Mixing Of Dust Research Articles

Effect of Tire Buffings Addition on Compaction Properties of Bentonite-Sand, Bentonite-Rock Dust, and Bentonite-Sand-Rock Dust Mixes

Abstract: In landfills, the compacted bentonite-sand (B:S) combination is widely employed as a liner. Since sand is a scarce and expensive material, other waste materials such as rock dust which possess similar properties are used instead of sand, or in other cases, both sand and rock dust are mixed in varying proportions along with bentonite. Urbanization and population explosion have triggered the continuous increase in industrial waste output, particularly waste tires, which posed several challenges to mankind. Incorporating wastes tire as raw resources have been suggested in various industries. Waste tires as stabilizers and investigation of geotechnical properties of the composite can help to minimize pollution while also providing economic and scientific benefits. Past research indicates short fibre has been shown to improve the ductility, toughness, and resistance to tensile cracking of clays. Fibre-shaped tire buffings or tire dust (T) from the retreading process can be used as a fibre reinforcing element in a liner. The objective of this study is to examine the effect of fibre-shaped tire dust (T) addition on the compaction characteristics of bentonite-sand (B:S),bentonite-rock dust (B:R), and bentonite-sand-rock dust(B:S:R) mixes. Locally available sand and rock dust, and commercially available bentonite have been used in this research. The gradation of the (T) used is equivalent to poorly graded sand. Here, all the mixes were prepared with different (T) contents (2 to 16%), and the standard compaction tests were performed. The results reveal that when the tire dust increases, the variation in the optimum moisture content and maximum dry density follow a consistent and predictable pattern. To put it another way, with the increase in the percentage of tire dust in the combination, the optimum moisture content increases while the maximum dry density decreases. Additionally, relationships were offered to predict the maximum dry density and the optimum moisture content with various tire dust content of the composite to be functional in the field

Mixture Experiment Model for Predicting Static Modulus of Elasticity of Laterite-Quarry Dust Cement Block

Laterite-quarry dust cement block are masonry unit produce by full replacement of natural sand with appropriate mix of laterite and quarry dust. Static modulus of elasticity is an important parameter in predicting the structural behavior in service under load action and determines the deformations and displacements distribution concrete and similar other structural members like blocks. In this work, a mathematical model is formulated using Mixture experiment for predicting the static modulus of elasticity of laterite-quarry dust block. The model is tested for lack of fit and found adequate.

Development and evolution of an anomalous Asian dust event across Europe in March 2020

Abstract. This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over southern Europe in late March 2020 (27–30 March 2020). This event was associated with an anomalous circulation pattern leading to several days of PM10 (particulate matter with an aerodynamic diameter less than 10 µm) exceedances in connection with a dust source located in central Asia; this is a rare source of dust for Europe, which is more frequently affected by dust outbreaks from the Sahara Desert. The synoptic meteorological configuration was analyzed in detail, and the aerosol evolution during the transit of the dust plume over northern Italy was assessed at high time resolution by means of optical particle counting at three stations, namely Bologna, Trieste, and Mt. Cimone, allowing for the revelation of the transport timing among the three locations. Back-trajectory analyses supported by Copernicus Atmosphere Monitoring Service (CAMS) maps allowed for the location of the mineral dust source area in the Aralkum region. Therefore, the event was analyzed by observing the particle number size distribution with the support of chemical composition analysis. It is shown that the PM10 exceedance recorded is associated with a large fraction of coarse particles, which is in agreement with mineral dust properties. Both the in situ number size distribution and the vertical distribution of the dust plume were cross-checked using lidar ceilometer and aerosol optical depth (AOD) data from two nearby stations and showed that the dust plume (in contrast to those originating from the Sahara Desert) traveled close to the ground (up to a height of about 2 km). The limited mixing layer height caused by high concentrations of absorbing and scattering aerosols caused the mixing of mineral dust with other locally produced ambient aerosols, thereby potentially increasing its morbidity effects.

