Concentration Of Suspended Particles Research Articles

A review on rheological models and mathematical problem formulations for blood flows

A review on constitutive equations proposed for mathematical modeling of laminar and turbulent flows of blood as a concentrated suspension of soft particles is given. The rheological models of blood as a uniform Newtonian fluid, non-Newtonian shear-thinning, viscoplastic, viscoelastic, tixotropic and micromorphic fluids are discussed. According to the experimental data presented, the adequate rheological model must describe shear-thinning tixotropic behavior with concentration-dependent viscoelastic properties which are proper to healthy human blood. Those properties can be studied on the corresponding mathematical problem formulations for the blood flows through the tudes or ducts. The corresponding systems of equations and boundary conditions for each of the proposed rheological models are discussed. Exact solutions for steady laminar flows between the parallel plates and through the circular tubes have been obtained and analyzed for the Ostwald, Hershel-Bulkley, and Bingham shear-thinning fluids. The influence of the model parameters on the velocity profiles has been studied for each model. It is shown, certain sets of fluid parameters lead to flattening of the velocity profile while others produce its sharpening around the axis of the channel. It is shown, the second-order terms in the viscoelastic models give the partial derivative differential equations with high orders in time and mixed space-time derivatives. The corresponding problem formulations for the generalized rhelogical laws are derived. Their analytical solutions in the form of a normal mode are obtained. It is shown, the dispersion equations produce an additional set for the speed of sound (so called second sound) in the fluid. It is concluded, the most general rheological model must include shear-thinning, concentration and second sound phenomena

Determination of Particulate Matters and Total Suspended Particles emitted from Incense Burning

Incense burning is an important ceremonial ritual in Buddhism. It is well recognized that incense smoke has negative health effects, which may be caused by the emission of submicron particles, including ultrafine and nanoparticles. Hence, in this study, the concentration of particulate matter (PM) and total suspended particles (TSP) emitted from incense burning were determined from 4 incense stick brands. The experiment was conducted in a room with a volume of approximately 146m3 using two instruments: an HV sampler and a Nano Sampler. The highest TSPs concentration from long sticks and short sticks were S1 (319.03 μg/m3) and N2 (439.75 μg/m3), respectively. High mass concentration was found in the ultrafine particle range for S2 (112.27 μg/m3) and N2 (117.30 μg/m3). In contrast, S1 and N1 exhibited high concentrations in the coarse particle mode at 79.28 μg/m3 and 86.75 μg/m3, respectively. Out of the 4 incense brands, N2 appeared to have the highest concentration in almost every particle range compared to the other 3 brands. Incense should be burned in a well-ventilated setting and try not to stay in the same place as the altar to reduce the risk of incense smoke exposure.

MODELLING OF A THREE-DISPERSED SUSPENSION FILTRATION

The injection method of soil stabilization is one of the methods to improve the soil base during the road construction. This method consists in the introduction of special compounds into the ground with the help of special equipment. Such compositions, as a rule, are solutions of polymers or cement, which harden, forming a solid base. The advantages of the injection method of soil stabilization for roads include rapid completion of work, minimal environmental impact, the possibility of application in difficult geological conditions, as well as strengthening the soil base at great depth. Injection solutions penetrate into microcracks and micropores of soils, forming a deposition. The study of liquid filtration in a porous soil system is of great practical importance. The paper considers the filtration of liquid in a porous medium with three types of particles. In the considered problem, each of the three types of suspension particles is characterized by its linear filtration function. It determines the size-exclusion particle capture mechanism, in which particles whose diameter exceeds the size of the pores get stuck in them, the rest pass through them unhindered. Numerical solutions are obtained for the concentrations of suspended particles of three types, as well as the total deposition. Depending on the initial parameters of the problem, the concentrations of suspended particles are either monotonic functions or non-monotonic, reaching the maximum value. In this paper, asymptotic solutions are constructed for the concentrations of suspended and retained particles near the concentration front, which are compared with numerical ones. The solution is obtained at infinity using a traveling wave.

