Concentration Of Suspended Particles Research Articles

Suppression of Intense Fluid Oscillations by a Floating Particle Layer

The results of the experiments on the influence of a positive-buoyancy-particle layer on the process of breaking and regularization of the standing gravity Faraday wave on free water surface in a rectangular vessel are discussed. The effect of increase in the particle layer thickness on the limit steepness of the regular wave and its dissipative properties is considered. It is shown that the use of highly concentrated polystyrene particle suspension as the upper layer modifies significantly the barotropic wave mode dynamics and ensures regularization of the waves with total suppression of their breaking mechanisms.

A study of atmospheric pollutants (particulates, metallic elements) at an agricultural site

In this study, the total suspended particulate (TSP) concentrations and dry deposition of ambient air particulates are measured using a high-volume air sampler and a dry deposition plate at an agricultural sampling site in central Taiwan from March of 2019 to February of 2020. In addition, the concentrations of metallic elements attached to the particulates and dry deposits are analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Finally, the TSP and metallic elements concentrations in TSP at different sampling sites around the world are also compared and discussed. The results indicated that the average highest TSP concentrations and dry depositions values both occurred in autumn, and the agricultural sampling site had the average greatest ambient air particulates dry depositions velocities when compared with other previous characteristic-related studies in Taiwan. In addition, metallic element Al had the average highest concentrations and dry depositions and metallic element Cd had the average lowest concentrations and dry depositions values in this study. In addition, metallic elements Cr, Cu, Pb, and Zn had the average highest concentrations when compared with other typical sampling site studies (airport, suburban, downtown, residential, industrial, and wetlands) in central Taiwan. Furthermore, when compared with the other previous metallic elements concentrations found in related studies in other regions from 1978 to 2020, the results obtained in this study indicated that the average metallic element concentrations Cr, Cu, Pb, and Zn in Taiwan were only lower than those reported in India and China. Taiping District is the main fruits production area in central Taiwan. Therefore, continued monitoring of ambient air related pollutants and finding the possible pollution sources have become an important issue for this agricultural site. From the above analysis, we also conclude that ambient air particulates and all the metallic elements dry deposition values obtained in this study were higher than those from the other characteristic sampling sites where studies were previously conducted in Taiwan.

Trace metals at the tree-litter-soil- interface in Brazilian Atlantic Forest plots surrounded by sources of air pollution.

Passive biomonitoring was applied in four Atlantic forest plots in southeast Brazil, affected by different levels of trace metal pollution (OP site located in Minas Gerais State and PEFI, PP and STG located in São Paulo State). Native tree species were selected as biomonitors according to their abundance in each plot and successional classification. Current trace metal concentrations in total suspended particles, leaves of non-pioneer (NPi) and pioneer (Pi) species, topsoil (0-20cm) and litter and concentration ratios at the plant/soil interface were analyzed to verify the atmosphere-plant-soil interactions, basal concentrations, spatial variations and metal accumulation at the ecosystem level. Redundant analysis helped to identify similar characteristics of metal concentrations in PP and PEFI, which can be influenced by the high concentrations of elements related to anthropogenic inputs. Analysis of variance and multivariate statistics indicated that the trees of OP presented higher concentrations of Cr, Fe, Mn and Ni than those in the other sites. High enrichment of Cd, Fe, Ni in non-pioneer plants indicated that the PP forest (initially considered as the least polluted) has still been affected by metal pollution. Soil collected in STG was enriched by all elements, however these elements were low available for plant uptake. Metal deposited in leaves and litter was an important sink for soil cycling, nevertheless, these metals are not bioavailable in most cases. Non-pioneer tree species revealed to be more appropriate than pioneer species to indicate the current panorama of the contamination and bioavailability levels of trace metals in the tree community-litter-soil interface of the Atlantic forest remnants included in this study.