Expanding the Application Scope of Fine Dust from Petroleum Coke Calcining Furnaces in Aluminum Production

This paper discusses the formation and recycling of finely dispersed carbon dust that is captured by electric filters in petroleum coke calcination kilns. The paper analyzes the physical and chemical properties of such dust; it is a fine powder with a particle size of 60 μm and a density of 1.98 g/cm3; the ash content of the samples in this research was 0.97% on average, and the volatile yield was 1.45%. This waste could be of use in a variety of industries as a fuel; it could also be used as a reductant once pelletized. The paper proposes a pelletizing method using various binders: liquid glass, sodium lignosulfonate, carboxymethyl cellulose, cement, and dust produced by cleaning anode gases of electrolysis units. The method involves mixing carbon dust with the required amount of the binder and adding water to reach the required moisture content in the charge. The resulting charge is then to be pressed in a mold at up to 250 MPa. The research team studied how each of the binders affected the drop strength of the resulting pellets; the best results were obtained with a binder content of 5% to 6%; the drop resistance was best for liquid glass (85.0%), anode gas cleaning dust (75%), sodium lignosulfonate (94%), carboxymethyl cellulose (86%), and cement (93%).

Snow albedo reductions induced by the internal/external mixing of black carbon and mineral dust, and different snow grain shapes across northern China

Previous studies have indicated that black carbon (BC) potentially induces snow albedo reductions across northern China. However, the effects of other light-absorbing particles (LAPs, e.g., mineral dust, MD), snow grain shape, or BC–snow mixing state on snow albedo have been largely ignored. Here we evaluate the BC- and MD-induced snow albedo reductions and radiative forcings (RFs) using an updated Snow, Ice, and Aerosol Radiation radiative transfer model, considering all of the potential factors that can be derived from the field observations across northern China. The results highlight that the LAP-induced albedo reductions for nonspherical snow grains are 2%–30% less than those for spherical grains. Furthermore, BC–snow internal mixing can significantly enhance albedo reduction by a factor of 1.42–1.48 relative to external mixing, with snow grain radius ranging from 100 to 1000 μm. The mean regional BC + MD-induced snow albedo reductions are amplified by the increase of snow grain radius, ranging from 0.012 to 0.123 for fresh snow to 0.016–0.227 for old snow. Finally, we discuss the relative contributions of BC and MD to the albedo reductions and RFs, highlighting the dominant role of BC in reducing snow albedo across northern China.

Numerical study on the characteristics of a nano-aluminum dust-air jet flame

Nano-sized aluminum dust is quite attractive in the application scenarios with limited residence time. This study simulated an aluminum nanoparticle-air jet flame in a burner that was proposed to characterize the mixing and burning properties of dust and air in a classical ramjet configuration. The model considers the flow of gas phase by employing three-dimensional multicomponent Navier-Stokes equations, and the aluminum particles via the Lagrange approach. A combustion sub-model was developed to characterize the heat convection, radiation and combustion processes of nano-sized aluminum particles. Thereafter, the model was validated by comparing with experimental results of dust jet flow and aluminum particle combustion. With the present model, the characteristics of flow field, and variations of particle temperature, heat release and statuses etc. were examined in detail, by which the mixing zone and flame structure were defined. The results showed that the nano-aluminum particles in the inner mixing layer were firstly ignited by the hot co-flow air and burned, and these particles in the core jet region were ignited downstream. Once the aluminum particles were ignited, they burned out promptly in this burner. The effects of particle size were evaluated, and the results show that the lengths of mixing layer and reaction zone, as well as the width of reaction zone reduce with decreasing particle size, whereas the width of mixing layer stays the same.

Characteristics, sources and health risk assessment of PM2.5 in China's coal and coking heartland: Insights gained from the regional observations during the heating season

