Indoor Particle Research Articles

Analysis of vertical movement of particulate matter due to the stack effect in high-rise buildings

Outdoor particulate matters (PM) enter the indoors with airflow due to wind pressure, temperature differences, and variable pressures from HVAC systems. PM introduced into the indoor space is deposited on the surface according to the indoor environmental conditions to reduce the indoor particle concentration. In particular, in high-rise buildings in winter, the stack-induced driving force, which is a function of the height of the building and the temperature difference between indoor and outdoor, is dominant. High-rise buildings have vertical pathways for the transport of PM between floors within the building, and eventually distribute it to households.This study aims to analyze the characteristics of PM transport in the vertical shaft in a high-rise building, and to propose a method to calculate penetration and deposition properties to predict indoor particle concentration. An optimization method was proposed to calibrate the multi-zone airflow and particle transport model using field measurement, multi-zone airflow/contaminant simulation, and genetic algorithm (GA)-based optimization techniques. The target building was a 43-story high-rise residential building, and CONTAM was used for multi-zone simulation. The results showed that the PM concentration in the vertical shaft decreased toward the upper floors due to wall deposition. The deposition rate in the vertical shaft was calculated to be less than 0.3 h−1, was the smallest at the Neutral Plane Level (NPL), and increased toward the upper and lower floors. In other words, the deposition rate in vertical space was inversely proportional to the airflow rate. The deposition rate of the vertical shaft was calculated to be smaller than that of the horizontal space. The reliability of the PM concentration prediction results calculated using the proposed method in this study was valid, and satisfied ASTM D5157.

Ultrafine particles: A review about their health effects, presence, generation, and measurement in indoor environments

Human exposure to aerosols has been associated with diseases and death, reducing the population's life expectancy up to a few years. Indoor particulate matter is predominant in determining human exposure to PM because people spend most of their time indoors.Ultrafine particles (UFP) impact the human body differently from PM2.5 or PM10 fractions. Therefore, scientists cannot apply the same approach to assess the effects of UFP and PM on human health.This work summarizes the health effects, generation, and measurement of ultrafine particles in indoor environments through a literature review. When indoor particle generation is low, particle concentration indoors depends strongly on outdoor aerosols, with an indoor-to-outdoor ratio below 1. In buildings with a high indoor particle generation, the average indoor-to-outdoor UFP concentration ratio can reach 14. Combustion, electric heating, and house cleaning are the main generators of UFP indoors.Current standards for UFP assessments do not provide a solid ground for accurate and reliable measurements. Moreover, the lowest detection limit of instruments used to measure UFP concentration can be significantly different while also showing poor repeatability even among instruments with the same manufacturer and model. Consequently, data supplied by studies on UFP health effects are insufficient and inconclusive.Using ultrafine portable monitors would allow determining properly human exposure to PM0.1, but such instruments are expensive for wide use. Since there is a good correlation between UFP and NOX data, low-cost NOX sensors are good candidates to create a dense and accurate monitoring network of UFP, including indoor environments.

Integrated effects of the heat recovery ventilation and heat source on decay rate of indoor airborne particles: A comparative study

Given the high concentration of indoor airborne particles during the winter and their harmful effects on human health, it is of great importance to examine combined effects of the ventilation and heat source on indoor particle dispersion. The present study aims to investigate transient dispersion and deposition of indoor particles under the heat recovery ventilation (HRV). Five groups of particles with different diameters ranging from 0.1 to 10 μm were taken into account, representing the inhalable indoor airborne particles. By considering three different heating systems, including the radiator, floor heating system and fan coil, the integrated ventilation-heating effects on particle dispersion were evaluated and compared. An Eulerian-Lagrangian CFD model was developed to predict turbulent characteristics of the airflow field and unsteady particle trajectories. The role of particle size, air change rate and outdoor temperature was addressed. In addition, influence of the heat source position on the particle decay rate and removal efficiency was investigated. The results indicated that the impact of heating system on the particle decay rate is weakened by increasing the ventilation rate. Among all heating systems, the radiator renders the highest dispersion rate and the slowest decay rate, even lower than a single HRV unit. It was revealed that, for an intermediate ventilation rate, the particle deposition rate in fan coil system is 3.6 and 2.4 times faster than the radiator and floor heating systems, respectively. It was also found that displacing the radiator to the opposite side of the ventilation unit quadruplicates the removal efficiency and leads to 146% enhancement of the decay rate coefficient.