Research on in-situ observation system of seabed boundary layer based on self-potential measurement

The submarine boundary layer is a dynamically changing strip located near the seabed interface. The dynamic change process involves the resuspension and redeposition of sediments, which has an important impact on the transportation of seafloor sediments and the transport of offshore chemical substances. Based on the self-developed self-potential monitoring device, the stability of the device and the characteristics of the seabed and the bottom layer of the sea floor with different textures were tested through laboratory experiments. The results show that the self-developed self-potential monitoring probe has high corrosion resistance, good electrode stability, and guaranteed measurement accuracy. The self-potential measurement can clearly identify the position of the seabed interface, and can judge seabed sediments by positive and negative anomalies. Nature, the sandy seabed is negative anomaly (about -8 mv), the clayey seabed is positive anomaly (about 10 mv). The concentration of solid suspended particles in the seawater and the self-potential difference between the seawater and the seabed appear relatively good linear relationship, the smaller the difference, the greater the concentration of solid suspended particles. The re-deposited sediment changes its self-potential under the influence of material composition and pore structure, but this effect gradually decreases as the consolidation time increases. Therefore, the spontaneous potential measurement can better reflect the dynamic changes of the seafloor sediments, and effectively monitor the dynamic changes of the seafloor boundary layer. It provides a new method for the in-situ observation of the dynamic changes of the submarine boundary layer.

Improving the design of a downhole filter for fluid production with an increased concentration of suspended particles

The reliability of the underground equipment of a well sucker rod pump installation will be improved by the use of a new sand filter design, the principle of which is based on the use of centrifugal force of a moving reservoir fluid. To determine the subtlety of cleaning the reservoir fluid from mechanical particles, it should be considered that the fluid velocity is the same as the particle velocity. To do this, we use the universal expression by analogy to our case for the stream function. To develop a specific filter (determination of structural dimensions) taking into account the well conditions, nomograms are developed taking into account all technical and technological conditions. The main advantage of the developed sand filter over other designs is the ability to pass formation fluid even when the cavity for collecting sand and the space between the filter housing and the pipe with radial channels are filled. The presence of the latter also does not affect the performance of the sucker rod pump, in the absence of jamming of the plunger in the cylinder.

Tunable discontinuous shear thickening in capillary flow of MR suspensions

Very concentrated suspensions of iron particles in water or ethylene glycol can be obtained thanks to the use of superplasticizer molecules used in cement industry. At high volume fractions, these suspensions show a discontinuous shear thickening which was thoroughly characterized in rotational geometries. We will show that the jamming transition is also present in a capillary flow, and that it manifests through the formation of a non-consolidated porous medium at the constriction between the barrel and the capillary. In suspension of iron particles, the dynamics of formation of this porous medium, and so the pressure, can be controlled by a low magnetic field and is reversible for a constant volume flow rate, opening potential new applications in the domain of dampers and force control devices.

Implications of phosphorus partitioning at the suspended particle-water interface for lake eutrophication in China’s largest freshwater lake, Poyang Lake

Nutrient partition, especially for phosphorus (P), has been prominently changed that was caused by variation of river-lake relationship during the post-Three Gorges Reservoir and catchment alternations. Changes in proportion of total particulate phosphorus (TPP) and total dissolved phosphorus (TDP) might accelerate lake eutrophication, but limited attention has been paid to P partition over suspended particle (SP) levels. Data analysis showed that SP concentration presented a positive effect on TPP in wet season and soluble reactive phosphorus (SRP) in dry season, indicating seasonal physical and chemical variations. Based on this phenomenon, we proposed a hypothesis that the SP levels would affect TDP and TPP proportions by partition in aqueous-solid. It was found that using the parabola models to fit the sorption relationships of SRP and TDP (R2 > 0.6, p < 0.01), the maximum sorption capacity (Qmax) was 64.54 mg/kg and 60.52 mg/kg at 400 mg/L of SP level, respectively. In addition, the partition coefficients (KP) of TDP and SRP were logarithmically increased with SP levels, indicating that higher SP levels (>400 mg/L) would hinder the sorption process. Furthermore, enhancing turbulence lead to less sorption of SRP and TDP at high SP levels (>800 mg/L). The sorption of SRP and TDP related to the presence of Fe/Al oxy-hydroxides were enriched in the Fe/Al–P fraction (47% of TP). The findings of this study indicated that the low SP levels would increase P bioavailability for alga and is not conducive for lake eutrophication management.