High emissions of particulate pollutants in a regional scale adversely affect global air quality, health welfare and climate change. The Fen-Wei Plain (FWP) of China is among the most polluted regions of China and worldwide due to its thriving coal and coking industry. However, the joint regional observations are scarce in the FWP of China. In this study, comprehensive measurements were performed in 11 FWP cities from November 15, 2019, to March 15, 2020 (the heating period). The results showed that the FWP experienced the severest PM2.5 (particulate matter with an aerodynamic diameter of 2.5 μm or less) pollution with an average concentration of 95.0 ± 52.4 μg/m3 despite the Chinese government's rolling out of a three-year action plan for clean air. Benefitted from desulfurization technologies, organic matter (OM) and nitrate became the most dominant contributors, accounting for averages of 28.3% and 22.2% of PM2.5, respectively. In addition to chemical conversion, as determined by the potential source contribution function analysis, atmospheric circulation within the FWP resulted in high concentrations of OM and NO3−. The major water-soluble ionic concentrations in PM2.5 were found in the order NO3− > SO42− > NH4+ > Cl− in the FWP. The observed elements accounted in total for 3.4% of the PM2.5 mass. For the spatial distribution of PM2.5-associated chemical species, OM ranged from 17.9 to 40.3 μg/m3, with the highest OM observed in Yuncheng. The proportions of NO3−/PM2.5 in the cities of Henan and Shaanxi Provinces were higher than those in Shanxi Province. Five or six kinds of PM2.5 sources were identified in the 11 FWP cities during the heating period including secondary sulfate and nitrate, vehicular exhaust, biomass burning and coal combustion or their mixing sources, industry and dust. The contribution of the secondary sulfate and nitrate comprised the largest source of PM2.5 (approximately 25.5%), while that of dust was the lowest (6.7%) in the FWP. The lifetime cancer risks in the 11 cities of the FWP from exposure to ambient PM2.5-bound elements ranged from 1.2 E−4 to 8.7 E−4, which were higher than the United States Environmental Protection Agency (U.S. EPA) acceptable level of 1 E−4; while the hazard quotients from exposure to ambient PM2.5-bound elements was more than 18, much higher than the U.S. EPA acceptable level of 1. This study provides insights on the heavy particulate pollution problem in highly polluted regions of China and up-to-date dataset to study climatic effect and health risk assessment caused by high PM loading.

Supervise the physicochemical quality of ground water using soft computing technique

ABSTRACT Water resources are essential for human beings and nowadays polluted water jeopardizes the human health. Toxic substances come from houses, industries and farm lands, dust mix with water causes water pollution. This pollution depreciates the quality of water and affects the human life. In this paper, our objective is to evaluate and supervise the physicochemical quality of the ground water, for the safety of human beings. The sample quality of 15 sites was used for measuring important parameters like pH, EC, Ca2+, Mg2+, Na+, K+, Cl−, SO42−, Also, NH4+ and NO3−, Fe2+ and HCO3−12 were considered for performance analysis. A soft computing component fuzzy logic system is used to design an intelligent system. The fuzzy logic system-based model measures groundwater quality status along with its sustainability. The results obtained from the model help the authorities, policy makers to plan proper policies for geochemical operation (water treatment process) and a foundation for observing the physicochemical quality of water in the area.

The GRAVITY young stellar object survey

Context. Protoplanetary disks drive some of the formation process (e.g., accretion, gas dissipation, formation of structures) of stars and planets. Understanding such physical processes is one of the most significant astrophysical questions. HD 163296 is an interesting young stellar object for which infrared and sub-millimeter observations have shown a prominent circumstellar disk with gaps plausibly created by forming planets. Aims. This study aims to characterize the morphology of the inner disk in HD 163296 with multi-epoch, near-infrared interferometric observations performed with GRAVITY at the Very Large Telescope Interferometer. Our goal is to depict the K-band (λ0 ~ 2.2 μm) structure of the inner rim with milliarcsecond (sub-au) angular resolution. Our data is complemented with archival Precision Integrated-Optics Near-infrared Imaging ExpeRiment (H-band; λ0 ~ 1.65 μm) data of the source. Methods. We performed a gradient descent parametric model fitting to recover the sub-au morphology of our source. Results. Our analysis shows the existence of an asymmetry in the disk surrounding the central star of HD 163296. We confirm variability of the disk structure in the inner ~2 mas (0.2 au). While variability of the inner disk structure in this source has been suggested by previous interferometric studies, this is the first time that it is confirmed in the H- and K-bands by using a complete analysis of the closure phases and squared visibilities over several epochs. Because of the separation from the star, position changes, and the persistence of this asymmetric structure on timescales of several years, we argue that it is probably a dusty feature (e.g., a vortex or dust clouds) made by a mixing of silicate and carbon dust and/or refractory grains, inhomogeneously distributed above the mid-plane of the disk.

