Particles mitigation and decontamination by impinging jets is commonly used in various engineering in both indoor and outdoor settings. The current research is concerned with advancing the understanding of the phenomena occurring under the specific linear cylindrical nozzle, as well as under the oblique linear nozzle in general. The numerical method is extensively validated using published experimental data before being applied to the configuration of interest. The results demonstrate large differences between the forward and leeward maximal shear stress and rate at the surface impacted by the oblique jet and the impact of the macro-roughness on their values.

Re-suspension of particulate matter under human activity can have a significant impact on particle concentrations in indoor environments. The removal of surface-bound particulates as a person's foot contacts a substrate and the subsequent transport of such particulates through wake entrainment effects and through deposition is an important mechanism for particle dispersion. To study aspects of this event, we perform high-fidelity simulations of particle transport due to the heel-to-toe contact of a foot with a particle-laden carpet. For this purpose, an immersed boundary method is extended to account for particle transport, re-suspension, and deposition near the surface of the foot. Particle deposition is modeled as a combination of gravitational settling, Brownian diffusion, and convective impaction, while a dynamic re-suspension model is used to model particle re-suspension from the surfaces. We demonstrate the details of transient transport phenomena of re-suspended particles during a heel-to-toe foot motion event. The effects of the thickness of the carpet layer, the foot penetration depth into the carpet layer, the foot speed, and particle sizes on the mass re-suspended are investigated. Parametric studies show that a deeper foot penetration into a thinner carpet layer increases particle re-suspension and a faster foot motion also increases the re-suspension. Re-suspension rates increase as the particle size increases for particles in a size range of 1-20 mu m. Predicted re-suspension rates are compared with those obtained in recent experiments.

This work provides an understanding of how airflow patterns around humans can affect the concentrations and particle size distributions of particulate matter (PM) in the breathing zone. The focus of the experiments reported here is the flow around a child-size manikin under various conditions, including changes in body heat, breathing, wind speed, and body orientation relative to the wind direction. The airflow patterns that develop were investigated using laser Doppler anemometry. The presence of body heat changes the flow pattern most dramatically. With the manikin at room temperature, the flow pattern on the downstream side of the manikin consists of two slowly recirculating eddies. With the addition of body heat to the manikin, the flow pattern downstream of the manikin changes to a rising vertical plume with velocities on the order of 0.1 m/s. This vertical plume is capable of transporting PM into the breathing zone from near the floor. Increased wind speed decreases the relative importance of buoyancy. As the wind speed increases from 0.1 to 0.3 m/s, the vertical plume on the downstream side of the manikin is replaced by two recirculating eddies, a flow pattern similar to that with the unheated manikin. Changes in the relative importance of body heat and free-stream wind speed are quantified using a type of Richardson number.

The Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) field study examined indoor and outdoor exposure to traffic-generated air pollution by studying the individual processes of generation of traffic emissions, transport and dispersion of air contaminants along a roadway, and infiltration of the contaminants into a residence. Real-time instrumentation was used to obtain highly resolved time-series concentration profiles for a number of air pollutants. The B-TRAPPED field study was conducted in the residential Sunset Park neighborhood of Brooklyn, NY, USA, in May 2005. The neighborhood contained the Gowanus Expressway (Interstate 278), a major arterial road (4(th) Avenue), and residential side streets running perpendicular to the Gowanus Expressway and 4(th) Avenue. Synchronized measurements were obtained inside a test house, just outside the test house façade, and along the urban residential street canyon on which the house was located. A trailer containing Federal Reference Method (FRM) and real-time monitors was located next to the Gowanus Expressway to assess the source. Ultrafine particulate matter (PM), PM(2.5), nitrogen oxides (NO(x)), sulfur dioxide (SO(2)), carbon monoxide (CO), carbon dioxide (CO(2)), temperature, relative humidity, and wind speed and direction were monitored. Different sampling schemes were devised to focus on dispersion along the street canyon or infiltration into the test house. Results were obtained for ultrafine PM, PM(2.5), criteria gases, and wind conditions from sampling schemes focused on street canyon dispersion and infiltration. For comparison, the ultrafine PM and PM(2.5) results were compared with an existing data set from the Los Angeles area, and the criteria gas data were compared with measurements from a Vancouver epidemiologic study. Measured ultrafine PM and PM(2.5) concentration levels along the residential urban street canyon and at the test house façade in Sunset Park were demonstrated to be comparable to traffic levels at an arterial road and slightly higher than those in a residential area of Los Angeles. Indoor ultrafine PM levels were roughly 3-10 times lower than outdoor levels, depending on the monitor location. CO, NO(2), and SO(2) levels were shown to be similar to values that produced increased risk of chronic obstructive pulmonary disease hospitalizations in the Vancouver studies.

