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A scale model experiment is an important method to study ventilation airflow pattern inside buildings that affects indoor air quality. The similitude criteria are the decision factors to guarantee using the result of model study to predict actual airflow of prototype. It is important to decide the similitude criteria between scale model and prototype. The aim of this project focuses on deciding the similitude criteria of a two-dimensional wall jet between the model and prototype to establish same airflow pattern in an isothermal mechanically ventilated enclosure. The parameters of the Reynolds number, Euler number, and jet momentum ratio proposed by previous researchers are investigated to find which parameter is the similitude criterion for a two-dimensional wall jet in isothermal condition. Experiments were conducted in two geometrically similar scale models. The similitude criteria were verified by comparing latent parameters with airspeed distribution following the kinematic similitude, whereas the airflow pattern following the dynamic similitude between the model and prototype. Experimental results indicate that the Euler number is not the similitude criterion, but the jet momentum ratio related to inlet airspeed is the similitude criterion of a two-dimensional wall jet in an isothermal mechanically ventilated enclosure. Reynolds number may be used as the similitude criterion only for flows at low Reynolds numbers. Our results are useful for the researcher to decide the parameters and boundary conditions of scale model study for the prediction of prototype performance of a two-dimensional wall jet in an isothermal mechanically ventilated enclosure.

The purpose of this article is to quantify the public health risk associated with inhalation of indoor airborne infection based on a probabilistic transmission dynamic modeling approach. We used the Wells-Riley mathematical model to estimate (1) the CO2 exposure concentrations in indoor environments where cases of inhalation airborne infection occurred based on reported epidemiological data and epidemic curves for influenza and severe acute respiratory syndrome (SARS), (2) the basic reproductive number, R0 (i.e., expected number of secondary cases on the introduction of a single infected individual in a completely susceptible population) and its variability in a shared indoor airspace, and (3) the risk for infection in various scenarios of exposure in a susceptible population for a range of R0. We also employ a standard susceptible-infectious-recovered (SIR) structure to relate Wells-Riley model derived R0 to a transmission parameter to implicate the relationships between indoor carbon dioxide concentration and contact rate. We estimate that a single case of SARS will infect 2.6 secondary cases on average in a population from nosocomial transmission, whereas less than 1 secondary infection was generated per case among school children. We also obtained an estimate of the basic reproductive number for influenza in a commercial airliner: the median value is 10.4. We suggest that improving the building air cleaning rate to lower the critical rebreathed fraction of indoor air can decrease transmission rate. Here, we show that virulence of the organism factors, infectious quantum generation rates (quanta/s by an infected person), and host factors determine the risk for inhalation of indoor airborne infection.

With the use of published temporal/seasonal size characteristics of fungal spores and meteorological data in the subtropical climate, we estimated the airborne fungal concentration indoor/outdoor (I/O) ratios in a wind-induced naturally ventilated home. We expanded previous size-dependent indoor air quality model based on a hygroscopic growth factor as a function of relative humidity (RH) on aerodynamic diameter and concentration of fungal spores. The average geometric mean diameters of airborne fungi decreased from outdoor 2.5870.37 to indoor 1.9170.12m mi n summer, whereas decreased from outdoor 2.7970.32 to indoor 1.7370.10mm in winter, resulting from the effect of hygroscopicity of airborne fungi. The higher indoor airborne fungal concentrations occurred in early and late afternoon in which median values were 699.29 and 626.20 CFU m � 3 in summer as well as 138.71 and 99.01 CFU m � 3 in winter, respectively, at 2 a.m. and 8 p.m. In the absence of indoor sources, summer has higher mean I/O ratios of airborne fungal concentration (0.29 – 0.58) than that in winter (0.12 – 0.16). Parsimoniously, our proposed RH-corrected I/O ratio model could be used to estimate the indoor source concentrations of bioaerosols provided that the actual measured fungus-specific I/O ratios are available. r 2004 Elsevier Ltd. All rights reserved.