Polarised emission from aligned dust grains in nearby galaxies: Predictions from the Auriga simulations

Context. Polarised emission from non-spherical dust grains contains information about the alignment of these dust grains and traces the structure of the interstellar magnetic field. Methods. We post-processed a set of Milky-Way-like galaxies from the Auriga project, assuming a dust mix consisting of spheroidal dust grains that are partially aligned with the model magnetic field. We constrained our dust model using Planck 353 GHz observations of the Milky Way. This model was then extrapolated to shorter wavelengths that cover the peak of interstellar dust emission and to observations of arbitrarily oriented nearby Milky-Way-like galaxies. Results. Assuming an intrinsic linear polarisation fraction that does not vary significantly with wavelength for wavelengths longer than 50 micron, we predict a linear polarisation fraction with a maximum of 10 − 15% and a median value of ≈7% for face-on galaxies and ≈3% for edge-on galaxies. The polarisation fraction anti-correlates with the line of sight density and with the angular dispersion function which expresses the large-scale order of the magnetic field perpendicular to the line of sight. The maximum linear polarisation fraction agrees well with the intrinsic properties of the dust model. The true magnetic field orientation can be traced along low density lines of sight when it is coherent along the line of sight. These results also hold for nearby galaxies, where a coherent magnetic field structure is recovered over a range of different broad bands. Conclusions. Polarised emission from non-spherical dust grains accurately traces the large-scale structure of the galactic magnetic field in Milky-Way-like galaxies, with expected maximum linear polarisation fractions of 10 − 15%. To resolve this maximum, a spatial resolution of at least 1 kpc is required.

STUDY ON UTILIZATION OF STONE DUST FOR STABILIZATION OF BLACK COTTON SOIL

Soil stabilization has become a major issue in construction engineering. Due to rapid growth of population and urbanization, there is tremendous increase in construction activities may lead to shortage of land for construction of buildings, roads, etc. The land available may not be suitable for construction activites. The soil may be black cotton, clayey, and loamy. This existing sites not suitable for construction because These soil has less bearing capacity and stability. The present experiment work briefly describes the suitability of local available Stone Dust(SD).The objective of this study to improvement of properties of soil by using of Stone Dust(SD) obtained from stone quarry.It will minimizethe environment harzord also.Different percentage of stone dust mix with black cotton soil. The effect of Stone Dust(SD) on Liquid Limit, Plastic Limit, Plasticity Index, Dry Density, Optimum Moisture Content (OMC) and California Bearing Ratio(CBR) values is tested in laboratory.

Desert and anthropogenic mixing dust deposition influences microbial communities in surface waters of the western Pacific Ocean

The western Pacific Ocean is particularly affected by dust aerosols due to the transport of desert-natural sand and industrially derived particulate matter with aerodynamic diameter < 2.5 μm (PM2.5) from continental Asia. Both oligotrophic and nutrient-sufficient surface water occurs in this region and these are speculated to support different microbial community dynamics. Here, we report evidence from four shipboard experiments in the western Pacific Ocean supplying oligotrophic and nutrient-sufficient surface waters with aerosol particles obtained from the nearby coastal mountains, to simulate dust and anthropogenic aerosol inputs in the ocean region. A sharp increase in nitrate for surface waters after addition of dust aerosols resulted in large increases in diatom abundance in oligotrophic waters, whilst in nutrient-sufficient waters the response of diatom population was reduced. The increase in organic matter provided by aerosol inputs and/or increase in phytoplankton biomass induced the growth of heterotrophic prokaryotes, such as Rhodobacteraceae and Alteromonadaceae populations, in both oligotrophic and nutrient-sufficient seawater. Anthropogenic and desert-natural dust is an important source of nitrate and organics to oceanic waters and such inputs can directly affect primary production and heterotrophic prokaryotic abundance in the ocean, implying consequences for the carbon cycle in these aerosol-affected waters.

Microstructural Analyses of Cement-Based Binders in Stabilizing Champlain Sea Clay

