Average Dust Research Articles

Spatial Variations of Dust Opacity and Grain Growth in Dark Clouds: L1689, L1709, and L1712

The far-infrared (FIR) opacity of dust in dark clouds within the Ophiuchus molecular cloud is investigated through multiwavelength infrared observations from UKIDSS, Spitzer, and Herschel. Employing the infrared color excess technique with both near-infrared and mid-infrared photometric data, a high-resolution extinction map in the K band (A K ) is constructed for three dark clouds: L1689, L1709, and L1712. The derived extinction map has a resolution of 1′ and reaches a depth of A K ∼ 3 mag. The FIR optical depths τ 250 at a reference wavelength of 250 μm are obtained by fitting the Herschel PACS and SPIRE continuum data at 100, 160, 250, 350, and 500 μm using a modified blackbody model. The average dust opacity per unit gas mass at 250 μm, r κ 250, is determined through a pixel-by-pixel correlation of τ 250 with A K , yielding a value of approximately 0.09 cm2 g−1, which is about 2–3 times higher than the typical value in the diffuse interstellar medium. Additionally, an independent analysis across 16 subregions within the Ophiuchus cloud indicates spatial variations in dust opacity, with values ranging from 0.07 to 0.12 cm2 g−1. Although the observed trend of increasing dust opacity with higher extinction implies grain growth, our findings indicate that rapid grain growth has clearly not yet occurred in the dark clouds studied in this work.

Study on the characteristics of compound dust source pollution and foam dust suppression technology in coal mine anchor excavation production

To guard against the damage caused by the dust pollution of the shuttle driver in the anchor excavation production, the Discrete Phase Model(DPM)-Discrete Element Model(DEM) was constructed based on the gas-solid two-phase flow theory, the dust pollution characteristics of the shuttle transfer stage were numerically simulated, and a dual carborne combined foam dust suppression system was developed. The results showed that at the rear of the transfer machine, due to the reduction of the roadway section space during transferring made the wind velocity relatively maximum, and the space after transferring dispersed many cutting dust and transferring dust, resulting in the wind velocity after transferring was slightly smaller than before transferring, and the wind velocity difference was 0.18 m/s on average. The dust pollution in the operating environment of the shuttle driver before, during and after transferring was more serious, with 162.1 mg/m³, 340.7 mg/m³ and 540.8 mg/m³. There was variability in the particle diameter of dust generated by different processes, and smaller micron-sized dust particles were generated during transferring, of which respiratory dust below 7.07 μm accounted for up to 21% of the total. To reduce the high concentration of respiratory dust clusters, a strong wettability high-fold foam dust suppressant was prepared and applied to a dual carborne combined foam dust suppression system, and the average dust reduction rates of total dust and respiratory dust reached 91.9% and 93.6%, respectively.

Numerical simulation of the dust pollution characteristics and the optimal dustproof air volume in coal washing plant screening workshop

Dust pollution generated during the working process of a screening workshop in a coal washing plant seriously threatens the occupational health of workers. To improve the working environment for workers, we investigated the effects of various airflow parameters on the diffusion of dust particles and pollutants. We established a proportional model of the screening workshop and conducted spatiotemporal analysis of the evolution laws of airflow and particulate matter. We used numerical simulation and on-site measurements to obtain the optimal dust removal air flow rate in a coal washing plant workshop. When the air flow rate is between 360 and 1260 m³/min, the overall dust concentration in the workshop and the average dust mass concentration in the breathing zone decrease significantly as the air flow rate increases. However, if the air flow rate is too high, this can cause re-entrainment of dust, which will pollute the operation area again. The optimum dust removal airflow for the inlet air was 1260 m³/min. This air flow rate decreases the dust at the height of the breathing zone in the working area, and the dust concentration at the sidewalk in the working area decreases by 58.82%. This air flow rate can act as a reference value for workshop ventilation design to provide a clean and safe production environment for coal miners. Our methodology and results are of value the formulation and development of effective dust control and clean production technologies.