Simulation of sandstone formation damage caused by solid particle invasion

During the drilling and completion process, the invasion of solid particles can have a serious impact on reservoir permeability, but there is a lack of effective prediction models for its impact. We developed a prediction model of solid particle invasion damage in response to the issue of reservoir damage induced by solid particle invasion during the exploitation of sandstone reservoirs. By considering the changes in pore permeability characteristics, particle migration and rock stress-strain state are coupled. The findings reveal that as filtration duration increases, the concentration of suspended particles and sediment particles increases, resulting in a progressive reduction in formation permeability around the wellbore. The greater the filtration coefficient, the greater the quantity of particle deposition, however, this also leads to a slowdown in the growth in deposition quantity. As the diffusion rate increases, particles are more likely to deposit. The concentration of suspended particles decreases progressively as tortuosity increases, as does the concentration of sediment particles. Large saturation sedimentation in the pore throat may cause more suspended particles to deposit, lower the effective seepage channel of the pore throat, and drastically impair formation permeability. The results of the impact factor comparison showed that filtration coefficient and medium tortuosity are the key factors. Improving the temporary plugging effect of solid particles in formations with large tortuosity of pore throats can effectively reduce reservoir damage. The findings of this study can help for optimization design of solid particles in drilling fluid for reservoir protection.

Prediction of Clean-room Air-conditioning Defects Using Deep Learning and a Differential Pressure Sensor

A clean room is used for adjusting the concentration of suspended particles using an air-conditioner. It has a fan-filter unit combining a centrifugal fan and a high-efficiency particulate air filter that purifies the outside air and directly affects its cleanliness. Defects in these systems are typically detected using special sensors for each fault, which can be costly. Therefore, this paper proposes a system for diagnosing defects in the fan-filter unit using a single differential sensor and deep learning. The fan-filter unit is part of the air-conditioning system, and it is usually defective in bearings, filters, and motors. These faults include ball wear, internal bearing contamination, filter contamination, and motor speed changes. Each defect was artificially induced in experiments, and the differential pressure data of each defect was learned using a long short-term memory (LSTM) deep learning algorithm. The results of deep learning experiments generated by randomly mixing data five times were presented using a confusion matrix, and the results showed an accuracy of 87.2±2.60%. Therefore, the possibility of diagnosing defects in the fan-filter unit using a single sensor was confirmed.

Virioplankton and virus-induced mortality of prokaryotes in the Kara Sea (Arctic) in summer.

Among the Arctic seas, the largest volume of river runoff (~45% of the total river-water inflow into the Arctic Ocean) enters the Siberian Kara Sea. The viral communities of the Kara Sea are important for the functioning of the marine ecosystem. Studies of virus-prokaryote interactions on the Kara Sea shelf have been conducted only in spring and autumn. Here, we investigated the abundance of free viruses, viruses attached to prokaryotes, and pico-sized detrital particles; the morphology (shape and size) of the viruses, viral infection and virus-mediated mortality of prokaryotes in early summer, i.e., during a seasonal ice melting period and maximum inflow of river-water volumes with high concentrations of dissolved and suspended organic carbon. Seawater samples for microbial analyses were collected across the Kara Sea shelf zone on board the Norilskiy Nickel as a research platform from June 29 to July 15, 2018. Abundances of prokaryotes (range (0.6-25.3) × 105 cells mL-1) and free viruses (range (10-117) × 105 viruses mL-1) were correlated (r = 0.63, p = 0.005) with an average virus: prokaryote ratio of 23.9 ± 5.3. The abundance of free viruses and viral-mediated mortality of prokaryotes were significantly higher in early summer than in early spring and autumn. Free viruses with a capsid diameter of 16-304 nm were recorded in the examined water samples. Waters in the Kara Sea shelf contained high concentrations of suspended organic particles 0.25-4.0 µm in size (range (0.6-25.3) × 105 particles mL-1). The proportions of free viruses, viruses attached to prokaryotes, and viruses attached to pico-sized detrital particles were 89.8 ± 6.0%, 2.2 ± 0.6% and 8.0 ± 1.3%, respectively, of the total virioplankton abundance (on average (61.5 ± 6.2) × 105 viruses mL-1). Viruses smaller than 60 nm clearly dominated at all studied sites. The majority of free viruses were not tailed. We estimated that an average of 1.4% (range 0.4-3.5%) of the prokaryote community was visibly infected by viruses, suggesting that a significant proportion of prokaryotic secondary production, 11.4% on average (range 4.0-34.0%), was lost due to viral lysis. There was a negative correlation between the abundance of pico-sized detrital particles and the frequency of visibly infected prokaryotic cells: r = -0.67, p = 0.0008.