Reductions in particulate matter concentrations resulting from air filtration: A randomized sham-controlled crossover study.

One-hundred seventy-two households were recruited from regions with high outdoor air pollution (Fresno and Riverside, CA) to participate in a randomized, sham-controlled, cross-over study to determine the effectiveness of high-efficiency air filtration to reduce indoor particle exposures. In 129households, stand-alone HEPA air cleaners were placed in a bedroom and in the main living area. In 43households, high-efficiency MERV 16 filters were installed in central forced-air heating and cooling systems and the participating households were asked to run the system on a clean-air cycle for 15min per hour. Participating households that completed the study received true air filtration for a year and sham air filtration for a year. Air pollution samples were collected at approximately 6-month intervals, with two measurements in each of the sham and true filtration periods. One week indoor and outdoor time-integrated samples were collected for measurement of PM2.5 , PM10 , and ultrafine particulate matter (UFP) measured as PM0.2 . Reflectance measurements were also made on the PM2.5 filters to estimate black carbon. True filtration significantly improved indoor air quality, with a 48% reduction in the geometric mean indoor PM0.2 and PM2.5 concentrations, and a 31% reduction in PM10 . Geometric mean concentrations of indoor/outdoor reflectance values, indicating fraction of particles of outdoor origin remaining indoors, decreased by 77%. Improvements in particle concentrations were greater with continuously operating stand-alone air cleaners than with intermittent central system filtration. Keeping windows closed and increased utilization of the filtration systems further improved indoor air quality.

Occupant behavior and indoor particulate concentrations in daycare centers

‘Occupant behavior’ is the primary mechanism determining indoor particulate concentrations. Various indoor human activities generate particulate matter. Human-building interactions, such as window opening behavior, change the number of outdoor particulate matter introduces to the building. ‘Daycare center’ where young children spend considerable time has an occupant schedule distinguished from other types of buildings. In the study, we analyzed the effects of occupant behavior on indoor particle concentrations in daycare centers by on-site monitoring. The measurements were performed in four daycare centers located in Gyeonggi-do, South Korea. Optical particle counters(OPS, model 3330, TSI Inc., Shoreview, MN, USA) were used for particulate concentration monitoring. The source strengths of particles resuspended by each human activity were calculated, and their contributions to indoor particle concentrations were evaluated. Further, characteristics of human-building interactions and their corresponding impacts on indoor air quality were also analyzed. Results showed that particle resuspension was greater when occupants were awake (mean, 41.0 particles·min−1) than when they were asleep (mean, 9.2 particles·min−1), and the contribution of occupant status was also higher when awake (37–70% vs. 8–18%) for particles sized (0.3–10.0 μm). Analyzing five detailed human activities, vacuuming (9.8·107 particles·min−1) emitted the highest amount of particulate matter per person, followed by physical activity (4.8·107 particles·min−1), sedentary activity (1.9·107 particles· min−1), meals (1.9·107 particles·min−1), and nap time (8.1·106 particles·min−1). The study suggests that vacuuming should be avoided while children are occupied. This research also shows that children could be exposed to high daily average indoor particulate concentration (up to 1217 particles·cm−3) when windows were opened for an extended period of time while poor outdoor air quality. These results indicate that indoor air quality can be severely degraded by opening windows without considering the level of outdoor particle concentration.

Effects of Evaporative Cooling Air Conditioning on Classroom Pollutants and Thermal Environment.