Assessment of the Spraying System Impact at the Preparation Stage of Iron Ore Concentrate Products

Introduction. Harmful components of ore dust, formed during the unloading of products in the preparation of iron ore concentrate (PPIOC) at the mixing stage, cause damage to both workers and equipment. To address this issue, liquid aerosol spraying using nozzles with large diameters (>20 μm) is used. However, this method proves ineffective in capturing fine-dust particles. Therefore, enhancing the efficiency of the dust deposition method through PPIOC dust spraying becomes a pressing challenge. The aim of this study is to investigate the impact of the Dry Fog technology, generating liquid droplets up to 20 μm in size, during the unloading stage of PPIOC at a mining and metallurgical enterprise in the precipitation of suspended fine-dust particles. The primary goal of this research was to assess the effectiveness and potential advantages of applying the Dry Fog technology for dust spraying with subsequent precipitation, as this technology has not been previously applied to PPIOC dust.Materials and Methods. The experiment on the PPIOC dust deposition was conducted in a specially designed laboratory setup. Through physical modeling in the laboratory setup, parameters of the precipitation process were obtained. Subsequently, the results were analyzed to understand the dependence of dust precipitation over time, taking into account the influence of the Dry Fog technology. An experiment program was developed for physical modeling. According to the devised program, dust was uniformly loaded into the interior of the laboratory setup (from the top), distributed in the air stream throughout the volume of the setup by a fan, and an instrument located at the bottom recorded changes in concentration over time. Experiments on dust precipitation were then conducted using liquid spraying (filtered water as the liquid) introduced into the setup through nozzles generating droplets with sizes of 10 and 15 μm, concurrently with the loading of dust into the laboratory setup. The effectiveness of the Dry Fog technology in the deposition of PPIOC dust was determined visually and further analyzed based on a comparison of graphs. The dynamics of changes in the average dust concentrations depending on time was studied both during precipitation without spraying and using the Dry Fog technology. During the experiment, the characteristics of the microclimate inside the laboratory setup (humidity, temperature and air velocity) and the parameters of two nozzles — their operating pressure and the supplied liquid spraying time — were recorded.Results. The comparison of the results showed a reduction in the dust precipitation time by 40 % and 75 % when using nozzles with sizes of 10 μm and 15 μm, respectively.Discussion and Conclusion. The experiment results confirm the effectiveness of the Dry Fog technology for PPIOC dust precipitation during unloading at the mixing stage. Fundamental findings have been obtained, providing a basis for further assessment of the efficiency of dust precipitation with the additional application of pulsating ventilation. In such a combination, an additional 20–25 % increase in precipitation efficiency is anticipated compared to the results presented in this article. The obtained results will support the justification of rational parameters and the implementation of the described method in production to enhance dust precipitation efficiency. Additionally, they will aid in developing a methodology to accelerate the PPIOC dust precipitation using the pulsating ventilation method.

Determination of the Convergence of Intra-Laboratory Measurements of Dust Content on a Construction Site

Introduction. Intra-laboratory comparison tests play an important role in ensuring the quality and reliability of research outcomes in laboratories. These tests allow researchers to evaluate the accuracy and reproducibility of the methods they use in their work, as well as to identify potential sources of error and inconsistency. The results of these tests are shared with experts to confirm competence within the accreditation. Typically, comparison tests are carried out in laboratory conditions in a familiar and calm environment for the testers. However, when laboratories conduct research as part of a special assessment of working conditions (SAWC) they are required to conduct on-site comparisons at real-world facilities, where customers may unwittingly disrupt the process and directly affecting the quality of the measurements. The aim of this study is to evaluate the quality of on-site intra-laboratory comparison tests using the example of determining the dust content in a bricklayer's work environment on a construction site, and to determine the minimum number of measurements necessary and sufficient for this purpose.Materials and Methods. To determine the dustiness of the bricklayer's workplace, a weighing method was used. This involved collecting dust on filters and then weighing them to determine the concentration. The quality assessment of intra-laboratory tests was conducted in accordance with GOST R ISO 5725-1-2002 "Accuracy (trueness and precision) of measurement methods and results. Part 1. General principles and definitions".Results. At the bricklayer's workplace, a 1.6-fold excess of the one-time maximum permissible dust concentration was detected. The average dust concentration at the workplace under study was: Kp2 = 9.57 ± 0.81 mg/m3, the convergence of the results obtained was r = 8.68 %, the relative error δ = 8.50 %. It was revealed that the maximum allowable difference between the results of the two tests was 0.84 mg/m3. The difference in direct measurements of the mass of the two samples should be no more than 0.1 mg.Discussion and Conclusion. The results obtained demonstrated the possibility of conducting a minimum number of measurements that, under reproducible conditions, are considered satisfactory and could be provided to experts for confirming the competence of the laboratory. As part of a special assessment of working conditions, employees of the object under study are recommended to use personal respiratory protection equipment that offers protection against highly dispersed dust particles.