Using deep learning to assess temporal changes of suspended particles in the deep sea

While suspended particles play many important roles in the marine environment, their concentrations are very small in the deep sea, making observation difficult with existing methods: water sampling, optical sensors, and special imaging systems. Methods are needed to fill the lack of environmental baseline data in the deep sea, ones that are inexpensive, quick, and intuitive. In this study we applied object detection using deep learning to evaluate the variability of suspended particle abundance from images taken by a common stationary camera, “Edokko Mark 1”. Images were taken in a deep-sea seamount in the Northwest Pacific Ocean for approximately one month. Using the particles in images as training data, an object detection algorithm YOLOv5 was used to construct a suspended particle detection model. The resulting model successfully detected particles in the image with high accuracy (AP50 > 85% and F1 Score > 82%). Similarly high accuracy for a site not used for model training suggests that model detection accuracy was not dependent on one specific shooting condition. During the observation period, the world’s first cobalt-rich ferromanganese crusts excavation test was conducted, providing an ideal situation to test this model’s ability to measure changes in suspended particle concentrations in the deep sea. The time series showed relatively little variability in particle counts under natural conditions, but there were two turbidity events during/after the excavation, and there was a significant difference in numbers of suspended particles before and after the excavation. These results indicate that this method can be used to examine temporal variations both in small amounts of naturally occurring suspended particles and large abrupt changes such as mining impacts. A notable advantage of this method is that it allows for the possible use of existing imaging data and may be a new option for understanding temporal changes of the deep-sea environment without requiring the time and expense of acquiring new data from the deep sea.

Experimental and numerical investigations of particle suspension suppression mechanisms for a particle-suppression device in a stirred liquid bath

Particle suspension in a turbulent flow can seriously affect the performance of manufactured products in many industrial processes in which the motion of particles cannot be modeled using the numerical method because of the enormous number of particles. Therefore, in this study, a full-scale computational fluid dynamics (CFD) simulation and a 1/5 scaled-down water model experiment were employed to investigate the flow pattern and dynamic behavior of particles in a continuously stirred vessel system. Based on the understanding of the suspension mechanism of settling particles, a particle-suppression device was designed to realize the harmless movement and deposition of particles. The results showed that the flow guidance and division mechanisms of the particle-suppression device led to the inhibition of particle suspensions. In addition, the optimal parameter combination for the device from the water model experiment combined with the orthogonal experimental design, resulted in a 98.3% reduction in the concentration of suspended particles. The suspension of particles was effectively suppressed, which improves product quality and production efficiency. Reliable results can be achieved by combining CFD simulations and water model experiments.