Indoor particles and carbon dioxide concentration are major indices to evaluate indoor air quality. Based on the two-dimensional filler sieving model of the direct evaporative cooling segment, the porous media model was used for the simulation of the water filler section, the filtering efficiency of particle was simulated by adjusting the water drenching density and airflow velocity in different operating conditions. The three-dimensional classroom model used to change the exhaust outlet position and control the use of air conditioners simulated the indoor thermal environment and the changes in pollutant concentration. The Euler method and Lagrangian method were used to analyze the indoor flow field and particle sieving in the direct evaporation section, respectively. Conclusions show that in the application of evaporative cooling and stratum ventilation air conditioning system in classroom, the position of the exhaust port affects the concentration of carbon dioxide in the student’s breathing area. The water filler section can effectively reduce the concentration of particle and carbon dioxide supplied indoors. The filtration efficiency of particle in outdoor air passing through the direct evaporative cooling section based on diffusion, inertial collision, and interception is affected by the combined effect of particle size, onward wind speed, and water spray density. The filtration efficiency of particle increases as the density of the spray water increases. With the increase of head-on wind speed, the filtration efficiency of coarse particulate matter is higher than that of fine particulate matter. The research results help policy makers decide whether to install evaporative cooling air conditioning in schools and determine which exhaust outlet positions are most effective in improving indoor air quality.

Ventilation strategies on indoor particles in day-care center

In this study, a day-care center located in Seoul was monitored for one year to quantify the effects of ventilation methods, natural and mechanical, on the indoor particle levels. It is found from the field monitoring that air tightness and mechanical ventilation system with MERV 12 can be helpful to maintain indoor particles at low levels during the class hours of the day-care center. The mechanical ventilation, however, is not sufficient for lowering PM2.5 when the outdoor PM2.5 is at high levels.

Indoor Air Pollution of Outdoor Origin: Mitigation Using Portable Air Cleaners in Singapore Office Building

Landscape fires in Indonesia and traffic pollution have been receiving increasing attention as sources of particulate matter (PM) in Singapore. Although mitigation measures to reduce PM levels using portable air cleaners (PACs) have been used in residential buildings, its application for office buildings is unknown. Using PAC, we demonstrated their potential for indoor particles removal in an office building and presented a method to evaluate their performance and estimate number of units to be deployed. Modelled and in-situ measured PAC effectiveness using up to twelve units was evaluated in three office sizes (30, 80 and 1490 m3). Measured effectiveness using indoor concentrations and indoor/outdoor ratios was obtained in a randomised intervention experimental design involving 3 weeks per location. Indoor particle concentration reductions in the three offices were dependent on particle size and confounded by variations in indoor emissions and outdoor levels resulting in low correlation and higher RMSE between modelled and measured effectiveness. PAC effectiveness computed using I/O ratios for removing UFP, PM2.5 and PM10 ranged 24–43%, 23–53% and 7–37% respectively. PAC has a higher in-situ effectiveness in small compared to larger spaces and the effectiveness is logarithmically dependent on the number of units deployed. We validated the use of our model to determine PAC effectiveness in the offices using up to eleven PACs (RMSE between modelled and measured data ranging from 3.9 to 6.6%). Lastly, we developed a design method to size the number of PAC needed for office buildings. The results from this study can be used for standards organization, policy makers and researchers interested in particle exposure reductions in large spaces.