Real-time in situ monitoring of dust particle growth in a low-pressure nanodusty plasma based on laser-induced photodetachment

Particulate matter air pollution in the form of ultrafine dust is a growing global concern. In this Letter, we will use a nanodusty Ar/HMDSO plasma as a model system for a heavily contaminated gas and we present the development of a technique for real-time in situ measurements of the dust particle size. The method is based on laser-induced photodetachment of bound electrons from the surface of dust particles. These photo-released electrons are measured as an increase in the free electron density of the plasma using microwave cavity resonance spectroscopy. We show that instead of reconstructing the entire resonance profile, the temporal response of a single microwave frequency was enough to perform the measurements. More specifically, the decay timescale of the cavity response can be interpreted as the re-charging timescale of the dust particles. Then, using a stochastic model, this timescale can be modeled, which eventually retrieves the dust particle size. We found good agreement between the predicted dust particle size and the average dust particle size obtained from ex situ scanning electron microscopy measurements. This method allows for the real-time monitoring of the dust particle size and a controlled production of nanometer-scale dust particles, which gives opportunities both for fundamental dusty plasma physics and models, as well as for applications in monitoring ultrafine dust air pollution.

A Galactic Eclipse: The Small Magellanic Cloud Is Forming Stars in Two Superimposed Systems

The structure and dynamics of the star-forming disk of the Small Magellanic Cloud (SMC) have long confounded us. The SMC is widely used as a prototype for galactic physics at low metallicity, and yet we fundamentally lack an understanding of the structure of its interstellar medium (ISM). In this work, we present a new model for the SMC by comparing the kinematics of young, massive stars with the structure of the ISM traced by high-resolution observations of neutral atomic hydrogen (H i) from the Galactic Australian Square Kilometre Array Pathfinder survey. Specifically, we identify thousands of young, massive stars with precise radial velocity constraints from the Gaia and APOGEE surveys and match these stars to the ISM structures in which they likely formed. By comparing the average dust extinction toward these stars, we find evidence that the SMC is composed of two structures with distinct stellar and gaseous chemical compositions. We construct a simple model that successfully reproduces the observations and shows that the ISM of the SMC is arranged into two superimposed, star-forming systems with similar gas mass separated by ∼5 kpc along the line of sight.

Distribution of Motor Vehicle Volumes and Ambient Air Dust Levels in Hot Points of Yogyakarta City, Indonesia