Particle size distribution measurements of widely distributed carbonyl iron powder particles in concentrated suspensions using ultrasonic attenuation

In this paper, particle size distribution (PSD) of widely distributed carbonyl iron powder (CIP) particles in concentrated suspensions was measured using the ultrasonic attenuation technology to analyze their dispersion behaviors. Importantly, their zeta potential was measured using electroacoustic technology. Both visco-inertial and scattering mechanisms were considered while measuring the PSD of these particles with primary sizes ranging from about 100 nm to 10 μm. As a result, the opposite evolution of the PSD curves was observed for nanoscale particles and microparticles, namely, d 01 increased and d 99 decreased when the concentration increased from 15 wt% to 35 wt%, whereas the trend was reversed when the concentration increased from 35 wt% to 75 wt%. This outcome means that changes in concentration cause small and large particles to have opposite dispersion behaviors. The zeta potential of the particles was negative, with absolute values not higher than 22 mV, whereas particle concentration and carrier liquids exerted some effects. This opposite evolution was found first while measuring PSD in concentrated suspensions, where non-Derjaguin, Landau, Verwey, and Overbeek interactions could markedly influence the dispersion behaviors of the widely distributed CIP particles. These results might bring forward some challenges to disperse these particles fully for some advanced applications.

Characterizing a Year-Round Particulate Matter Concentration and Variation under Different Environmental Controls in a Naturally Ventilated Dairy Barn

A mixing fan and spraying system is commonly used to control the indoor environment of naturally ventilated dairy barns worldwide. However, its impact on particulate matter (PM) concentration and variation is still unclear due to the lack of year-round field data. To systematically characterize the PM dynamics under different environmental controls (namely, EC1: No Fans and No Spraying; EC2: Fans; EC3: Fans and Spraying), a year-round continuous monitoring of PM less than 2.5 μm in aerodynamic diameter (PM2.5) and total suspended particle (TSP) concentrations, as well as indoor environmental factors, was carried out inside a naturally ventilated dairy barn using an IoT-based sensor monitoring network. Results showed that the hourly mean TSP and PM2.5 concentrations were 94.7 μg m−3 and 49.8 μg m−3, respectively. EC2 had a higher TSP content (116.6 μg m−3) than EC1 (98.0 μg m−3) and EC3 (81.9 μg m−3). EC1 had the greatest PM2.5 concentration (57.1 μg m−3), followed by EC2 (48.3 μg m−3) and EC3 (44.7 μg m−3). EC1 showed clear TSP and PM2.5 fluctuations during the daily operations at 07:00 to 08:00 and 18:00 to 19:00, while irregular peaks in EC2 and a relatively steady diurnal variation in EC3 were found. Daily Tsp concentrations in the three ECs did not exceed 300 μg m−3. However, 17.8%, 11.5%, and 4.8% of the observed days in EC1, EC2, and EC3 had daily mean PM2.5 concentrations above the healthy threshold (75 μg m−3), mostly from 07:00 to 08:00 and 22:00–07:00. In conclusion, the mixing fan and spraying system had significant effects on PM concentration and variation, and more protection procedures should be taken for farm workers to prevent long-term health risk exposure, to EC1 in particular.

Simulation study on clogging of suspended particles in in-situ leaching of uranium at different concentrations and flow velocity

Clogging problem has become one of the key problems restricting the mining efficiency of in-situ leaching of uranium, and the related research on the law and mechanism of physical clogging has not been reported. In order to identify and understand the complicated law and mechanism, experimental device is established to simulate the physical clogging caused by suspended particles in the uranium process, the physical clogging law and mechanism under different concentrations and velocity of flow are studied. The experimental results show that with the concentration of suspended particles increasing from 100, 200, 300 to 400 mg/L, the permeability of porous media gradually decreases, and the clogging phenomenon becomes more and more obvious. When the size of suspended particles is small and the velocity is 15 mL/min, the porous medium will not appear clogging, while the velocity is 25mL/min, the whole porous medium will slowly appear internal deposition clogging. When the size of suspended solids is larger and the flow rate is 9, 12, 15mL/min, the higher the velocity, the faster the clogging will be, and backwash can alleviate the surface clogging but cannot change the final clogging result. According to the experiment and actual situation, the physical clogging in in-situ leaching of uranium is mainly surface clogging and filter clogging.

Effects of suspended particles in the Jinjiang River Estuary on the physiological and biochemical characteristics of Microcystis flos-aquae.