This research proposes a multiple airflow regions gamma model to simulate airflow pattern in a ventilated airspace with mixing heterogeneity based on residence time distribution and gamma distribution statistics. We select p -cresol, toluene and p- xylene, three intensive odor causing volatile organic compounds (VOC-odor) found in swine housing, to account different mixing behaviors. By fitting the VOC-odor concentration profile calculated from VOC-odor transport model with three-parameter gamma distribution, we can characterize the extent of mixing and predict mixing heterogeneity in a ventilated livestock housing. A typical swine housing with a mechanical ventilation system in southern Taiwan was selected for model simulation. Results demonstrate that the mean residence time of p -cresol, toluene and p- xylene are 44.45±0.91, 267.30±58.90 and 332.38±129.83 h, whereas mean mixing factor are 0.20±0.05, 0.81±0.17, and 0.81±0.19, respectively, corresponding to a ventilation rate of 0.075±0.025 m 3 s −1 pig −1 within manure moisture content of 70±10%. This research gives additional physical information to characterize mixing behavior temporally and spatially with mean residence time and mixing factor, respectively, in a ventilated airspace with mixing heterogeneity. The robustness of multiple airflow regions gamma model can offer designers to reconsider the efficiency of ventilation systems through different mixing flow patterns in place of complete mixing hypothesis.

Scale-model study of a non-isothermal ceiling slot-ventilated enclosure was investigated in both airspeed and thermal fields. Results of airflow pattern, centerline velocity and centerline temperature decay, velocity and temperature profile, airflow boundary layer and thermal boundary layer growth, floor velocity, and floor temperature difference were analyzed to establish semi-empirical prediction equations. Results also compared with previous researches to validate the physical behavior of air-jet. Data of centerline velocity decay showed similar airflow characteristics as isothermal air-jet with Archimedes number ( Ar ) 0.004 , which performed as pseudo-isothermal airflow. Air-jet fell on entry with Ar > 0.018 . A single circulation airflow existed at 0.004 Ar 0.011 and two-circulation airflow occurred at 0.011 Ar 0.018 . The centerline velocity decay was fitted well as similar form of an isothermal condition. The centerline temperature decay was fitted well as the form of centerline velocity decay in both ceiling and floor regions. Both the velocity and temperature profiles agreed with results obtained from literature. Both airflow boundary layer and thermal boundary layer growths increased with traveling distance of air-jet. Maximum floor velocity and floor temperature difference were fitted well with different parameters. Analysis of airflow performance in a non-isothermal condition makes progress in predicting air quality inside the enclosures and guides the design concepts of ventilation system for an indoor environment.

A model describing odor causing volatile organic compounds (VOC-odor) transport in a ventilated airspace influenced by heterogeneity of adsorption surface of ambient aerosol and air mixing pattern is proposed and analyzed based on a transfer function modeling technique. In this study an advection-reaction impulse/step response function for VOC-odor is assumed. The system process presented by an ensemble transfer function is solved analytically in the Laplace domain. The analytical results are then numerically inverted using a modified fast Fourier transform algorithm. The model requires the specification of probability density function for residence time of airflow and for both equilibrium linear partitioning and first-order mass transfer rate parameters to quantify the specific air mixing pattern and transport processes. The model predicts the ensemble mean VOC-odor concentrations for a variety of adsorption kinetics and mixing pattern combinations as a function of the boundary impulse/step response inputs as well as residence time and adsorption rate statistics. The general behavior of output VOC-odor profiles is analyzed through the effects of mean adsorption rate coefficient, mean linear partitioning constant, mixing efficiency, mean residence time and coefficient of variations of both linear partitioning and rate coefficients. It indicates that when mixing/adsorption heterogeneity exists, simple complete mixing assumption and simple distribution of rate constant is inherently not sufficient to represent a more generally distributed mixing/adsorption process of VOC-odor transport in a ventilated airspace.