Introduction: Yogyakarta City, Indonesia is a center for tourism, government, education, and the economy. In line with increasing mobility and transportation, this situation has a positive impact economically, but a negative impact in terms of air pollution due to vehicle emissions. Motorized vehicles contribute to air pollution reaching 66.34% of total pollution. PM2.5 is a critical parameter in the city of Yogyakarta. Methods: This research aims to determine the volume of motorized vehicle traffic and the distribution of dust levels in the ambient air of Yogyakarta City. Data collection used non-probability purposive sampling with the roadside method. Vehicle volume is mapped using hotspots and dust levels using interpolation. Results and Discussion: The average vehicle volume in the morning was 2,293.147 pcu/hour and in the afternoon it was 2,301.173 pcu/hour. The hotspot results showed that the volume of motorized vehicles in the morning category was very high at 2,921.600-5,655 pcu/hour and in the afternoon it was 3,678.800-4,558 pcu/hour. The average dust content in the morning is 0.10667 grams/m3 and in the afternoon it is 0.10240 grams/m3. The interpolation results showed that the distribution of dust levels in the very high category in the morning was 0.17000-0.20000 grams/m3 and in the afternoon it was 0.21000-0.26000 grams/m3. Conclusion: The highest average volume of vehicles occurs in the afternoon while the highest total dust content occurs in the morning.

On the dust properties of the UV galaxies in the redshift range z ∼ 0.6–1.2

ABSTRACT Far-infrared observations from the Herschel Space Observatory are used to estimate the infrared (IR) properties of ultraviolet-selected galaxies. We stack the PACS (100, 160 $\mu$m) and SPIRE (250, 350, and 500 $\mu$m) maps of the Chandra deep field south (CDFS) on a source list of galaxies selected in the rest-frame ultraviolet (UV) in a redshift range of 0.6–1.2. This source list is created using observations from the XMM–OM telescope survey in the CDFS using the UVW1 (2910 Å) filter. The stacked data are binned according to the UV luminosity function of these sources, and the average photometry of the UV-selected galaxies is estimated. By fitting modified black bodies and IR model templates to the stacked photometry, average dust temperatures and total IR luminosity are determined. The luminosity-weighted average temperatures are consistent with a weak trend of increasing temperature with redshift found by previous studies. Infrared excess, unobscured, and obscured star formation rate (SFR) values are obtained from the UV and IR luminosities. We see a trend in which dust attenuation increases as UV luminosity decreases. It remains constant as a function of IR luminosities at fixed redshift across the luminosity range of our sources. In comparison to local luminous infrared galaxies with similar SFRs, the higher redshift star-forming galaxies in the sample show a lesser degree of dust attenuation. Finally, the inferred dust attenuation is used to correct the unobscured SFR density in the redshift range 0.6–1.2. The dust-corrected SFR density is consistent with measurements from IR-selected samples at similar redshifts.

Comparative Study of Exposure Assessment of Dust in Building Materials Enterprises Using ART and Monte Carlo

BackgroundDust generated during the processing of building materials enterprises can pose a serious health risk. The study aimed to compare and analyze the results of ART and the Monte Carlo model for the dust exposure assessment in building materials enterprises, to derive the application scope of the two models. MethodsFirst, ART and the Monte Carlo model were used to assess the exposure to dust in each of the 15 building materials enterprises. Then, a comparative analysis of the exposure assessment results was conducted. Finally, the model factors were analyzed using correlation analysis and the scope of application of the models was determined. ResultsThe results show that ART is mainly influenced by four factors, namely, localized controls, segregation, dispersion, surface contamination, and fugitive emissions, and applies to scenarios where the workplace information of the building materials enterprises is specific and the average dust concentration is greater than or equal to 1.5 mg/m3. The Monte Carlo model is mainly influenced by the dust concentration in the workplace of building materials enterprises and is suitable for scenarios where the dust concentration in the workplace of the building materials enterprises is relatively uniform and the average dust concentration is less than or equal to 6mg/m3. ConclusionART is most accurate when workplace information is specific and average dust concentration is > 1.5 mg/m3; whereas, The Monte Carlo model is the best when dust concentration is homogeneous and average dust concentration is < 6 mg/m3.