This research investigated the strength development and the microstructural change in Champlain Sea clay when treated with five different cement-based binders. Champlain Sea clay, a marine clay, is commonly found in St. Lawrence Lowlands in eastern Canada. The unconfined compressive strength tests were conducted to measure the shear strength development of treated clay under different binder type, binder dosage, and curing time conditions. The scanning electronic microscopy (SEM) and X-ray diffraction (XRD) analyses were conducted to investigate the microstructural changes in the specimens. Based on the test results, it was found that cement is efficient to treat Champlain Sea clay with a significant strength improvement. For Champlain Sea clay used in this study, the optimum cement dosage was found to be around 100 kg/m3 per mixed volume in terms of strength improvement and cost-effectiveness. The clay samples treated with a mix of cement and cement kiln dust and a mix of cement with slag showed a substantial strength increase over time. These results proved the feasibility of using cement kiln dust mix or slag to replace a portion of cement in treating Champlain Sea clay. Based on SEM observations, a substantial transformation was observed in the microstructure of the clay due to cement mixing. A large amount of clay-binder aggregates were formed and the hydration products filled the porous network of the clay samples, which results in a strength improvement in the treated clay. Based on the XRD analysis, hydration products, such as calcium silicate hydrate and calcium tecto-dialumodisilicate tetrahydrate, were formed in the cement-treated clay specimens, which explains the strength improvement of Champlain Sea clay due to cement mixing.

Sources of atmospheric lead (Pb) after quarter century of phasing out of leaded gasoline in Bangkok, Thailand

After global phasing out of leaded gasoline, anthropogenic sources of atmospheric lead (Pb) are dominated by coal combustion emissions, high-temperature metallurgical processes, and vehicle exhausts. Thailand was one of the first countries in Southeast Asia to completely phase out leaded gasoline by the year 1994. This study investigates the sources of atmospheric Pb in Thai aerosols, a quarter-century after phasing out of leaded gasoline using a multiproxy approach, Pb isotopes in conjunction with trace metal composition of PM2.5. Aerosol samples were collected for 1 year from January 2018 to April 2019 from Bangkok and Chonburi to understand the influence of seasonal variation on aerosol chemistry. Bangkok is the only megacity in Thailand and notorious for traffic congestion and Chonburi is a coastal town, 80 km southeast of Bangkok where the inter monsoon winds make landfall. Aerosol Pb concentrations significantly decreased in 25 years from 74 ± 5 ng/m3 in 1994–1995 to 14 ± 13 ng/m3 measured in Bangkok during Northeast (NE) monsoon winds. Concentrations of all the metals are higher in Chonburi compared to Bangkok in the NE monsoon wind, owing to the addition of local emissions from the megacity over the long-range transported metals before the winds reach the coastal town. The Pb isotope ratios have a wide range (206Pb/207Pb range 1.1343–1.1685 and 208Pb/207Pb range 2.4138–2.4450) but the average ratios are not significantly different in Bangkok and Chonburi for all three seasons. However, present day 206Pb/207Pb ratios are more radiogenic than those measured 25 years ago in Bangkok. The Pb isotopes from both locations in all seasons have considerable overlap with unleaded gasoline and diesel used in Southeast Asia indicating automobile exhaust as an important source. Additionally, the NE monsoon winds are influenced by mixing of crustal dust (Al/Pb ratios correlates well with 206Pb/207Pb, r2 = 0.63) with coal combustion emission (strong inter-correlation of Pb, Zn, As and Cd, r2 from 0.72 to 0.94) from China and Vietnam. Pb isotopes of the Southwest (SW) monsoon winds are also influenced by crustal dust and falls on the mixing line between coal combustion and ore processing emission from India in a Pb triple isotope plot. Chemical composition of aerosols in the inter-monsoon winds are similar to SW monsoon winds. After a quarter-century of leaded gasoline banning in Thailand, the atmospheric Pb sources have changed from less radiogenic leaded gasoline exhaust and Chinese ore processing to more radiogenic unleaded gasoline and diesel exhaust and coal combustion.

Characterization of forest fire and Saharan desert dust aerosols over south-western Europe using a multi-wavelength Raman lidar and Sun-photometer