The ability of a simple linear response model is evaluated to explain the mixing efficiencies in an incomplete mixing ventilated airspace. Data interpretation and mean residence time calculation for a specified output concentration profile can also be evaluated. The residence time distribution (RTD) functions take the form of the two-parameter gamma distribution and account for different mixing types such as complete mixing, piston flow (no mixing), incomplete mixing, and various combinations of the above types. In these combinations, the different mixing types simulated by different RTDs conceptually represent airflow regions in series. The mixing efficiency was introduced to characterize the extent or degree of mixing in a ventilation system in that mixing efficiency equals zero for piston flow (no mixing), unity for complete mixing, and a value in between these two extremes for incomplete mixing. An environmental chamber experiment was conducted to generate several output profiles to evaluate the applicability of the model. Carbon dioxide was employed as the tracer gas. Our results show that an overall root-mean-squared error value of 8.64±5.25 ppm is low, indicating that the combination mixing patterns are generally found to be minimally biased and give better fitting than other simpler mixing patterns. Despite their neglect of molecular diffusion and possible temporal/spatial nonlinearities, these linear response models appear reasonably robust, making them at least as useful to building microenvironment designers in reconsidering the possibilities and consequences of various forms of incomplete mixing related to indoor air quality problems.

The ability of a transfer function modeling technique is evaluated to explain the odor causing VOCs (VOC-odor) transport processes influenced by heterogeneity of adsorption surface of ambient aerosol and air mixing pattern in a ventilated airspace. An advection–reaction impulse/step response function is used to generalize the dynamic transport of VOC-odor in heterogeneous mixing/adsorption ventilated airspace. The system process presented by an ensemble transfer function is solved analytically in the Laplace domain. The model requires the specification of probability density function (pdf) for residence time of airflow and for both equilibrium linear partitioning and first-order mass transfer rate parameters of gas/solid phase to quantify the specific air mixing pattern and transport processes. The model predicts the ensemble mean VOC-odor concentrations for a variety of adsorption kinetics and mixing pattern combinations as a function of the boundary impulse/step response inputs as well as residence time and adsorption rate statistics. The general behavior of output VOC-odor profiles is analyzed through the effects of mean adsorption rate coefficient, mean linear partitioning constant, mixing efficiency, mean residence time and coefficient of variations of both linear partitioning and rate coefficients. This study indicates that when mixing/adsorption heterogeneity exists, simple complete mixing assumption and simple distribution of rate constant are inherently not sufficient to represent a more generally distributed mixing/adsorption process of VOC-odor transport in a ventilated airspace.

A model called the multiple airflow regions gamma model (MARGM) was developed based on a continuous distribution of residence time for predicting the mixing behavior in a ventilated airspace in that data interpretation and mean residence time calculation for a specified output concentration profile can also be evaluated. The MARGM takes the form of the two-parameter gamma distribution and accounts for different mixing types: complete mixing, no mixing (piston flow), incomplete mixing, and various combinations of the above types. In these combinations, the different mixing types simulated by the MARGM conceptually represent airflow regions in series. The mixing efficiency was introduced to characterize the extent or degree of mixing in a ventilation system. Mixing efficiency equals zero for piston flow (no mixing), unity for complete mixing, and a value in between these two extremes for incomplete mixing. The MARGM simulates the combinations of complete mixing, incomplete mixing, and piston flow. Therefore, seven models are introduced in this effort: complete mixing model, piston flow model, complete-piston flow model, complete-incomplete-piston flow model (the general model), complete-incomplete mixing model, incomplete-piston flow model, and incomplete mixing model. The applicability of models was tested by several case studies. Results show that combination models give better fitting than other simpler models. The MARGM enables building microenvironment designers reconsider the possibilities and consequences of various forms of incomplete mixing in investigating indoor air quality problems.