Seasonal variation of size-fractionated particulate matter in residential houses in urban area in Vietnam: relationship of indoor and outdoor particulate matter and mass size distribution

The study aims to determine the concentration, size distribution and analyze the relationship of indoor and outdoor particles in urban area, in Vietnam. One thousand two hundred daily samples of PM0.1, PM0.1-0.5, PM0.5-1, PM1-2.5, PM2.5-10, PM>10 were taken simultaneously at four residential houses in summer and winter by nano sampler (Model 3182, Kinomax). The average concentrations of indoor PM0.1, PM0.5, PM1, PM2.5 and PM10 were in range of 5.3-8.9 μg/m3; 10.8-20.1μg/m3; 20.5-47.6 μg/m3; 33.7-105.9 μg/m3 and 44.7-135.0 μg/m3 among four houses, respectively. The concentrations of outdoor PM2.5, PM10 were considerately higher than those of indoor PM, whereas negligible differences on concentrations of PM0.1, PM0.5 and PM1 were observed. The significantly seasonal variation was observed for indoor PM1, PM2.5 and PM10, but not for PM0.1 and PM0.5. Majority of indoor fractions were origin from outdoor sources. Unimodal distributions of indoor particles determined the super-micron size (1 to 2.5 μm) with highest concentration and PM<0.5 and PM>10 with lowest concentration. Fine particles with interval sizes (PM0.5-1 and PM1-2.5) contributed to the predominance to coarse particles in both indoors and outdoors, suggesting serious threat on human health.

Analysis of Indoor Particle Diffusion in Attached Jet Air Supply System

With the change of the installation position of the radiant panel, the indoor air distribution formed by the attached jet air supply will also change, which will affect the diffusion distribution of indoor particulate matter. Through numerical simulation, the influence of indoor air distribution formed by attached jet air supply on the diffusion distribution of aerosol particles released by human body is studied. It is found that within 0 ~ 300s, 97.2% ~ 98.5% of the aerosol particles of human body jet are captured by the wall, and only a small part of fine particles exists in the air in the form of suspended solids. The final particle concentration of wall attached air supply is the lowest, and the effect of roof attached air supply is in the middle. The indoor particle concentration of wall attached air supply with deflector is higher than that of other forms at the same time in 0 ~ 300s.

Study on the change of indoor and outdoor air quality with height in high-rise buildings during the initial heating period

The indoor and outdoor pollutant concentrations of a high-rise building in Xi’an was tested and analyzed during the initial heating period in this paper. Also the relationship between indoor and outdoor pollutant concentration, building height and outdoor meteorological parameters in different periods was an-alyzed at the same time. Compare and analyze the ratio of indoor and outdoor particle concentration (I/O value) in different time periods. The results showed that during the test period, the concentration of partic-ulate matter reached the highest value at noon and the lowest value after dusk. The I/O value tends to de-crease with the increase of the building height, but at some moments there is a situation where the I/O value is greater than 1. The research results of this paper can provide a theoretical basis for indoor particulate control and architectural design of high-rise buildings.

Assessing residential indoor and outdoor bioaerosol characteristics using the ultraviolet light-induced fluorescence-based wideband integrated bioaerosol sensor.

We assessed and compared indoor and outdoor residential aerosol particles in a third-floor apartment from August through September 2020. The measurements were conducted using a direct-reading ultraviolet light-induced fluorescence (UV-LIF) wideband integrated bioaerosol spectrometer (WIBS). It measures individual particle light scattering and fluorescence from which particle properties can be derived. The number concentrations of total aerosol particles (TAP) and total fluorescent aerosol particles (TFAP) were significantly higher indoors. Daily and hourly TFAP mean concentrations followed the same trends as the TAP, both indoors and outdoors. The daily mean rank of the TFAP fraction (TFAP/TAP) was significantly higher indoors (23%) than outdoors (19%). Particles representing bacteria dominated indoors while particles representing fungi and pollen dominated outdoors. The mean volume-weighted median diameters for TFAP were 1.67 μm indoors and 2.09 μm outdoors. Higher TFAP fraction indoors was likely due to occupants' activities that generated or resuspended particles. This study contributes to understanding the characteristics of residential aerosol particles in situations when occupants spend most of their time indoors. Based on our findings, a large portion of all indoor aerosol particles could be biological (15-20%) and of respirable particle size (≥95%). Using a novel direct reading UV-LIF-based sensor can help quickly assess aerosol exposures relevant to human health.