In the morning of 21 July 2019, a dense forest fire smoke plume was detected over Évora (Portugal) in the lower troposphere. Around 13:00 UTC, a Sahara dust layer was detected by lidar between 3000 and 4000 m height above sea level. In this work results of these events using an EARLINET Raman lidar and AERONET Sun-photometer measurements are reported and discussed: the dense smoke layer, the mixing of smoke with dust and the lofted dust layer that crossed Évora. During the morning, in-situ hourly mean black carbon concentration reached a maximum of 6.28 ± 0.73 μgm−3. The AERONET fine mode aerosol optical depth at 500 nm reached 0.77 and the Ångström exponent at 440–870 nm varied between 1.45 and 1.82, indicating the presence of fine smoke particles in the atmospheric column. In the beginning of the afternoon, the lidar profiles indicated the presence of a smoke layer followed by two thin layers of pollution mixed with dust and a lofted dust layer. The smoke particles caused low particle linear depolarization ratios at 532 nm with mean value of 0.059 ± 0.002 in the smoke layer. In contrast, the lofted dust layer caused mean particle linear depolarization ratio at 532 nm of 0.26 ± 0.01. Mass concentrations were in the order of 22–29 μg m−3 in the smoke layer and 60–178 μg m−3 in the lofted dust layer. During the afternoon and at night, mixing dust layers were identified by using lidar data. In the afternoon, two aerosol layers exhibited mean particle linear depolarization ratios at 532 nm of 0.23 ± 0.01 and 0.25 ± 0.01 with the dust dominating the extinction and mass concentration in both aerosol layers. Mass concentrations of dust were in the order of 101–266 μg m−3 and 159–195 μg m−3. At night, the particle linear depolarization ratio presented low variability across the identified layer with mean value of 0.20 ± 0.01. The Ångström exponents were low, the mean lidar ratios were 50 ± 6 sr (355 nm) and 42 ± 4 sr (532 nm) and the aerosol optical depth was 0.32 (355 nm) and 0.30 (532 nm). Mass concentrations ranged in 10–28 μg m−3 for non-dust and in 77–186 μg m−3 for dust.

Potential utilization of construction wastes in asphalt pavements as fillers using ranking framework

This study explored the potential of four construction wastes namely brick dust (BD), concrete dust (CD), glass powder (GP), and limestone dust (LD) as fillers in asphalt concrete mixes using a decision-based ranking framework. The asphalt concrete mixes containing aforesaid fillers were designed and their optimum asphalt content and effective filler-binder ratios were assessed. The mastics corresponding to the estimated filler-binder ratio were prepared and their viscoelastic properties, as well as resistance against fatigue and rutting resistance, were analyzed. Asphalt concrete mixes containing waste fillers were also assessed against cracking, moisture permeation, and rutting. Additionally, the economic benefits and environmental viability of various wasted were also compared. The aptness of fillers was evaluated using a ranking methodology; in which suitable weightage is given to different test results, based on possible conditions on the field by the decision-makers. Asphalt mix containing fine fillers (LD, CD, and GP) exhibited superior resistance against rutting as well as cracking resistance. Asphalt mixes containing CD and LD displayed better moisture resistance due to the calcium-based minerals in them. Mixes containing LD and BD fillers were found to be more economical and environmentally friendly than conventional stone dust mixes. Based on the suggested ranking methodology, LD and GP emerged as the best and poor performing fillers respectively.

Physico-mechanical properties of cement bonded ceiling board developed from teak and African locust bean tree wood residue

Abstract Over the years, the pursuit for locally sourced economical and environmentally safe materials has been on the increase in the development of composite boards. These locally sourced materials are organic materials from plants and livestock such as wood residue, feathers, rice husk, maize husk and bamboo fiber. Therefore, this study utilizes species of wood residue in the development composite ceiling boards. Ceiling boards were developed from teak and African locust bean tree wood residue using cement as a binder. The ceiling boards were made by varying the composite mass of the mix and mixing ratio of wood dust to cement. A constant load of 5 kN was used for the compaction process using a hydraulic pressing machine. Physico-mechanical properties of the ceiling boards such as moisture content, density, water absorption, drying shrinkage, tensile strength, and compressive strength were evaluated. The percentage of moisture content were 9.50 and 14.50% for teak and African locust bean tree wood dust, respectively. The values of density varied from 0.56 − 0.68 g/cm3. The water absorption ranged from 9.0 to 39.8% after 24 h immersion and drying shrinkage ranged from 8.60 to 35%. The maximum impact energy obtained is 98 J. The highest tensile, compressive and flexural strengths for the ceiling boards were 1.09, 0.82, and 0.56 MPa, respectively. The composite samples showed that ceiling boards made from teak wood dust is most suitable for interior use. Cement was found to be suitable as a binder for the development of ceiling boards.