Propagation, deposition, and suspension characteristics of constant-volume particle-driven gravity currents

In this laboratory study, propagation behaviour, particle deposition patterns, and suspension characteristics of non-cohesive particle-driven gravity currents formed under constant-volume release conditions were investigated. The experimental gravity currents were created in a two-dimensional lock exchange type tank using two different particles (silicon carbide and glass beads) with four different median diameters. Video imaging and image processing techniques were utilized to monitor the current propagation, laser diffraction size analysis and dry weighing techniques were utilized to examine the size and mass characteristics of the deposits and suspensions, and acoustic Doppler velocimetry was utilized for flow velocity measurements for turbulence analysis. Our observations showed that the experimental gravity currents experienced two different propagation phases based upon the particle settling regimes. The first propagation phase was named as the propagation with the turbulence-dominated settling (TDS) and the later propagation phase was named as the propagation with gravity-dominated settling (GDS). It is found that a critical turbulent Reynolds number value (estimated to be O(1)) delineates the settling regimes, hence determines the transition between the propagation phases. With increasing particle settling velocity, the observed propagation phases in our experimental currents showed increasing deviations from the slumping, inertia-buoyancy, and viscous–buoyancy propagation phases that have been reported for homogeneous constant-volume gravity currents with no or negligible settling in the literature. Propagation observations showed that the initial median particle diameters of the currents have negligible effect on the current propagation characteristics during the TDS phase, but become important during the GDS phase. The currents with smaller initial median particle diameters propagated faster and a longer distance in the GDS phase than their counterparts with larger median particle diameters. The deposited particle characteristics indicated that particles of different sizes settle at similar speeds during the TDS phase due to turbulent mixing and the settling speed becomes dependent on the particle size during the GDS phase. As a result, size sorting of the deposited particles became more pronounced during the GDS phase. At the earlier stages of propagation, the vertical profiles of suspended particle concentrations in the current head showed some extent of vertical uniformity due to turbulent mixing around the half height of the current head. On the other hand, at the later stages of propagation, suspended particle concentration profiles exhibited an exponential profile. Deposited and suspended particle characteristics showed that horizontal particle sorting, that is size grading of particles in the flow direction, was more pronounced than the vertical particle sorting, that is size grading of particles at different elevations within the current head.

Field Measurement of Spatiotemporal Algae Distribution Using In Situ Optical Particle Size Sensor

AbstractMany environmental problems have arisen due to algae since the large‐scale river projects were implemented in Korea. Therefore, it is imperative to monitor algal distribution status in order to find a solution to these problems. Sporadic sampling and population estimation by microscopy are traditional algae monitoring methods. However, these techniques yield spatiotemporally limited information. In order to overcome these weaknesses, the present study aimed to investigate the applicability of a new monitoring technique using an in situ optical particle sizer (LISST‐100X) for algal size and distribution estimation. The survey site was the mountain range where the Nakdong River and Nam River converge. The number of algal populations and dominant species were identified, and suspended particle concentrations and distribution were surveyed based on hydraulic characteristics, water quality, and water sampling. Field monitoring data were also collected using a unmanned aerial vehicle (UAV) in order to assess the applicability of the algal distribution estimation method using an in situ optical particle sizer for natural streams. At the time of the algae outbreak, relatively large‐sized suspended particles are distributed throughout the surface layer, which is distinguished from the similar distribution in the general water bodies. Because of these characteristics, it was possible to investigate vertical and spatial algae distribution. Additionally, the mixing pattern was analyzed according to pulsed flow in order to estimate the applicability of monitoring algal bloom removal according to discharge.

Viscoelasticity and the dynamics of concentrated particle suspension in channel flow

Abstract

Correlación entre diferentes contaminantes atmosféricos de la Ciudad de México y el Área Metropolitana

Se lleva a cabo un estudio de correlación estadística entre datos numéricos correspondientes a la concentración de las partículas suspendidas y a la concentración de gases contaminantes que son obtenidos de las mediciones registradas en la base de datos de la Red Automática de Monitoreo Atmosférico (RAMA) para la Ciudad de México y el Área Metropolitana. Se reporta una importante dependencia entre los pares de gases NO2-NOX, NO-NOX, CO-NO, CO-NOX y los pares de partículas PM2.5-PM10, PMCO-PM10 cuando el estudio se realiza tomando como referencia una sola estación de monitoreo. Por otra parte, se encuentra una estrecha relación entre el ozono (O3) de una estación con el de otra para diferentes pares de estaciones.

Can the hydrophobic organic contaminants in the filtrate passing through 0.45 μm filter membranes reflect the water quality?