Study on the fine particles deposition law in the bronchus of miners affected by dust pollution in the anchor excavation working environment

To study the dust exposure law of the operator in the anchor digging working face, the CFD-DEM method was used to numerically simulate the dust deposition pattern in the bronchus of the anchor digging driver. The results show that the highest dust concentration in the vortex region of the anchor digging working face can reach 2364.76 mg/m3, seriously endangering the health of anchor digging driver. The average dust concentration in the respiratory hemisphere of the driver is 510.57 mg/m3, and the range of inhaled dust diameter is 0–60 μm in the breathing state of moderate labour. Over time, the deposition mass in the bronchial showed a pattern of rapid and then slow increase, which was consistent with the trend of the Boltzmann model. Increasing dust particle diameter was positively correlated with bronchial deposition rate and negatively correlated with alveolar deposition rate. Among them, 0–10 μm particles were deposited throughout the bronchus and a large number of particles were deep into the alveoli, with the alveolar deposition rate as high as 56.3 %, while the alveolar deposition rate for particles of 10–20 μm decreased to 20.4 %, and for particles larger than 30 μm, the effect on the alveoli was smaller.

Experimental study on the influence of longitudinal slope on airflow-dust migration behavior after tunnel blasting.

In this paper, a 1:21 model experiment was conducted to discuss the dust diffusion efficiency and liner trolley obstruction effect inside the tunnel at - 9% to 9%, the effect of different initial dust concentrations on dust diffusion and liner trolley obstruction effect at 6% slope, and the effect of different return air velocity on dust diffusion at 6% slope, the reliability of the results is verified by computational fluid dynamics simulations. The results show that as the slope of the tunnel changes from 0 to - 9%, the average dust diffusion time decreases by 3.7% at the working face and the dust concentration difference between the front and rear of the trolley is improved by 2.7%. When the slope of the tunnel changes from 0 to - 9%, the average dust diffusion time increases by 7.2% at the working face and the dust concentration difference between the front and rear of the trolley is improved by 17.9%. With each 100mg/m3 increase in the initial dust concentration, the dust diffusion time at the working face and the tunnel exit increases by 9.15% and 8.17% on average, and the lining trolley obstruction time increases by 23.33s on average. The dust diffusion times take an average reduction rate of 15.7%, with the increase of return air velocity. The recommended return air velocity is greater than 1m/s for large slope tunnels. When the slope changes from 0° to 9°, the hindrance rate of slope on dust diffusion is 2.88462%, 8.65385%, and 16.34615% respectively. Dust diffusion efficiency will be reduced as the tunnel slope changes from 0° to 9°, The growth rate of slope on dust diffusion is - 0.96154%, - 2.88462%, and - 6.73077% respectively.

Characteristics of Atmospheric Dust Fall Pollution and Its Chemical Composition and Mass Reconstruction in Mentougou District of Beijing