A mathematical model was derived to calculate swine manure cleanup criteria for odor causing volatile organic compounds (VOCs) so that acceptable total dose would not exceeded through the inhalation of ventilation air in swine housing for workers and pigs. A hypothetical scenario was used which assumed that subsurface contaminant in swine manure diffuses through a layer of manure-air interface then is swept into the ventilated airspace via advection, where long-term inhalation of contaminant was assumed to occur. The philosophy of the transport model is to incorporate the age distribution of contaminated air and a first-order decay of contaminant sources into the diffusion model for simulation of air concentrations of VOCs and total exposure dose. A closed-form solution is presented to allow a series of numerical experiments for investigating the effects of adsorption characteristics between manure gas and manure, the mean age of contaminated air, effective diffusivity, and degradation coefficient on total dose. Swine manure cleanup criteria based on non-exceedence of the total hazardous dose corresponding to an acceptable risk from indoor inhalation of four selected VOCs of p-cresol, hexane, toluene, and xylene were calculated in a typical pig unit. The model can be used in the future to compute the relative effectiveness of VOCs filtration systems and/or altered ventilation rates on the VOC exposure problem in animal housing.

This paper describes a novel idea of linking models of exposure, internal dosimetry, and health effects. Risk assessment approach that integrates predicted odor caused by volatile organic compounds (VOC-odor) of toluene/xylene concentrations in human tissues leads to predict exposure risks in livestock buildings. First, VOC transport model was developed to calculate airborne toluene/xylene concentrations. Based on a physiologically based pharmacokinetic (PBPK) model, concentrations within five compartments representing lung, liver, fat, slowly perfused tissues, and rapidly perfused tissues could be quantified. By using a pharmacodynamic (PD) Hill model, we can optimally fit data from rat and human experiments to reconstruct dose–response relationships for accounting human health effects from nose poke and eye irritation. Results demonstrated that peak tissue concentration occurring at 5–10 h in that fat contains the highest concentration than other tissues at around 4 ppm of toluene and 1.8 ppm of xylene. The EC10 values are 114 and 232 ppm, whereas expected risks are estimated to be 0.71% and 0.26% of human exposure to toluene and xylene, respectively. Risk analyses indicate that inhalation exposure in livestock buildings poses no significant threat to human health under the present environmental conditions. This method provides a rigorous and effective approach to relate target tissue concentration to human nose poke or eye irritation. We suggest that our probabilistic framework and methods be taken seriously because they produce general conclusions that are more robust and could offer a risk-management framework for discussion of future establishment of limits for respiratory exposure to VOC-odor.

We appraised organ-specific toxicokinetics and dose responses of arsenic burdens in tilapia Oreochromis mossambicus. We kinetically linked an Area-under-the-curve (AUC)-based acute toxicity model and a pharmacodynamic model to derive dose-response relationships between equilibrium organ-specific arsenic concentrations and mortality effects. The AUC-based acute toxicity model was also used to derive organ-specific internal effect concentration (IEC)-time-response relationships, which can also be applied to predict a time-mortality profile. We conducted a 7-day exposure experiment to obtain toxicokinetic parameters, whereas the AUC-based acute toxicity model was verified with LC50(t) data obtained from a 7-day acute toxicity bioassay. Our results demonstrated that 96-hour LC50 and incipient LC50 for tilapia exposed to arsenic are 28.68 (95% confidence interval to 24.92 to 32.44) and 25.55 mg L(-1), respectively. Dose-response relationships followed the Hill equation, which could be expressed as organ-specific bioconcentration factors and incipient LC50. Organ-specific dose-response relationships showed that muscle, gill, and liver have a relatively steep sigmoid dose-response profile in that IEC50 were 26.6, 62.5, and 78.5 microg g(-1) dry wt (dw), respectively. Organ-specific arsenic internal lethal burdens were the highest in the gill and the lowest in the muscle in waterborne-exposed tilapia. The IEC and target-organ concentrations derived in this study can be used in site-specific risk assessment.