In the traditional water quality assessment, the concentration of total dissolved hydrophobic organic compounds (HOCs) passing through 0.45 μm filter membranes is usually used to evaluate the influence of HOCs on water quality. However, the bioavailability of dissolved organic matter (DOM)-associated and particle-associated HOCs is not considered. In the present work, pyrene, fulvic acid, and natural suspended particles (SPS) were used to simulate natural water (raw water). The immobilization and pyrene content in the tissues of D. magna caused by total pyrene in the raw water and those caused by freely dissolved pyrene with the concentration equal to the total dissolved pyrene in the filtrate of raw water were compared to determine whether the total dissolved pyrene concentration can reflect the water quality. The results indicated that when the DOM concentration was 5 mg C L−1 and the SPS concentration was higher than 0.2–0.4 g L−1, the bioavailability of pyrene was underestimated by the traditional water quality assessment because of the SPS-associated pyrene, and it was underestimated by 23.6–63.9% when SPS concentration was higher than 0.6 g L−1 due to the neglection of SPS-associated pyrene. Furthermore, the threshold value of SPS concentration was related to the SPS size and composition, and the effects of SPS and DOM on water quality were influenced by the concentration, size, and composition of SPS as well as the molecular weight of DOM. This study suggests that the traditional water quality assessment should be improved by comprehensively considering concentrations and characteristics of SPS and DOM.

Two models for determination of the effective conductivity of concentrated suspensions of ellipsoidal particles with surface phenomena

Many multicomponent materials such as rocks or nanofluids are characterized by the presence of conductive surface layers at the interface. These conductive layers can change effective physical properties (for example, effective thermal or electrical conductivities) of such materials. A suspension of ellipsoidal particles with surface conductivity is considered. Two theoretical models are presented for the solution of the so-called one-particle problem that can be used then in any homogenization scheme for determination of the effective conductivity of such suspension. The first model is based on the modification of the boundary conditions for the electric current density (the jump boundary conditions). The second model is based on the confocal ellipsoids. The effect of surface conductivity is obtained for this model by limiting transition to the infinitely thin external ellipsoidal shell.For the calculation of the effective conductivity of the medium containing the ellipsoidal particles with the surface phenomena one of the popular homogenization scheme named by Differential Effective Medium (DEM) method is used. Comparison of numerical results obtained by this method for two different solution of the one-particle problem show that these results are rather close even for very large values of the surface conductivity.

Size‐Fractionated Compositions of Marine Suspended Particles in the Western Arctic Ocean: Lateral and Vertical Sources

AbstractWe present full water depth sections of size‐fractionated (1–51 μm; &gt;51 μm) concentrations of suspended particulate matter and major particle phase composition (particulate organic matter [POM], including its carbon isotopic composition [POC‐δ13C] and C:N ratio, calcium carbonate [CaCO3], opal, lithogenic particles, and iron and manganese [oxyhydr]oxides) from the U.S. GEOTRACES Arctic Cruise (GN01) in the western Arctic in 2015. Whereas biogenic particles (POM and opal) dominate the upper 1,000 m, lithogenic particles are the most abundant particle type at depth. Minor phases such as manganese (Mn) oxides are higher in GN01 than in any other U.S. GEOTRACES cruises so far. Extremely depleted POC‐δ13C, as low as ~ −32‰, is ubiquitous at the surface of the western Arctic Ocean as a result of different growth rates of phytoplankton. Moderate penetration of depleted POC‐δ13C to depth indicates active sinking of large particles in the central basin. Lateral transport from the Chukchi shelf is also of significance in the western Arctic, as is evident from increases in biogenic silica to POC ratios and Mn oxide concentrations in the halocline, as well as lithogenic element contents in the deep waters. Our study supports previous suggestions of the near absence of CaCO3 in the Arctic Basin. This study presents the first data set of concentration and composition of suspended particles in the western Arctic Ocean and sheds new light on the vertical and lateral processes that govern particle distribution in this enclosed ocean basin.

