta$ with redshift, with a median value of $\beta = 1.96$ for the optically thin model with a confidence interval (16–84 per cent) of 1.67 to 2.35 for the population. Using simulations, we estimate the measurement errors from our procedure and show that the variation of $\beta$ in the population results from intrinsic variations in the properties of the dust in DSFGs. At a fixed far-infrared luminosity, we find no evidence for a change in dust temperature, $T_{\textrm {dust}}$, with redshift. After allowing for the effects of correlated measurement errors, we find an inverse correlation between $\beta$ and $T_{\textrm {dust}}$ in DSFGs, for which there is also evidence in low-redshift galaxies.

Whither or Wither the Sulfur Anomaly in Planetary Nebulae?

We present a thorough investigation of the long-standing sulfur anomaly enigma. Our analysis uses chemical abundances from the most extensive data set available for 126 planetary nebulae (PNs) with improved accuracy and reduced uncertainties from a 10° × 10° Galactic bulge region. By using argon as a superior PN metallicity indicator, the anomaly is significantly reduced and better constrained. For the first time in PNs we show sulfur α-element lockstep with both oxygen and argon. We dispel hypotheses that the anomaly originates from underestimation of higher sulfur ionization stages. Using a machine-learning approach, we show that earlier ionization correction factor schemes contributed significantly to the anomaly. We find a correlation between the sulfur anomaly and the age/mass of PN progenitors, with the anomaly either absent or significantly reduced in PNs with young progenitors. Despite inherent challenges and uncertainties, we link this to PN dust chemistry, noting those with carbon-dust chemistry show a more pronounced anomaly. By integrating these findings, we provide a plausible explanation for the residual, reduced sulfur anomaly and propose its potential as an indicator of relative galaxy age compositions based on PNs.

Constraining the halo-ISM connection through multi-transition carbon monoxide line-intensity mapping

Line-intensity mapping (LIM) surveys will characterise the cosmological large-scale structure of emissivity in a range of atomic and molecular spectral lines, but existing literature rarely considers whether these surveys can recover excitation properties of the tracer gas species, such as the carbon monoxide (CO) molecule. Combining basic empirical and physical assumptions with the off-the-shelf Radex radiative transfer code or a Gaussian process emulator of Radex outputs, we devise a basic dark matter halo model for CO emission by tying bulk CO properties to halo properties, exposing physical variables governing CO excitation as free parameters. The CO Mapping Array Project (COMAP) is working towards a multi-band survey programme to observe both CO(1–0) and CO(2–1) at z ∼ 7. We show that this programme, as well as a further `Triple Deluxe' extension to higher frequencies covering CO(3–2), is fundamentally capable of successfully recovering the connection between halo mass and CO abundances, and constraining the molecular gas kinetic temperature and density within the star-forming interstellar medium in ways that single-transition CO LIM cannot. Given a fiducial thermal pressure of ∼ 104 K cm-3 for molecular gas in halos of ∼ 1010 M ⊙, simulated multi-band COMAP surveys successfully recover the thermal pressure within 68% interval half-widths of 0.5–0.6 dex. Construction of multi-frequency LIM instrumentation to access multiple CO transitions is crucial in harnessing this capability, as part of a cosmic statistical probe of gas metallicity, dust chemistry, and other physical parameters in star-forming regions of the first galaxies and proto-galaxies out of reionisation.