To study the characteristics of atmospheric dust fall pollution in Mentougou District of Beijing, the monthly average monitoring results of 57 atmospheric dust fall samples from two state-controlled ambient air stations in Mentougou District from 2018 to 2022 were collected, and the atmospheric dust fall pollution status and its time variation characteristics in Mentougou District were analyzed. In order to explore the characteristics of chemical components of atmospheric dust fall and the results of quality mass reconstruction and their sources, 57 dust fall samples were collected using the active suction method at the Sanjiadian State-controlled Ambient Air Station. The mass concentration of dust fall and its chemical components were measured, the characteristics of chemical components in atmospheric dust fall were studied, and the mass reconstruction of the main components of atmospheric dust fall was performed using particle mass reconstruction technology. The reliability of the mass reconstruction results and the reasons for its undetermined components were also discussed. The results showed that from 2018 to 2022, the monthly dust fall in Mentougou District of Beijing changed periodically, being the maximum in April or May in spring and the minimum in October or November in autumn, and the maximum monthly dust fall was 3.2 to 8.4 times the minimum monthly dust fall. The order of the quarterly average monthly dust fall was as follows:spring>summer>autumn>winter, and the dust fall mainly came from spring and summer, accounting for 40.1%-43.0% and 23.8%-37.5% of the total annual dust fall, respectively. The annual average monthly dust fall in Mentougou District of Beijing showed a significant downward trend. The dust fall in 2022 had decreased by 52.8% compared with that in 2018, with an average annual decline of 13.2%, which was related to the improvement in the fine management level of urban environmental protection in Beijing in recent years. In 2021, soil dust had a significant impact on dust fall in Mentougou District, with an actual contribution of 44.2%. The chemical components in the atmospheric dust fall in Mentougou District were mainly water-soluble ions, crustal elements, organic carbon(OC), and elemental carbon(EC). The total mass of the measured chemical components accounted for 65.0% of the mass fraction of the dust fall. The secondary organic carbon(SOC) was also an important component of the atmospheric dust fall, and its mass concentration was 13.5 μg·m-3, accounting for 96.4% of the mass fraction of OC. The main components of atmospheric dust fall mass reconstruction were crust element fugitive dust, organic matter(OM), SO42-, NO3-, NH4+, trace elements, EC, and Cl-, with mass concentrations of 34.8, 28.0, 20.6, 15.0, 5.6, 4.3, 3.2, and 2.2 μg·m-3, accounting for 25.5%, 20.6%, 15.1%, 11.1%, 4.1%, 3.2%, 2.3%, and 1.6% of the dust fall quality, respectively. The atmospheric dust fall mainly came from the soil dust, construction cement dust, biomass combustion, waste incineration, and secondary transformation process. The measured mass concentration of atmospheric dust fall had a good correlation with the reconstructed mass concentration of chemical components, and the determination coefficient R2 was 0.8173. The undetermined components in the mass reconstruction results accounted for 16.5% of the dust fall mass, of which the particle bound water(PBW) in the dust fall accounted for 6.2% of the dust fall mass, and the remaining undetermined components might have been related to the unmeasured components, the selected estimation coefficient of OM and crustal elemental dust, the particle size composition, the selected chemical component analysis method, and its measurement error.

Justification of an Energy-Efficient Air Purification System in Subways Based on Air Dust Content Studies

It is not uncommon that subways count as densely populated areas, so air quality standards, including fine dust concentration, have been established for them. As passengers and subway staff are exposed to potentially harmful airborne particles, addressing this issue is vital to ensuring a safe and healthy environment on the subway. To reduce the dust concentration in subway systems, the authors propose installing filters to capture dust in ventilation failures between subway tunnels near metro stations. A novel aspect of the proposed method is the fact that airflow will be moved through filters by using the piston action of trains passing through the tunnels. The result of this research provides empirical evidence regarding dust content and mass concentrations of PM2.5 and PM10 in subway environments. While some existing literature discusses air quality in subways, the inclusion of specific measurements and data from the experiment strengthens the understanding of the severity of dust-related air quality issues in such environments. The data for this study were collected in the Almaty subway (Republic of Kazakhstan) at four stations: Raiymbek Batyr, Almaty, Baikonur and Alatau. Measuring points were located on passenger platforms, in the halls and at the entrances to the station. The lab scale tests determined the percentage of particles by their diameters relative to the total volume of dust, the percentage of dust particles smaller than a certain diameter, the percentage of various metal oxides and the average dust density. A preliminary energy assessment has been done on the proposed method of air purification from dust. With a frequency of 24 pairs of trains per hour, the energy savings per ventilation failure will be 240.170 kWh.

ALMA Lensing Cluster Survey: average dust, gas, and star-formation properties of cluster and field galaxies from stacking analysis

ABSTRACT We develop new tools for continuum and spectral stacking of Atacama Large Millimeter/submillimeter Array (ALMA) data, and apply these to the ALMA Lensing Cluster Survey. We derive average dust masses, gas masses, and star-formation rates (SFRs) from the stacked observed 260-GHz continuum of 3402 individually undetected star-forming galaxies, of which 1450 are cluster galaxies and 1952 field galaxies, over three redshift and stellar mass bins (over z = 0–1.6 and log$M_{*} \, [{\rm M}_{\odot }] = 8$–11.7), and derive the average molecular gas content by stacking the emission line spectra in a SFR-selected subsample. The average SFRs and specific SFRs of both cluster and field galaxies are lower than those expected for main-sequence (MS) star-forming galaxies, and only galaxies with stellar mass of log$M_{*} \, [{\rm M}_{\odot }] = 9.35$–10.6 show dust and gas fractions comparable with those in the MS. The ALMA-traced average ‘highly obscured’ SFRs are typically lower than the SFRs observed from optical to near-infrared spectral analysis. Cluster and field galaxies show similar trends in their contents of dust and gas, even when field galaxies were brighter in the stacked maps. From spectral stacking we find a potential CO (J = 4 → 3) line emission (signal-to-noise ratio being ∼4) when stacking cluster and field galaxies with the highest SFRs.