Indoor Particulate Matters Measured in Residential Homes in the Southeastern United States: Effects of Pandemic Lockdown and Holiday Cooking

Although humans spend a majority of their lives in indoor environments, indoor air quality is immensely understudied, compared to ambient air. Here, we show the first long-term measurements of household indoor PM concentrations in the southeastern United States, for one year (May 2019 through April 2020) covering the COVID-19 hard-lockdown period (March and April 2020). Particle size distributions between 0.25–35 µm were measured with a low-cost sensor, which does not utilize hazardous chemicals and radiation sources and is ideal for indoor air monitoring in real households without disruption of residents’ living conditions. Our observations show that while cooking and cleaning are two major emissions sources for the residential indoor PM, consistent with the literature knowledge, but we also show that human occupancy affects the indoor PM level substantially. During the hard lockdown during the COVID-19 pandemic, the background level of indoor PM increased by ~200%, while the ambient PM decreased by ~50% during the same period. Before the pandemic, the indoor PM level was lower than the outdoor, but it became similar or higher than the outdoor level during the pandemic. Thanksgiving holiday cooking (prior to COVID-19) produced high concentrations of PM for an extended period (e.g., over 6 hours) even with active kitchen ventilation. PM concentrations during a cooking and cleaning event usually increased linearly to a maximum value and then decayed exponentially. The decay time of indoor PM ranged from several minutes up to ~100 minutes and increased with the particle size, indicating that particle deposition to the interior surfaces is the main sink process of the indoor PM.

Phase state of organic aerosols may limit temperature-driven thermodynamic repartitioning following outdoor-to-indoor transport

Ambient aerosols often experience temperature and humidity gradients following outdoor-to-indoor transport, causing organic aerosols (OA) to either gain or lose mass via gas-particle repartitioning. Recent models have sought to quantify these effects using equilibrium partitioning thermodynamics. However, evidence suggests some indoor OA may possess glassy or semisolid phase states with higher viscosities than liquid OA. Characteristic partitioning timescales of higher-viscosity particles are significantly longer than for liquid particles, which may either fully or partially inhibit repartitioning. For outdoor OA experiencing a temperature change during transport indoors, the ultimate repartitioning state depends on the relationship between the gas-particle partitioning rate coefficient (kgp) of semivolatile organics and the indoor particle loss rate coefficient (lp). That is, thermodynamic equilibrium partitioning may occur when semivolatile kgp ≫ lp, no repartitioning when semivolatile kgp ≪ lp, and partial repartitioning when their magnitudes are similar. Longer indoor particle lifetimes, higher particle number, and larger particle sizes all raise kgp (driving repartitioning towards equilibrium). For simulated U.S. residences, equilibrium condensation was likely reached in humid climate zones during warm meteorological conditions. In colder regions, the degree of evaporative repartitioning depended on whether organics could repartition before the particle phase state adjusts to indoor conditions, which is uncertain. When an appreciable temperature gradient exists, this study not only confirmed that all outdoor-originating OA that is liquid indoors will reach thermodynamic equilibrium, but also concluded that a plurality (46% for this domain) of such OA that is semisolid may also achieve thermodynamic equilibrium during its indoor lifetime.

Effect of Different Ventilation Systems on Concentrations of Indoor Particle Emitted from Floor of the Office

A three-dimensional numerical simulation of airflow, temperature, and pollutant concentration distributions with underfloor air distribution (UFAD) system and displacement ventilation (DV) systems are presented for different operating conditions. Since the particles deposited on the floors can be re-introduced into the air through re- suspension and then constitute a threat to human’s health, an optimal ventilation system is required to reduce the indoor air particle concentrations. In the present study, the effects of different systems on the concentrations of indoor particles are numerically investigated by an Eulerian-Lagrangian method, and the RNG k-ε model is adopted for the simulation. Three different supply air velocities (0.2-0.4 m/s) and different supply air temperatures (20 ℃, 22 ℃ and 24 ℃) are considered in the simulation. Meanwhile, the thermal effect of the human body on the micro-environment and its interaction with the surrounding environment are comprehensively evaluated. The simulation results shows that for the UFAD and DV systems, good performance of particle removal is obtained with the high air supply speed for the DV system, while under larger temperature gradient of the indoor environment, the UFAD system is capable of reducing the concentration of the particles emitted from the floors with lower air supply speed.