Probing the Nature of the First Galaxies with JWST and ALMA

By implementing a model of primordial dust emission, we predict dust-continuum fluxes for massive galaxy sources similar to those recently detected by James Webb Space Telescope (JWST) at z ≳ 7. Current upper flux limits, obtained with Atacama Large Millimeter/submillimeter Array (ALMA) for some of these sources, can constrain the gas metallicity and dust fraction of the first galaxies. Encouragingly, if assuming expected properties for typical first galaxies (i.e., dust-to-metal mass ratio: D/M = 5 × 10−3, gas metallicity: Z g = 5 × 10−3 Z ☉, star formation efficiency: η = 0.01), model far-infrared (FIR) fluxes are consistent with current upper flux limits inferred from ALMA bands 6 and 7 (≲104 nJy). Such low D/M values and metallicities are in agreement with some scenarios proposed in the literature to explain the nondetection of the FIR dust continuum for high-z JWST galaxy candidates. On the other hand, higher values of model parameters D/M (≳0.06) and Z g (≳5 × 10−2 Z ☉) are ruled out by observational data, unless a higher η is assumed. According to our findings, ALMA multiband observations could constrain the dust chemistry and dust grain size distribution in the early universe. In this context, future observational challenges would involve not only reaching higher FIR sensitivities, but also increasing the wavelength coverage by exploring distinct ALMA bands.

Impact of flow velocity on the heterogeneous reaction of SO2 over Fe2O3

Flow velocity, potentially linked to dry deposition velocity and wind speed parameters, show non-marginal significance in the heterogeneous oxidation of SO2 on α-Fe2O3 particles. Our uptake measurement results produce lab-based evidence that an increase in flow velocity can potentially strengthen SO2 uptake capability over α-Fe2O3 by nearly one order of magnitude within the range of considered reaction conditions. Additionally, specimen analysis of surface S-containing products indicates a distinct SO2 oxidation regime, shifting from the heterogeneous reaction mediated by active sites under low flow velocity and low RH to an aqueous-like multiphase-dominated pathway under high flow velocity and high RH. An attempt was further made to link this experimental parameter to dry deposition velocity regulated by wind force in the atmosphere. This work highlights the significance of flow velocity in triggering fast sulfate production concerning dust chemistry.

Carbon Abundance of Stars in the LAMOST-Kepler Field

The correlation between host star iron abundance and the exoplanet occurrence rate is well established and arrived at in several studies. Similar correlations may be present for the most abundant elements, such as carbon and oxygen, which also control the dust chemistry of the protoplanetary disk. In this paper, using a large number of stars in the Kepler field observed by the LAMOST survey, it has been possible to estimate the planet occurrence rate with respect to the host star carbon abundance. Carbon abundances are derived using synthetic spectra fit of the CH- G-band region in the LAMOST spectra. The carbon abundance trend with metallicity is consistent with the previous studies and follows the Galactic chemical evolution (GCE). Similar to [Fe/H], we find that the [C/H] values are higher among giant-planet hosts. The trend between [C/Fe] and [Fe/H] in planet hosts and single stars is similar; however, there is a preference for giant planets around host stars with a subsolar [C/Fe] ratio and higher [Fe/H]. Higher metallicity and subsolar [C/Fe] values are found among younger stars as a result of GCE. Hence, based on the current sample, it is difficult to interpret the results as a consequence of GCE or due to planet formation.

A Methodological Review of Tools That Assess Dust Microbiomes, Metatranscriptomes and the Particulate Chemistry of Indoor Dust

Indoor house dust is a blend of organic and inorganic materials, upon which diverse microbial communities such as viruses, bacteria and fungi reside. Adequate moisture in the indoor environment helps microbial communities multiply fast. The outdoor air and materials that are brought into the buildings by airflow, sandstorms, animals pets and house occupants endow the indoor dust particles with extra features that impact human health. Assessment of the health effects of indoor dust particles, the type of indoor microbial inoculants and the secreted enzymes by indoor insects as allergens merit detailed investigation. Here, we discuss the applications of next generation sequencing (NGS) technology which is used to assess microbial diversity and abundance of the indoor dust environments. Likewise, the applications of NGS are discussed to monitor the gene expression profiles of indoor human occupants or their surrogate cellular models when exposed to aqueous solution of collected indoor dust samples. We also highlight the detection methods of dust allergens and analytical procedures that quantify the chemical nature of indoor particulate matter with a potential impact on human health. Our review is thus unique in advocating the applications of interdisciplinary approaches that comprehensively assess the health effects due to bad air quality in built environments.