Aerosol‐Radiation Interactions of Dust Storm Deteriorate Particle and Ozone Pollution in East China

AbstractEast Asia features frequent dust storms and intensive anthropogenic emissions. The mixing of natural dust and anthropogenic pollutants exerts complicated impacts on air pollution and regional climate. Studies have focused on chemical interactions of the mixed pollution, while the meteorological feedback and influences on atmospheric chemistry have not been fully investigated. Here, a comprehensive study on a widespread dust storm and its influence on the air quality downwind was conducted by combining multiple observations and modeling. We found that dust originated from Gobi Desert was mixed with anthropogenic pollutants after transported to the Yangtze River Delta (YRD). Through scattering and absorbing radiation, dust aerosol perturbed solar energy budget and led to a more stabilized planetary boundary layer (PBL). A reduction of 15% in PBL height (184 m) weakened the dispersion of locally emitted pollutants and increased primary pollution by 10% in YRD city clusters. Besides, the mixed plume over offshore areas warmed the entire lower atmosphere and increased surface evaporation. Accordingly, ozone formation was accelerated by ∼1 ppbv/h within PBL under higher temperature, and secondary aerosol was increased due to faster photochemical and heterogeneous oxidation. Such enhancements substantially contributed to air quality deterioration in YRD region. This work reveals the complexity of interactions between natural dust and anthropogenic pollutants through both atmospheric chemistry and meteorological feedbacks, which is of great importance in both regional air pollution and climate.

Tracking the changes of iron solubility and air pollutants traces as African dust transits the Atlantic in the Saharan dust outbreaks

We studied the solubility, in real sea water, of iron present in the African dust outbreaks that traverse the Atlantic. Based on measurements of soluble iron (sFe) and aerosol chemistry, we found iron solubilities within the range of 0.4–1.8% in Tenerife, 0.4–3.1% in Barbados and 1.6–12% in Miami. We apportioned the concentrations of sFe between the three sources and processes that we identified: (1) dust, (2) heavy fuel oil combustion emissions, associated with an excess of vanadium and nickel, and (3) atmospheric processing, which is influenced by acidic pollutants. We tracked the propagation of the dust-front of the African dust outbreaks across the Atlantic, which are associated with dust peak events at the impacting sites. During the westward transport across the Atlantic, the contribution to sFe from dust decreased (63%, 43% and 9% in Tenerife, Barbados and Miami, respectively), whereas the contribution due to atmospheric processing increased (26%, 45% and 74% in Tenerife, Barbados and Miami, respectively). In these Saharan-dust outbreaks, the concentrations of sFe due to heavy fuel oil combustion were significantly lower (mostly < 5 ng/m3) than those in the polluted marine atmosphere (10–200 ng/m3). The overall results are consistent with the idea that the mixing of dust with acid pollutants increases the solubility of iron during the African-dust outbreaks that traverse the Atlantic.

Unveiling the stellar origin of the Wolf–Rayet nebula NGC 6888 through infrared observations

ABSTRACT We present a comprehensive infrared (IR) study of the iconic Wolf–Rayet (WR) wind-blown bubble NGC 6888 around WR 136. We use Wide-field Infrared Survey Explorer, Spitzer IRAC, and MIPS and Herschel PACS IR images to produce a sharp view of the distribution of dust around WR 136. We complement these IR photometric observations with Spitzer IRS spectra in the 5–38-μm wavelength range. The unprecedented high-resolution IR images allowed us to produce a clean spectral energy distribution, free of contamination from material along the line of sight, to model the properties of the dust in NGC 6888. We use the spectral synthesis code cloudy to produce a model for NGC 6888 that consistently reproduces its optical and IR properties. Our best model requires a double distribution with the inner shell composed only of gas, whilst the outer shell requires a mix of gas and dust. The dust consists of two populations of grain sizes, one with small-sized grains asmall = [0.002–0.008] $\mu$m and another one with large-sized grains abig = [0.05–0.5] $\mu$m. The population of big grains is similar to that reported for other red supergiants stars and dominates the total dust mass, which leads us to suggest that the current mass of NGC 6888 is purely due to material ejected from WR 136, with a negligible contribution of the swept up interstellar medium. The total mass of this model is 25.5$^{+4.7}_{-2.8}$ M⊙, a dust mass of $M_\mathrm{dust} = 0.14^{+0.03}_{-0.01}$ M⊙, for a dust-to-gas ratio of 5.6 × 10−3. Accordingly, we suggest that the initial stellar mass of WR 136 was ≲50 M⊙, consistent with current single stellar evolution models.