Both microbial abundance and community composition mattered for N2 production rates of the overlying water in one high-elevation river

Overlying water is another potential hotspot of nitrogen removal through anammox and denitrification reactions in river systems. However, N2 production and the controlling factors have rarely been investigated in the overlying water of high-elevation rivers. This study analyzed the abundance and community of denitrifying and anammox bacteria as well as their effects on N2 production rates in the overlying water of the Yellow River source region (elevation range: 2687−4223 m). Higher suspended particle concentrations remarkably promoted functional gene abundances of both denitrifying and anammox bacteria (r > 0.9, p < 0.01). N2 production rates in overlying water samples ranged from 0.25 to 4.22 μmol N2 L−1 d−1. The overlying water was estimated to contribute to 36.8% (on average) of riverine N2 emission flux. Higher temperatures markedly accelerated N2 production rates (p = 0.051). Moreover, N2 production rates were positively related to both anammox and denitrifying bacterial abundances (p < 0.05), and such relationships were markedly affected by corresponding community compositions. The explanatory power of denitrifier abundance (R2 = 0.56) for N2 production rate variations was greatly elevated when it was integrated with community composition (R2 = 0.92). This study highlights the significance of overlying water nitrogen removal in the Yellow River source region; moreover, the effects of both microbial abundance and community composition on riverine N2 production rates should be considered in future research.

A national‐scale study of spatial variability in the relationship between turbidity and suspended sediment concentration and sediment properties

AbstractTurbidity, an index of light side‐scattering, depends on the mass concentration of suspended sediment (SS) within water. Turbidity of river water is regulated by the presence of suspended particulate matter and is used to identify visual changes in response to SS. We used data from the New Zealand National River Water Quality Network, to calculate “specific turbidity” (K; turbidity normalised to mass concentration of suspended particulates). Specific turbidity is shown here to be an effective metric to assess the effect of suspended material composition and particle size distribution of suspended particulate matter over different landscape characteristics, and the effect on SS‐turbidity relationships. Of the catchment characteristics considered in our study, specific turbidity was most responsive to lithological factors, and relatively insensitive to land use and soil parameters. Decreasing particle size has a positive linear response to K, attributed to the higher proportion of ultra‐fine particulate material that is generated by certain lithologies, underscoring the lithological influence on K. SS‐turbidity relationships, therefore, vary spatially across New Zealand's national record of water clarity, and K is considered a useful index for inter‐catchment comparison of SS than turbidity alone.

Comparison of work environment air quality and application of geostatistic technique in the spatial distribution of PM2.5 and PM10 in a number of industrial workshops

Introduction: Air quality in industrial workshops is affected by various harmful chemical agents. Purpose of this study was to compare work environment air quality in a number of industrial workshops based on the mass concentration and number of suspended particles in air and application of Kriging geostatistical method in industries. Materials and Methods: This observational study was carried out in four workshops including cuprous waste separation works, rolling and cutting, casting and copper smelting, manufacturing aluminum products and double-glazed glass production. Using particle mass counter sampler of Tes 5200 model, mass concentration and number concentration of suspended particles in row of different diameters were measured. The spatial distribution map of PM2.5 and PM10 in each of workshops was prepared using Kriging geostatistic method in GIS environment Version 10.5. Results: The highest mass concentration (8.42 mg/m3) and number concentration (445058 Particle/lit in differential mode and 885446 Particle/lit in cumulative mode) were measured in the manufacturing aluminum products workshop. The highest mass concentration and number concentration of suspended particles were obtained for row diameters of 10 µm and 0.5 µm, respectively. Interpretation of Kriging maps showed that various areas of the industries such as radiation furnace, scrap press, aluminum smelter, sieve, diamond machine, glass furnace and ingot molds had the highest frequency of PM2.5 and PM10. Conclusion: Engineering control actions such as installation of ventilation systems in halls and design and installation of a local hood in the entrance sections of the aluminum smelting furnace and sieve in manufacture of aluminum products workshop and copper ingot molds in casting and smelting workshop is essential for improved air quality.