Enhanced Deposition of Atmospheric Soluble Iron by Intrusions of Marine Air Masses to East Antarctica

AbstractBio‐essential iron can relieve nutrient limitation and stimulate marine productivity in the Southern Ocean. The fractional iron solubility of aerosol iron is an important variable determining iron availability for biological uptake. However, estimates of dissolved iron (dFe; iron < 0.2 μm) and the factors driving the variability of fractional iron solubility in pristine air masses are largely unquantified. To constrain inputs of fractional iron solubility to remote East Antarctic waters, dFe, total dissolvable iron (TDFe), trace elements and refractory black carbon were analyzed in a 9‐year‐old snow pit (2005–2014) from a new ice core site at Aurora Basin North (ABN) in Wilkes Land, East Antarctica. Extremely low annual dFe deposition fluxes were estimated (0.2 × 10−6 g m−2 y−1), while annual TDFe deposition fluxes (70 × 10−6 g m−2 y−1) were comparable to other Antarctic sites. TDFe is dominantly sourced from mineral dust. Unlike coastal Antarctic sites where the variability of fractional iron solubility in modern snow is explained by a mixture of dust and biomass burning sources, dFe deposition and fractional iron solubility at ABN (ranging between 0.1% and 6%) is enhanced in episodic high precipitation events from synoptic warm air masses. Enhanced fractional iron solubility reaching the high elevation site at ABN is suggested through the mechanism of cloud processing of background mineral dust that modifies the dust chemistry and increases iron dissolution during long‐range transport. This study highlights a complex interplay of sources and processes that drive fractional iron solubility in pristine air masses.

Chemistry and particle size distribution of respirable coal dust in underground mines in Central Eastern Europe

Despite international efforts to limit worker exposure to coal dust, it continues to impact the health of thousands of miners across Europe. Airborne coal dust has been studied to improve risk models and its control to protect workers. Particle size distribution analyses shows that using spraying systems to suppress airborne dusts can reduce particulate matter concentrations and that coals with higher ash yields produce finer dust. There are marked chemical differences between parent coals and relatively coarse deposited dusts (up to 500 µm, DD500). Enrichments in Ca, K, Ba, Se, Pb, Cr, Mo, Ni and especially As, Sn, Cu, Zn and Sb in the finest respirable dust fractions could originate from: (i) mechanical machinery wear; (ii) variations in coal mineralogy; (iii) coal fly ash used in shotcrete, and carbonates used to reduce the risk of explosions. Unusual enrichments in Ca in mine dusts are attributed to the use of such concrete, and elevated K to raised levels of phyllosilicate mineral matter. Sulphur concentrations are higher in the parent coal than in the DD500, probably due to relatively lower levels of organic matter. Mass concentrations of all elements observed in this study remained below occupational exposure limits.

Impact of metals on (star)dust chemistry: a laboratory astrophysics approach.

Laboratory experiments are essential in exploring the mechanisms involved in stardust formation. One key question is how a metal is incorporated into dust for an environment rich in elements involved in stardust formation (C, H, O, Si). To address experimentally this question we have used a radiofrequency cold plasma reactor in which cyclic organosilicon dust formation is observed. Metallic (silver) atoms were injected in the plasma during the dust nucleation phase to study their incorporation in the dust. The experiments show formation of silver nanoparticles (~15 nm) under conditions in which organosilicon dust of size 200 nm or less is grown. The presence of AgSiO bonds, revealed by infrared spectroscopy, suggests the presence of junctions between the metallic nanoparticles and the organosilicon dust. Even after annealing we could not conclude on the formation of silver silicates, emphasizing that most of silver is included in the metallic nanoparticles. The molecular analysis performed by laser mass spectrometry exhibits a complex chemistry leading to a variety of molecules including large hydrocarbons and organometallic species. In order to gain insights into the involved chemical molecular pathways, the reactivity of silver atoms/ions with acetylene was studied in a laser vaporization source. Key organometallic species, Ag n C2H m (n=1-3; m=0-2), were identified and their structures and energetic data computed using density functional theory. This allows us to propose that molecular Ag-C seeds promote the formation of Ag clusters but also catalyze hydrocarbon growth. Throughout the article, we show how the developed methodology can be used to characterize the incorporation of metal atoms both in the molecular and dust phases. The presence of silver species in the plasma was motivated by objectives finding their application in other research fields than astrochemistry. Still, the reported methodology is a demonstration laying down the ground for future studies on metals of astrophysical interest such as iron.