Spatio-Temporal Modeling of Small-Scale Ultrafine Particle Variability Using Generalized Additive Models

High-resolution measurements of ultrafine particle concentrations in ambient air are needed for the study of health human effects of long-term exposure. This work, carried out in the framework of the VIEPI project (Integrated Evaluation of Indoor Particulate Exposure), aims to extend current knowledge on small-scale spatio-temporal variability of Particle Number Concentration (PNC, considered a proxy of the ultrafine particles) at a local scale domain (1 km × 1 km). PNC measurements were made in the university district of San Lorenzo in Rome using portable condensation particle counters for 7 consecutive days at 21 sites in November 2017 and June 2018. Generalized Additive Models (GAMs) were performed in the area for winter, summer and the overall period. The log-transformed two-hour PNC averages constitute the response variable, and covariates were grouped by urban morphology, land use, traffic and meteorology. Winter PNC values were about twice the summer ones. PNC recorded in the university area were significantly lower than those observed in the external routes. GAMs showed a rather satisfactory result in order to capture the spatial variability, in accordance with those of other previous studies: variances were equal to 71.1, 79.7 and 84%, respectively, for winter, summer and the overall period.

Particulate Matter (PM) Adsorption and Leaf Characteristics of Ornamental Sweet Potato (Ipomoea batatas L.) Cultivars and Two Common Indoor Plants (Hedera helix L. and Epipremnum aureum Lindl. & Andre)

Particulate matter (PM) is a serious threat to human health, climate, and ecosystems. Furthermore, owing to the combined influence of indoor and outdoor particles, indoor PM can pose a greater threat than urban PM. Plants can help to reduce PM pollution by acting as biofilters. Plants with different leaf characteristics have varying capacities to capture PM. However, the PM mitigation effects of plants and their primary factors are unclear. In this study, we investigated the PM adsorption and leaf characteristics of five ornamental sweet potato (Ipomea batatas L.) cultivars and two common indoor plants (Hedera helix L. and Epipremnum aureum Lindl. & Andre) exposed to approximately 300 μg m−3 of fly ash particles to assess the factors influencing PM adsorption on leaves and to understand the effects of PM pollution on the leaf characteristics of plants. We analyzed the correlation between PM adsorption and photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), leaf area (LA), leaf width/length ratio (W/L), stomatal density (SD), and stomatal pore size (SP). A Pearson’s correlation analysis and a principal component analysis (PCA) were used to evaluate the effects of different leaf characteristics on PM adsorption. The analysis indicated that leaf gas exchange factors, such as Pn and Tr, and morphological factors, such as W/L and LA, were the primary parameters influencing PM adsorption in all cultivars and species tested. Pn, Tr, and W/L showed a positive correlation with PM accumulation, whereas LA was negatively correlated.

Negative Ion Purifier Effects on Indoor Particulate Dosage to Small Airways.