Numerical simulation of dust control technology for longwall working face with convective air curtain.

A convection-type air curtain dust control system and method were proposed to effectively control the high dust concentrations generated during the operation of coal miners and hydraulic supports and to reduce the dust concentration in the entire working space of longwall work surfaces, and the effectiveness of air curtain dust control during single process operation was investigated through numerical simulation. The results showed that when the miner was working alone, there was a significant difference in the concentration distribution inside and outside the dust-proof air curtain, with significantly lower dust concentrations in the area where the miner drivers were operating compared to both sides, with an average dust mass concentration of around 420 mg/m3. Dust concentrations increased to about 700 mg/m3, but large amounts of dust were prevented from diffusing downwind. This indicates that the dust reduction effect is more pronounced after the equipment is opened, which can improve the working environment and reduce the probability of dust combustion and explosion accidents.

The physical and chemical structure of Sagittarius B2

Context. Sagittarius B2 (Sgr B2) is a giant molecular cloud complex in the central molecular zone of our Galaxy hosting several sites of high-mass star formation. The two main centers of activity are Sgr B2(M) and Sgr B2(N), which contain 27 and 20 continuum sources, respectively. Our analysis aims to be a comprehensive modeling of each core spectrum, where we take the complex interaction between molecular lines, dust attenuation, and free-free emission arising from H II regions into account. In this work, which is the first of two papers on the complete analysis, we determine the dust and, if H II regions are contained, the parameters of the free-free thermal emission of the ionized gas for each core, and derive a self-consistent description of the continuum levels of each core. Aims. Using the high sensitivity of ALMA, we characterize the physical and chemical structure of these continuum sources and gain better insight into the star formation process within the cores. Methods. We used ALMA to perform an unbiased spectral line survey of all 47 sources in ALMA band 6 with a frequency coverage from 211 to 275 GHz. In order to model the free-free continuum contribution of a specific core, we fit the contained recombination lines to obtain the electron temperatures and the emission measures, where we use an extended XCLASS program to describe recombination lines and free-free continuum simultaneously. In contrast to previous analyses, we derived the corresponding parameters here not only for each core, but also for their local surrounding envelope, and determined their physical properties. Results. The distribution of recombination lines we found in the core spectra closely fits the distribution of H II regions described in previous analyses. In Sgr B2(M), the three inner sources are the most massive, whereas in Sgr B2(N) the innermost core A01 dominates all other sources in mass and size. For the cores we determine average dust temperatures of around 236 K (Sgr B2(M)) and 225 K (Sgr B2(N)), while the electronic temperatures are located in a range between 3800 and 23 800 K. Conclusions. The self-consistent description of the continuum levels and the quantitative description of the dust and free-free contributions form the basis for the further analysis of the chemical composition of the individual sources, which is continued in the next paper. This detailed modeling will give us a more complete picture of the star formation process in this exciting environment.