Vernon Morris has uncovered the secret chemistry of atmospheric dust

Vernon Morris has uncovered the secret chemistry of atmospheric dust

Interstellar anatomy of the TeV gamma-ray peak in the IC443 supernova remnant

Context.Supernova remnants (SNRs) represent a major feedback source from stars in the interstellar medium of galaxies. During the latest stage of supernova explosions, shock waves produced by the initial blast modify the chemistry of gas and dust, inject kinetic energy into the surroundings, and may alter star formation characteristics. Simultaneously,γ-ray emission is generated by the interaction between the ambient medium and cosmic rays (CRs), including those accelerated in the early stages of the explosion.Aims.We study the stellar and interstellar contents of IC443, an evolved shell-type SNR at a distance of 1.9 kpc with an estimated age of 30 kyr. We aim to measure the mass of the gas and characterize the nature of infrared point sources within the extended G region, which corresponds to the peak ofγ-ray emission detected by VERITAS andFermi.Methods.We performed 10′ × 10′ mapped observations of12CO,13COJ= 1–0,J= 2–1, andJ= 3–2 pure rotational lines, as well as C18OJ= 1–0 andJ= 2–1 obtained with the IRAM 30 m and APEX telescopes over the extent of theγ-ray peak to reveal the molecular structure of the region. We first compared our data with local thermodynamic equilibrium models. We estimated the optical depth of each line from the emission of the isotopologs13CO and C18O. We used the population diagram and large velocity gradient assumption to measure the column density, mass, and kinetic temperature of the gas using12CO and13CO lines. We used complementary data (stars, gas, and dust at multiple wavelengths) and infrared point source catalogs to search for protostar candidates.Results.Our observations reveal four molecular structures: a shocked molecular clump associated with emission lines extending between −31 and 16 km s−1, a quiescent, dark cloudlet associated with a line width of ~2 km s−1, a narrow ring-like structure associated with a line width of ~1.5 km s−1, and a shocked knot. We measured a total mass of ~230, ~90, ~210, and ~4M⊙, respectively, for the cloudlet, ring-like structure, shocked clump, and shocked knot. We measured a mass of ~1100M⊙throughout the rest of the field of observations where an ambient cloud is detected. We found 144 protostar candidates in the region.Conclusions.Our results emphasize how the mass associated with the ring-like structure and the cloudlet cannot be overlooked when quantifying the interaction of CRs with the dense local medium. Additionally, the presence of numerous possible protostars in the region might represent a fresh source of CRs, which must also be taken into account in the interpretation ofγ-ray observationsin this region.

Interstellar oxygen along the line of sight of Cygnus X-2

Interstellar dust permeates our Galaxy and plays an important role in many physical processes in the diffuse and dense regions of the interstellar medium (ISM). High-resolution X-ray spectroscopy, coupled with modelling based on laboratory dust measurements, provides a unique probe for investigating the interstellar dust properties along our line of sight towards Galactic X-ray sources. Here, we focus on the oxygen content of the ISM through its absorption features in the X-ray spectra. To model the dust features, we perform a laboratory experiment using the electron microscope facility located at the University of Cadiz in Spain, where we acquire new laboratory data in the oxygen K-edge. We study 18 dust samples of silicates and oxides with different chemical compositions. The laboratory measurements are adopted for our astronomical data analysis. We carry out a case study on the X-ray spectrum of the bright low-mass X-ray binary Cygnus X-2, observed by XMM−Newton. We determine different temperature phases of the ISM and parameterise oxygen in both gas (neutral and ionised) and dust form. We find Solar abundances of oxygen along the line of sight towards the source. Due to both the relatively low depletion of oxygen into dust form and the shape of the oxygen cross section profiles, it is challenging to determine the precise chemistry of interstellar dust. However, silicates provide an acceptable fit. Finally, we discuss the systematic discrepancies in the atomic (gaseous phase) data of the oxygen edge spectral region using different X-ray atomic databases as well as consider future prospects for studying the ISM with the Arcus concept mission.