We investigated the effect of indoor sources including Chinese-style cooking, incense burning, cleaning, and people's moving on indoor particle size distributions and concentrations and calculated the personal exposure dose rates in the human respiratory tract (HRT) using time-activity and indoor and outdoor particle size distribution data collected from a traditional Taiwanese residence in central Taiwan region. We applied a simple size-dependent indoor air quality model associated with a compartmental lung model to determine the source emission rates and exposure dose. Cooking and incense burning had size-integrated source emission rates of 0.042+/-0.024 (mean+/-S.D.) and 0.038+/-0.026 particles s(-1), respectively. Cooking and incense burning were significant contributors to indoor particle levels for particle sizes from 0.5 to 5 microm in that the percent contributions to indoor concentrations were 0.334+/-0.02 and 0.267+/-0.035, respectively. Our results demonstrated that extrathoracic (ET) region had higher average PM mass lung/indoor ratio (0.77) than that of bronchial (BB) (0.52), bronchiolar (bb) (0.27) and alveolar-interstitial (AI) (0.14) regions from both cooking and incense burning events. The average integrated deposition dose rates (particles cm(-2) h(-1)) of 24.11 in ET, 4.68 in BB, and 7.89 in bb were higher than that of 0.011 in AI for both cooking and incense burning events. This research illustrates that exposure assessment based on time-activity and real-time behavior of particle data can provide valuable information on the fate of indoor particles and hazard to human health.

A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models were developed for arsenic (As) in tilapia Oreochromis mossambicus from blackfoot disease area in Taiwan. The PBPK/PD model structure consisted of muscle, gill, gut wall, alimentary canal, and liver, which were interconnected by blood circulation. We integrate the target organ concentrations and dynamic response describing uptake, metabolism, and disposition of As and the associated area-under-curve (AUC)-based toxicological dynamics following an acute exposure. The model validations were compared against the field observations from real tilapia farms and previously published uptake/depuration experimental data, indicating that predicted and measured As concentrations in major organs of tilapia were in good agreement. The model was utilized to reasonably simulate and construct a dose-dependent dynamic response between mortality effect and equilibrium target organ concentrations. Model simulations suggest that tilapia gills may serve as a surrogate sensitive biomarker of short-term exposure to As. This integrated As PBPK/PD/AUC model quantitatively estimates target organ concentration and dynamic response in tilapia and is a strong framework for future waterborne metal model development and for refining a biologically-based risk assessment for exposure of aquatic species to waterborne metals under a variety of scenarios.

Two models for evaluating the contents and advection of manure moisture on odor causing volatile organic compounds (VOC-odor) volatilization from stored swine manure were studied for their ability to predict the volatilization rate (indoor air concentration) and cumulative exposure dose: a MJ-I model and a MJ-II model. Both models simulating depletion of source contaminant via volatilization and degradation based on an analytical model adapted from the behavior assessment model of Jury et al. In the MJ-I model, manure moisture movement was negligible, whereas in the MJ-II model, time-dependent indoor air concentrations was a function of constant manure moisture contents and steady-state moisture advection. Predicted indoor air concentrations and inhaled doses for the study VOC-odors of p-cresol, toluene, and p-xylene varied by up to two to three orders of magnitude depending on the manure moisture conditions. The sensitivity analysis of both models suggests that when manure moisture movement exists, simply MJ-I model is inherently not sufficient to represent a more generally volatilization process, which can even become stringent as moisture content increases. The conclusion illustrates how one needs to include a wide variety of manure moisture values in order to fully assess the complex volatilization mechanisms that are present in a real situation.

A mathematical model taking into account source depletion with time and the actual thickness of manure layer was derived to evaluate indoor inhalation exposure dynamics to three selected odor causing volatile organic compounds (VOC-odors) of p-cresol, toluene, and xylene volatilization from stored pig slurry. The model assumes that pig slurry is undisturbed and the VOC-odors released in a contaminated layer and transported through a clean layer as well as a manure-air interface boundary. The model simulates time-dependent volatilization, the depletion of source contaminant via both volatilization and degradation, and could be used with a contaminated zone of finite thickness. For a given VOC-odor, the predicted total exposure and resulting manure cleanup criteria can be a large variability depending on the model whether a finite or infinite manure layer thickness was considered. Results obtained from model comparisons suggest that the model incorporating depth-varying of manure layer and contaminant source depletion is more suitable to evaluate the VOC-odor exposure dynamics in swine housing bioclimate.