Indoor air quality is an important health factor as we spend more than 80% of our time indoors. The primary type of indoor pollutant is particulate matter, high levels of which increase respiratory disease risk. Therefore, air purifiers are a common choice for addressing indoor air pollution. Compared with traditional filtration purifiers, negative ion air purifiers (NIAPs) have gained popularity due to their energy efficiency and lack of noise. Although some studies have shown that negative ions may offset the cardiorespiratory benefits of air purifiers, the underlying mechanism is still unclear. In this study, we conducted a full-scale experiment using an in vitro airway model connected to a breathing simulator to mimic inhalation. The model was constructed using computed tomography scans of human airways and 3D-printing technology. We then quantified the effects of NIAPs on the administered dose of 0.5–2.5 μm particles in the small airway. Compared with the filtration purifier, the NIAP had a better dilution effect after a 1-h exposure and the cumulative administered dose to the small airway was reduced by 20%. In addition, increasing the negative ion concentration helped reduce the small airway exposure risk. NIAPs were found to be an energy-efficient air purification intervention that can effectively reduce the small airway particle exposure when a sufficient negative ion concentration is maintained.

Gas-particle partition and size-segregated distribution of flame retardants in indoor and outdoor air: Reevaluation on the role of fine particles in human exposure

In this study, we investigated the distribution of brominated and organophosphate flame retardants (BFRs and OPFRs) in the paired gaseous and nine size-segregated particulate samples collected from 8 typical indoor compartments and monthly outdoor in Xinxiang, China, respectively. For the indoor environments, total concentrations of FRs (Σ19FRs) in bulk air ranged from 3.9 ng/m3 to 37.5 ng/m3, with that in children recreation center (37.5 ng/m3) and furniture store (28.7 ng/m3) showing highest levels. In the outdoor air, Σ19FRs ranged from 3.1 ng/m3 to 13.6 ng/m3 among the 12 months, with that from late spring and summer being the highest. OPFRs had higher concentration than BFRs, with the total concentration of OPFRs accounting for 77%–99% of ∑19FRs. TCIPP (tris(chloroiso-propyl) phosphate), TCEP (tris(2-chloroethyl) phosphate), TEP (triethyl phosphate) and DBDPE (decabromodiphenyl ethane), BDE-209 (decabromodiphenyl ether) were the predominant analogs. Specifically, BFRs tended to enrich in gas phase indoors and coarse particles (aerodynamic diameters >3.3 μm) outdoors, but OPFRs mainly distributed in coarse particles both indoors and outdoors. The size distribution patterns varied among FRs, with the higher volatile FRs (e.g., TCEP, TCIPP) distributed more uniformly across particulate size. Although the distribution patterns of FRs in air were driven by multiple factors, organic carbon and element carbon in particulate matter had an influence to a certain extent. Health risks from exposure to FRs were characterized via the hazard quotient approaches. The total noncarcinogenic risks of ∑16FRs from inhalation were higher than that from air to skin transport, and the risks resulted from coarse particle-bound ∑16FRs (>3.3 μm) and gas phase were both significantly higher than that from fine fraction (<3.3 μm) in all scenarios, implying that FRs in coarse particles should not be underestimated.

An improved Markov chain model with modified turbulence diffusion for predicting indoor particle transport

Correctly predicting indoor particle transport is crucial for the design of air distribution to reduce the transmission of airborne infectious diseases. In recent years, a model for predicting particle transport based on the Markov chain technique has emerged, with the advantage of fast computing speed. However, the turbulence diffusion modeling approach in this Markov chain model is semi-empirical without justification. The present study aims to develop an improved Markov chain model with modified turbulence diffusion to increase its accuracy in predicting indoor particle transport. The proposed Markov chain model with modified turbulence diffusion was first validated with experimental data on transient particle transport under steady airflow from the literature. In addition, laboratory experiments on transient particle transport under unsteady periodic ventilation, which are rarely found in the literature, were conducted to further validate the improved Markov chain model. The results show that the improved Markov chain model can correctly predict transient particle transport under both steady and unsteady airflow in comparison with the experimental data. In addition, the improved Markov chain model was more accurate than the existing model in predicting transient particle transport, especially under unsteady airflow with periodic ventilation. By improving the turbulence diffusion modeling, the normalized root-mean-square deviation values of the Markov chain model decreased from 0.115/0.084 to 0.108/0.064 for the two cases in this study.