Biogeochemistry of Household Dust Samples Collected from Private Homes of a Portuguese Industrial City

The main objectives of the present study were to (i) investigate the effects of mineralogy and solid-phase distribution on element bioaccessibility and (ii) perform a risk assessment to calculate the risks to human health via the ingestion pathway. Multiple discriminant analysis showed that the dust chemistry discriminates between indoor and outdoor samples. The solid-phase distribution of the elements in indoor dust indicated that a large proportion of zinc, nickel, lead, copper, and cobalt is associated with an aluminum oxy-hydroxides component, formed by the weathering of aluminum silicates. This component, which seems to influence the mobility of many trace elements, was identified for a group of indoor dust samples that probably had a considerable contribution from outdoor dust. An iron oxide component consisted of the highest percentage of chromium, arsenic, antimony, and tin, indicating low mobility for these elements. The bioaccessible fraction in the stomach phase from the unified BARGE method was generally high in zinc, cadmium, and lead and low in nickel, cobalt, copper, chromium, and antimony. Unlike other potentially toxic elements, copper and nickel associated with aluminum oxy-hydroxides and calcium carbonates were not extracted by the stomach solutions. These trace elements possibly form stable complexes with gastric fluid constituents such as pepsin and amino acid. Lead had a hazard quotient >1, which indicates the risk of non-carcinogenic health effects, especially for children.

Spatially resolving the chemical composition of the planet building blocks

ABSTRACT The inner regions of protoplanetary discs (from ∼0.1 to 10 au) are the expected birthplace of planets, especially telluric. In those high-temperature regions, solids can experience cyclical annealing, vapourisation, and recondensation. Hot and warm dusty grains emit mostly in the infrared domain, notably in N-band (8–13 μm). Studying their fine chemistry through mid-infrared spectro-interferometry with the new Very Large Telescope Interferometer (VLTI) instrument Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE), which can spatially resolve these regions, requires detailed dust chemistry models. Using radiative transfer, we derived infrared spectra of a fiducial static protoplanetary disc model with different inner-disc (<1 au) dust compositions. The latter were derived from condensation sequences computed at local thermodynamic equilibrium (LTE) for three initial C/O ratios: subsolar (C/O = 0.4), solar (C/O = 0.54), and supersolar (C/O = 1). The three scenarios return very different N-band spectra, especially when considering the presence of sub-micron-sized dust grains. MATISSE should be able to detect these differences and trace the associated sub-au-scale radial changes. We propose a first interpretation of N-band ‘inner-disc’ spectra obtained with the former VLTI instrument MID-infrared Interferometric instrument (MIDI) on three Herbig stars (HD 142527, HD 144432, HD 163296) and one T Tauri star (AS 209). Notably, we could associate a supersolar (‘carbon-rich’) composition for HD 142527 and a subsolar (‘oxygen-rich’) one for HD 1444432. We show that the inner-disc mineralogy can be very specific and not related to the dust composition derived from spatially unresolved mid-infrared spectroscopy. We highlight the need for including more complex chemistry when interpreting solid-state spectroscopic observations of the inner regions of discs, and for considering dynamical aspects for future studies.

Dust deposition tracks late-Holocene shifts in monsoon activity and the increasing role of human disturbance in the Puna-Altiplano, northwest Argentina