The effects of different concentrations (100, 150, 200, 250mg/L) and different particle sizes (0-75μm, 75-120μm, 120-150μm, 150-500μm) on the soluble protein content, superoxide dismutase (SOD) and catalase (CAT) activity, malondialdehyde (MDA) content, chlorophyll a (Chla) content, and photosynthetic parameters of Microcystis flos-aquae were studied, and the mechanism of the effect of suspended particulate matter on the physiology and biochemistry of Microcystis flos-aquae was discussed. The results showed that the soluble protein content of Microcystis flos-aquae did not change noticeably after being stressed by suspended particles of different concentrations/diameters. The SOD activity of Microcystis flos-aquae first increased and then decreased with increasing suspended particulate matter concentrations. The SOD activity of Microcystis flos-aquae reached 28.03 U/mL when the concentration of suspended particulate matter was 100mg/L. The CAT activity of Microcystis flos-aquae increased with increasing concentrations of suspended particles and reached a maximum value of 12.45 U/mg prot in the 250mg/L concentration group, showing a certain dose effect. Small particles had a more significant effect on SOD, CAT, and MDA in Microcystis flos-aquae than large particles. The larger the concentration was and the smaller the particle size was, the stronger the attenuation of light and the lower the content of Chla. Both the maximum quantum yield of PSII (Fv/Fm) and the potential photosynthetic activity of PSII (Fv/F0) of Microcystis flos-aquae increased at first and then decreased under different concentrations/sizes of suspended particles. The relative electron transfer rate gradually returned to a normal level over time. There was no significant difference in the initial slope (α) value between the treatment group and the control group, and the maximum photo synthetic rate (ETRmax) and the semilight saturation (Ik) decreased.

Air quality and the health of Norilsk population: dynamics of the situation over 20 years

The article presents a retrospective analysis of the dynamics of air pollution in Norilsk with emissions from the largest metallurgical enterprise MMC Norilsk Nickel. In the city, for many years, elevated concentrations of sulfur dioxide, suspended particles, nickel, copper, benzo(a) pyrene and other substances have been recorded. Their impact has led to increased morbidity and mortality among the population of Norilsk. Estimated health risks from exposure to fine particulate matter (PM10) and sulfur dioxide are given. The excess mortality of Norilsk residents from exposure to sulfur dioxide decreased from 10% in 2007 to 0.8% in 2014—2019.Dynamics of mortality in Norilsk for 2008—2019 compared with data on the urban population of the Krasnoyarsk Territory is ambiguous. The mortality of men from all causes, including cerebrovascular and circulatory system diseases, is lower than in other cities of the Krasnoyarsk Territory, but higher from respiratory diseases. Mortality among women in Norilsk is higher than in the urban population of the Krasnoyarsk Territory by 16.6%, incl. from diseases of the respiratory system — by 82.7%, from diseases of the circulatory system — by 6.5%. The higher mortality rate of the female population of Norilsk among other cities of the Krasnoyarsk Territory may indicate the detrimental effects of the impact of polluted atmospheric air on the female part of the population.

Tribological variable-friction coefficient models for the simulation of dense suspensions of rough polydisperse particles

The rheology of concentrated suspensions of particles is complex and typically exhibits a shear-thickening behavior in the case of repulsive interactions. Despite the recent interest arisen, the causes of the shear-thickening remain unclear. Frictional contacts have been able to explain the discontinuous shear thickening in simulations. However, the interparticle friction coefficient is considered to be constant in most simulations and theoretical works reported to date despite the fact that tribological experiments demonstrate that the friction coefficient can not only be constant (boundary regime) but also decrease (mixed regime) or even increase (full-film lubrication regime), depending on the normal force and the relative velocity between the particles and the interstitial liquid between them. Interestingly, the transition between the boundary regime and the full-lubrication regime is governed by the particle average roughness. Particle-level simulations of suspensions of hard spheres were carried out using short-range lubrication and roughness-dependent frictional forces describing the full Stribeck curve. Suspensions with different particle’s roughness were simulated to show that the particle roughness is a key factor in the shear-thickening behavior; for sufficiently rough particles, the suspension exhibits a remarkable shear-thickening, while for sufficiently smooth particles, the discontinuous shear-thickening disappears.