Siliceous sponge expansion and phosphogenesis in a shallow water environment in the Malyi Karatau Range (Kazakhstan) during the Precambrian-Cambrian transition

Ocean oxygenation during the Precambrian-Cambrian transition is thought to be one of the key factors for the rapid diversification of animals, known as the ‘Cambrian Explosion’. Siliceous sponges inhabiting continental slope settings were capable of shifting the respiratory oxygen demand in the water column to depth, resulting in an increase in oxygen levels of shallow water. To assess the global importance of the impact of ecosystem engineering by sponges, we evaluated the palaeo-environmental conditions that confine sponge expansion using multiple geochemical proxies including silicon and carbon stable isotopes as well as major- and trace elements in cherts and siliceous sedimentary rocks that were deposited in shallow water around the Precambrian-Cambrian transition. We investigated three lithosections in the Malyi Karatau Range in southern Kazakhstan. The lowermost chert samples of these sections are typically characterized by comparably low δ30Si values and exhibit molds of siliceous sponge spicules. Upsection the occurrence of cross-bedding structures and granular phosphorites document the shallowing of the depositional environment, where overall increasing δ30Si values and increasing Al/Si indicate less settlement of sponges and higher suspended particle loads. Corresponding carbon isotope records of the carbonate fraction decrease from near-zero to negative carbon isotope values averaging −5.9‰. The δ13Ccarb values overall coincide with Y/Ho, the redox indicator Ce/Ce*, and mass fractions of carbonate fluorapatite, suggesting that these ratios are predominantly controlled by the mineralization of organic matter in phosphatic sediment. The studied sections document the ecological requirements for sponge settlement and proliferation, such as the presence of a hard substrate and sufficiently low suspended particle concentrations and/or low wave energy. This work suggests that the widespread appearance of karsted surfaces around the Precambrian-Cambrian transition that were subsequently submerged during the Cambrian transgression would have created permissive habitats for sponges and large phosphate deposits. The capability of sponges to oxygenate shallow seawater and extensive phosphorous burial in epicontinental basins are thus feasible mechanisms for the seawater oxygenation around the Precambrian-Cambrian transition.

Flow resistance law under suspended sediment laden conditions

The uniform flow resistance equation, in the form due to Manning or Darcy-Weisbach, is widely applied to establish the stage-discharge relationship of a river cross-section. The application of this equation, namely the slope-area method, allows to indirectly measure the corresponding river discharge by measurements of bed slope, water level, cross-section area, wetted perimeter and an estimate of channel roughness. In this paper, a recently deduced flow resistance equation for open channel flow was tested during conditions of suspended sediment-laden flow. First, the flow resistance equation was determined by dimensional analysis and by applying the condition of incomplete self-similarity for the flow velocity profile. Then the analysis was developed by the following steps: (i) for sediment-laden flows characterized by known values of mean diameter and concentration of suspended sediments, a relationship (Eq. (28)) between the Γ function of the velocity profile, the channel slope and the Froude number was calibrated by the available measurements; and (ii) a relationship for estimating the Γ function (Eq. (29)) which also takes into account the mean concentration of suspended particles was also established. The theoretical flow resistance law (Eq. (26)) coupled with the relationship for estimating the Γ function (Eq. (28) or Eq. (29)), which is characterized by the applicability of a wide range of flow conditions, allowed to estimate the Darcy-Weisbach friction factor for flows with suspended-load. The analysis showed that for large-size mixtures the Darcy-Weisbach friction factor can be accurately estimated neglecting the effect of mean concentration of suspended sediments while for small-size mixtures the friction factor decreases when the mean sediment concentration increases.

Potential Chemical Stressors Emitted During the Operation of Machines in the Digital Printing Process

ABSTRACT The digital printing process contributes to the quality of indoor air through the emission of chemical stressors such as total volatile organic compounds (TVOCs) and suspended particulate matter (SPM). The concentration levels of SPM and TVOCs were determined using the gravimetric and gas chromatography method, respectively. The results show that the digital printing machines and the cutting machine do not produce PM2.5 particles. The significant cumulative mass concentrations of PM10 suspended particles of 9.91 μg/m3 for a single-colour digital printing machine, 4.45 μg/m3 for a four-colour digital printing machine, and 2.02 μg/m3 for a cutting machine, were detected. By comparing the cumulative values of TVOC concentration levels measured, it can be concluded that the values have been 4 to 12 times higher for the four-colour digital printing machine than for the single-colour digital printing machine. Namely, the TVOC concentration levels measured for the four-colour digital printing machine ranged from 28.69 to 57.30 mg/m3, while the values for the single-colour digital printing machine ranged from 2.31 to 13.51 mg/m3. Considering the fact that there are no standards of quality of indoor air in printing offices defined in the Republic of Serbia, the results obtained could represent a valid basis and a worthy guideline for the definition of values necessary for the indoor air quality assessment.