The Puna-Altiplano plateau represents a regionally significant dust source, which is critically located at the nexus between the tropical and sub-polar synoptic systems that dominate the South American climate. Dust emissions in this region would therefore be expected to be sensitive to changes in these systems, in particular the strength and position of the South American Summer Monsoon (SASM). Here, we present a late-Holocene multi-proxy study where changes in dust flux, reconstructed from a high-altitude peat mire, are examined in light of climate variability and human impacts. Results show that for most the 4300 cal. yr BP record, dust flux sensitively tracked changes in SASM activity. Prior to 2600 cal. yr BP relatively high dust flux implies dry conditions prevailed across the Puna-Altiplao in association with reduced SASM activity. The chemistry of dust deposited at this time matched the large endorheic basins on the Puna, which host ephemeral lakes and terminal fans, indicating these were actively supplying dust to the airstream. After 2600 cal. yr BP, SASM activity increased while dust flux decreased and the dust chemistry changed, collectively implying the shutting down of the Puna-Altiplano as a significant dust source. Dust flux increased after 1000 cal. yr BP during the ‘Medieval Warm Period’, associated with a return to drier conditions and reactivation of dust sources across the endorheic basins of the Puna. Natural variability in dust flux was dwarfed, however, by the very significant increase in flux after 400 cal. yr BP following Spanish Colonisation and associated changing landuse practices. This finding attests to the globally significant role of humans on dust emissions.

Investigation of soiling effects, dust chemistry and optimum cleaning schedule for PV modules in Lahore, Pakistan

We investigate the photovoltaic (PV) power losses due to soiling for Lahore, Pakistan for solar panels. Optimized cleaning schedules are proposed incorporating the effect of solar panels’ tilt angle and the method (manual vs. automatic) for cleaning. Output power losses and dust accumulation on solar panels were measured at variable tilt angles for a period of 120 days at an open roof top location in Lahore. The relative soiling losses for monofacial vs. bifacial (constructed by stacking two back to back monofacial) solar panels were compared for two different panel orientations, i.e., south faced tilted panels vs. East/West faced vertical panels. We found that the soiling rate for Lahore was consistently around 0.8% per day for 30° tilted panel (for the measurement period between October to January), which is among one of the highest soiling rates reported for various urban locations across South Asian and Gulf regions. A dust accumulation rate of 0.01−0.02mg/cm2 per day was recorded for panels that were fixed at 30° tilt. The variation for soiling/dust deposition rates was found to be negligible for different dry periods spanning between October and January. The chemistry and composition of the dust were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and, electron dispersive x-ray (EDX) spectroscopy. Large contents of carbon and quartz were found in the dust collected from the samples through EDX and XRD analysis. High carbon contents in the accumulated dust are attributed to air pollutants and could be a contributing factor for the high soiling rate. For manual cleaning, the optimal cleaning schedule was calculated to be about once per week for panels at 30° tilt, and, once every three weeks for panels at 90° tilt.

The morphological, elastic, and electric properties of dust aggregates in comets: A close look at COSIMA/Rosetta’s data on dust in comet 67P/Churyumov-Gerasimenko

The Cometary Secondary Ion Mass Analyzer (COSIMA) onboard ESA’s Rosetta orbiter has revealed that dust particles in the coma of comet 67P/Churyumov-Gerasimenko are aggregates of small grains. We study the morphological, elastic, and electric properties of dust aggregates in the coma of comet 67P/Churyumov-Gerasimenko using optical microscopic images taken by the COSIMA instrument. Dust aggregates in COSIMA images are well represented as fractals in harmony with morphological data from MIDAS (Micro-Imaging Dust Analysis System) and GIADA (Grain Impact Analyzer and Dust Accumulator) onboard Rosetta. COSIMA’s images, together with the data from the other Rosetta’s instruments such as MIDAS and GIADA do not contradict the so-called rainout growth of 10 ​μm-sized particles in the solar nebula. The elastic and electric properties of dust aggregates measured by COSIMA suggest that the surface chemistry of cometary dust is well represented as carbonaceous matter rather than silicates or ices, consistent with the mass spectra, and that organic matter is to some extent carbonized by solar radiation, as inferred from optical and infrared observations of various comets. Electrostatic lofting of cometary dust by intense electric fields at the terminator of its parent comet is unlikely, unless the surface chemistry of the dust changes from a dielectric to a conductor. Our findings are not in conflict with our current understanding of comet formation and evolution, which begin with the accumulation of condensates in the solar nebula and follow with the formation of a dust mantle in the inner solar system.