Ensuring normal air quality in office premises with the existing ventilation system

In the conditions of growing interest in indoor air cleaning and strengthening WHO recommendations regarding the concentration of suspended particles in the air (should not exceed 5 μg/m3), there is a need to create clear rules for placing cleaning equipment on ventilation and air conditioning systems. This applies not only to objects that are just being designed, but also to already operated objects with a functioning ventilation system. After all, it is precisely at such objects that there are limited opportunities to intervene in the work of not only engineering systems, but also the operation of the building itself during repairs. The goals of the study were to obtain data on the efficiency of air purification in a given volume with the available air exchange rate of a functioning supply-exhaust system. A separate task was to check the data declared by the manufacturer regarding the pressure drop on the built-in HERA channel filter. The most effective way to clean indoor air from pollutants is considered to be its removal from places of permanent residence of people. Using a general exchange ventilation system equipped with modern filtering equipment, you can achieve significant results in improving air quality. In this case, the ventilation system in an office building in the city center is considered, which was equipped with an additional channel filter with a MERV16 (or HEPA 11) class filter cassette. This modernization of the ventilation system in half a year of operation made it possible to reduce pollution with particles in the size range of 0.3-10 microns in the air environment of office premises by 70...76 % with an insignificant multiplicity in compliance with the norms of the minimum value of air exchange in terms of the amount of fresh air according to the sanitary norm and allowed to avoid significant capital investments for the repair of engineering networks and losses due to the impossibility of operating the building during the repair. The conclusions of the study need to be checked in office premises with an existing ventilation system when recording a gradual decrease in the concentration of pollutants in the premises during the operation of the system in order to determine the optimal multiplicity to achieve the specified air quality when using filters.

The impact of heavy metals that released from vehicles exhausts on some biochemical parameters in Eucalyptus and Ziziphus plants in street intersections of Baghdad city

The air pollution by vehicles exhaust is consider the most risk environmental problems, especially when precipitate on soil surface and transport to the plants and entering the food chain. so that, the current study was carried out to determine the impacts of air pollution on the plants growth in traffic intersections, the study was carried out in Baghdad city, identified two regions for each of the both sides of the Rusafa and Karkh by two main sites for each region, as well as, the secondary stations in each site. the heavy metals and total suspended particles concentrations were determined in the filter paper that suffer the pollution air for 30 min. in specific sites using sniffer device. The concentrations decrease of some pollutants was noticed more than to the national and global permitted limits and the summer was the highest season in pollution during study period. Eucalyptus and Ziziphus spina Christi plants was chosen to evaluating the impacts of pollution on the plants because its being of the most common and the evergreen trees in the Baghdad s' streets. Primary metabolites content in plants was measured as total chlorophyll recorded a height concentration in August(98.631mg/gm) in Eucalyptus leaves ,while the total protein content reached to maximum concentration (26.101 mg/gm) in both plants, either total carbohydrate content reached to (88ppm) in Eucalyptus leaves and (74.62ppm) in Ziziphus leaves and noticed that , the increase in concentration of pollutants affected on the protein and carbohydrate content. Seven phenolic compounds was diagnosed being one of the main secondary compounds of metabolism , the increase in total phenolic content was recorded in the region that have a high concentration of carbon dioxide was reach to (6699.88ppm) in Al-Mansour(3) samples compared to the control samples was(2388.87ppm). the heavy metals concentrations in the leaves of eucalyptus and ziziphus arranged from more to less as steady regime throughout the study period in the following order: iron > zinc > copper > lead .