CFD Simulation Based Ventilation and Dust Reduction Strategy for Large Scale Enclosed Spaces in Open Pit Coal Mines—A Case of Coal Shed

The coal shed is an enclosed space where raw coal is stored and handled. The intensive operation of the machinery inside the coal shed generates a large amount of dust, and the wind speed inside the enclosed space easily leads to a high concentration of dust, which endangers the physical and mental health of the workers. In this paper, we first studied the particle size distribution of dust samples in the coal shed and found that 12.2% of the dust in the air of the coal shed was 10–100 μm, 87.8% was less than 10 μm, and 72.9% was less than 2.5 μm. Fluent was used to simulate the law of dust dispersion in the coal shed under different working conditions, and finally, the simulation results were used to guide the design of the ventilation site and dust-reduction scenario. The experimental and simulation results show that under the same working conditions, the average dust reduction efficiency of the ventilation method in which the north side and south side pump air outside was 9.9%. The ventilation method in which the north side blows inside and the south side pumps outside was 23.7%. The average dust reduction efficiency of the ventilation method in which the north side blows inside and the south side pumps outside + placing the fan in the middle was 59.9%. The research results can provide some reference value for indoor air quality improvement.

Influence of Technological Housing Conditions on the Concentration of Airborne Dust in Dairy Farms in the Summer: A Case Study.

This research shows the size composition of airborne dust fractions in selected dairy barns down to the smallest particles, including factors that influence this composition. Measurements with a Dust-Track 8530 laser photometer took place in the summer at external temperatures of 29.5 to 36 °C. In barns with straw bedding, the average total dust concentration TDC was 66.98 ± 28.38 μg·m-3 (PM10 60.11 ± 19.93 μg·m-3, PM4 49.48 ± 13.76 μg·m-3, PM2.5 44.78 ± 10.18 μg·m-3, and PM1 38.43 ± 9.29 μg·m-3). In barns without straw bedding, the average TDC was 55.91 ± 36.6 μg·m-3, PM10 33.71 ± 13.86 μg·m-3, PM4 30.69 ± 15.29 μg·m-3, PM2.5 27.02 ± 13.38 μg·m-3, and PM1 22.93 ± 10.48 μg·m-3. The largest TDC of 108.09 ± 32.93 μg·m-3 (PM10 69.80 ± 18.70 μg·m-3, PM4 68.20 ± 18.41 μg·m-3, PM2.5 53.27 ± 14.73 μg·m-3, and PM1 38.46 ± 5.55 μg·m-3) was measured in an old cowshed with stanchion housing for 113 cows, straw bedding, and ventilation through windows. In a modern cowshed for loose housing of 440 lactating cows without straw bedding, with natural ventilation and 24 axial fans, TDC was 53.62 ± 49.52 μg·m-3, PM10 20.91 ± 5.24 μg·m-3, PM4 17.11 ± 3.23 μg·m-3, PM2.5 13.71 ± 0.92 μg·m-3, and PM1 12.69 ± 2.82 μg·m-3. In all investigated barns, a large proportion of airborne dust particles (54.38 ± 20.82% of TDC) consists of the smallest PM1 dust particles (from 12.69 ± 2.82 μg·m-3 to 48.48 ± 1.18 μg·m-3).

The evaluation analysis on the airborne dust regional pollution of the anchor drilling operation in the tunnel.

The anchor drilling operations generate massive airborne dust particles in the tunnel heading face that raises the pneumoconiosis morbidity and explosion risk. In this paper, a full-scale tunnel physical model is constructed to study the effect of the wind velocity and drilling site position on the airborne dust regional pollution scope based on the actual anchor drilling craft. The research indicates that the four extensive vortex areas keep the dust suspension at 14m from the heading face and make the deposition dust particle refloat. The average respirable dust rate reaches the maximum value at section 5m and presents a gradual decline as the dust particle migrates along the outlet direction. Raising the wind velocity contributes to alleviating the airborne dust pollution in the anchor drilling operation. As the wind velocity increases from 3 to 24m/s, the high dust concentration area and number higher than 200mg/m3 pose overall decrease trends, and the average dust concentration displays a linear decrease until 26.14-58.65mg/m3 around the anchor worker head. Moving the drilling site positions closer to the exhaust air duct aggravates the airborne dust pollution in the front breathing zone. As the anchor drilling operation switches from the return air side to the supply air side, the dust concentration area ascends by 59.4-84.4% in the personnel respiratory space.