Yield stresses of concentrated suspensions of rigid particles in the volume fraction range of 0.62 to 0.78 via steady torsional flow

Yield stresses of concentrated suspensions of rigid particles in the volume fraction range of 0.62 to 0.78 via steady torsional flow

HY-1C/D CZI Image Atmospheric Correction and Quantifying Suspended Particulate Matter

HY-1C/D both carry a coastal zone imager (CZI) with a spatial resolution of 50 m and a swath width of 950 km, two observations can be achieved in three days when two satellites operating in a network. Accurate atmospheric correction is the basis for quantitative inversion of ocean color parameters using CZI However, atmospheric correction in estuarine and coastal waters with complex optical properties is a challenge due to the band setting of CZI. This paper proposed a novel atmospheric correction algorithm for CZI images applicable to turbid waters in estuarine and coastal zone. The Rayleigh scattering reflectance of CZI was calculated based on a vector radiative transfer model. Next, a semi-empirical radiative transfer model with suspended particle concentration as the parameter is used to model the water-atmosphere coupling. Finally, the parameters of the coupling model are solved by combining a global optimization method based on a genetic algorithm. The results indicate that the CZI-derived remote-sensing reflectance (Rrs) are in good agreement with the quasi-synchronous Landsat-8/9 operational land imager (OLI) derived Rrs in the green and red bands (R2 > 0.96). Validation using in situ data revealed that the RMSE of the CZI-derived Rrs in the green and red bands was 0.0036 sr−1 and 0.0035 sr−1. More importantly, the values and spatial distributions of suspended particulate matter (SPM) estimated by CZI and those estimated by OLI in the Subei Shoal and the Yangtze River Estuary are basically consistent, and the validation using in situ data revealed that the inversion of SPM concentration by CZI was effective (R2 = 0.86, RMSE = 0.0362 g/L), indicating that CZI has great potential and broad application prospects for monitoring the spatial and temporal dynamics of SPM in estuarine and coastal waters. The study results will lay the foundation for further estimating suspended sediment fluxes and carbon fluxes, thus providing data support and scientific basis for promoting resource development, utilization and conservation strategies in estuarine and coastal areas.

Operational parameters impact on spatial and temporal distribution and multifractal characteristics of particulate matter concentration under the sink effect

The influences of different factors on spatial and temporal mass transfer mechanism and dynamic characteristics of particulate matter (PM) under the sink effect are not clear. The objective of this study was to quantitatively analyze the influences of operational parameters on spatial and temporal distribution and multifractal characteristics of indoor suspended PM concentration under the sink effect. Results showed that with the increase of the applied voltage of the purification device, the reverse increase processes of PM1 and PM2.5 concentrations were progressively attenuated, and PM10 and total suspended particulates (TSP) concentrations decreased clearly. The dynamic evolution processes of the PM concentration series all presented strong persistence and obeyed the scale-invariant power-law statistical distributions. The positive correlation of the PM concentration series between five distances increased with the increase of applied voltage. This study can provide a reference basis for further refining the PM purification theory system under the sink effect.

Suspended particles concentrations in the secondary schools in Bor (Serbia) in heating season

This paper presents the results of measurements the suspended particles of the PM 10 and PM 2.5 fractions in two high schools in Bor (School of Mechanical and Electrical Engineering-MS and Grammar School-GM). The measurements were conducted in two heating seasons for a duration of seven days (five weekdays, and two weekend days). Periods during the weekdays when there were classes and weekend days when there were no classes at school were analyzed separately. The measurement results show that the average concentrations of suspended particles PM 10 during the class period were 1.7 (GM) and 2.4 (MS) times higher than in the period without classes. The average concentrations of suspended particles PM 2.5 in both schools during the class period were 1.5 times higher than in the period without classes. In MS the average PM 10 and PM 2.5 concentrations during classes were above daily limit values for 3 of 5 working days. In contrast, there was no exceeding of the average daily limit values for concentrations of suspended particles during classes in GM. The results of measurements indicate that more attention should be paid to the way classrooms are cleaned to reduce the possibility of particles resuspension due to the movement of pupils during the teaching period.