This research effort was aimed at understanding how foot motion affects air transport and thus how walking affects contaminant dispersion. Particle imaging velocimetry (PIV) showed that during a rotational motion of the foot (typical footstep), a draft corner flow develops that carries particles from heel to toe. Foot contact with the floor may result in one or both of two types of reentrainment: (1) particles become airborne due to detachment from the floor, and (2) particles are first collected by the foot cover (e.g., Tyvek) and then detached from the foot into the airflow produced by the foot rotation. The airflow under the rotating foot was modeled as a rotating corner flow, and it was shown that such modeling can capture major characteristics of the airflow generated by the rotating foot and can explain how rotational foot motion contributes to reentrainment and dispersion of contaminants.

This paper presents data analysis from the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study to assess the transport of ultrafine particulate matter (PM) across urban intersections. Experiments were performed in a street canyon perpendicular to a highway in Brooklyn, NY, USA. Real-time ultrafine PM samplers were positioned on either side of an intersection at multiple locations along a street to collect time-series number concentration data. Meteorology equipment was positioned within the street canyon and at an upstream background site to measure wind speed and direction. Time-series analysis was performed on the PM data to compute a transport velocity along the direction of the street for the cases where background winds were parallel and perpendicular to the street. The data were analyzed for sampler pairs located (1) on opposite sides of the intersection and (2) on the same block. The time-series analysis demonstrated along-street transport, including across the intersection when background winds were parallel to the street canyon and there was minimal transport and no communication across the intersection when background winds were perpendicular to the street canyon. Low but significant values of the cross-correlation function (CCF) underscore the turbulent nature of plume transport along the street canyon. The low correlations suggest that flow switching around corners or traffic-induced turbulence at the intersection may have aided dilution of the PM plume from the highway. This observation supports similar findings in the literature. Furthermore, the time-series analysis methodology applied in this study is introduced as a technique for studying spatiotemporal variation in the urban microscale environment.

High-density housing in close proximity to freeways in conjunction with high concentrations of traffic emissions may contribute to significant degradation of indoor air quality. Densely populated areas may also be targeted for intentional releases of biological or chemical agents because an urban release could result in higher morbidity and mortality from the attack. Since people tend to spend the majority of their time indoors, it is paramount to explore the relationships between outdoor and indoor air quality and, specifically, the time scales that characterize transport of airborne contaminants from outdoors to indoors. In the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study, a three-story row house with a flat face and roof and multiple rooms was used to investigate outdoor-to-indoor contaminant time scales. The building was located in the Sunset Park neighborhood of Brooklyn, NY, USA, in the vicinity of a major expressway and a heavily trafficked arterial road. It was found that the building shell has a profound impact on the indoor concentrations. A strong hourly periodicity (see Eisner et al., this issue, DOI: 10.1039/b907132f) in concentration outside the building during the morning "rush hour" was used as evidence to suggest that indoor contaminants originated from outdoor air penetration. Although the indoor concentrations followed a similar pattern, indoor concentrations were found to be more persistent than outdoor concentrations. Stronger persistency is used here to describe the tendency of the indoor concentration to continue to rise even if the outdoor concentration has started to drop, or vice versa. This may be an important factor in assessing negative health risks to inhabitants or first responders. A cross-correlation technique was employed to study the correlation between outdoor and indoor time series. In the high-density housing residential building used in the study, it was found that a long lag time exists (11 min) before indoor and outdoor concentrations reach maximal correlation.

The Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study, conducted in Brooklyn, NY, USA, in 2005, was designed with multiple goals in mind, two of which were contaminant source characterization and street canyon transport and dispersion monitoring. In the portion of the study described here, synchronized wind velocity and azimuth as well as particulate matter (PM) concentrations at multiple locations along 33rd Street were used to determine the feasibility of using traffic emissions in a complex urban topography as a sole tracer for studying urban contaminant transport. We demonstrate in this paper that it is possible to link downwind concentrations of contaminants in an urban street canyon to the vehicular traffic cycle using Eigen-frequency analysis. In addition, multivariable circular histograms are used to establish directional frequency maxima for wind velocity and contaminant concentration.

Computational fluid dynamics (CFD) and numerical investigations of particle inhalability and contaminant exposure have used simple geometrical surrogates for a breathing human form, but the effect of eliminating facial features has not been investigated. In this work, the velocity field and particle aspiration associated with two differently shaped mannequins were investigated to determine if an elliptical form was sufficient to represent the complexity of fluid flow associated with an inhaling human. Laser Doppler anemometry was used to measure velocity, and both optical sizing and gravimetric analysis were used to measure particle aspiration from an aerosol source. All tests were performed with continuous inhalation through the mouth, with the mannequin facing the 0.3 m s(-1) freestream. Although limitations in the laser Doppler optics prevented velocity measurements at distances <11 mm in front of the mannequin mouth opening, significant velocity differences were identified up to 20 mm in front of the mouth opening. This indicated that facial features affected the flow field near the face only. Owing to these differences, particle aspiration was compared between mannequins for three different velocity ratio conditions using an aerosol source. Even with relatively large variability in the aspirated concentration in this study, the aspirated mass concentration was significantly less for the anatomical mannequin relative to the elliptical form. Thus, the simplified elliptical cylinder does not sufficiently characterize the fluid dynamics near the mouth of an inhaling human form at these limited test conditions. Future CFD and numerical simulations to investigate human aspiration of particles should incorporate the complex features of the human face to investigate adequately particle aspiration in low velocity environments.

This paper presents verification and validation results for the time-averaged, three-dimensional velocity field immediately downstream of a finite elliptic cylinder at a Reynolds number of 1.35×104. Numerical simulations were performed with the finite element package, Fidap, using the steady state, standard k-epsilon model. The ratio of the cylinder height to the major axis of the elliptical cross section is 5.0; the aspect ratio of the cross section is 0.5625. This particular geometry is selected as a crude surrogate for the human form in consideration of further applied occupational and environmental health studies. Predictions of the velocity and turbulence kinetic energy fields in the very near-wake are compared to measurements taken in a wind tunnel using laser Doppler anemometry. Results show that at all locations where a reliable grid convergence index can be calculated there is not a demonstrable difference between simulated and measured values. The overall topology of the time-averaged flow field is reasonably well predicted, although the simulated near-wake is narrower than the measured one.

A novel aerosol generation system has been constructed for use in a large wind tunnel for two distinct research projects. One project requires a uniform aerosol concentration over the wind tunnel cross section, while the other project demands a stratified aerosol concentration distribution. The system consists of an array of venturi nozzles, which entrains particulate matter from a moving conveyor belt and disperses it into the tunnel under the force provided by a compressed air source. For the stratified release configuration, only the bottom row of nozzles was used and a confinement sleeve was installed to prevent mixing with clean air; the mixing fans were omitted from this configuration. The uniform release arrangement was tested by gravimetrically measuring particle concentration over the cross section of the tunnel for tunnel speeds of 0.1 and 1.0 m/s; uniformity was achieved within a coefficient of variation of 6.4%. The stratified distribution results show a high concentration near the floor, which diminishes with increased height. Particle size distribution was also determined on filter samples using scanning electron microscopy analysis for the uniform release experiments. No appreciable difference in mass median diameter or geometric standard deviation could be discerned for the various sampling points.

In July, 1997, the EPA promulgated a new National Ambient Air Quality Standard (NAAQS) for fine particulate matter (PM2.5). This new standard was based on the collection of an integrated mass sample on a filter. Field studies have demonstrated that the collection of semivolatile compounds leads to artifacts and imprecision among methods. In view of such sampling artifacts, a test requirement was promulgated in Title 40, Part 53, Subpart F, Section 53.66 of the Code of Federal Regulations (40CFR53.66) to aid in the determination of methodological equivalency. In this paper, this requirement is critically reviewed and tested in terms of its feasibility and precision. The results show that the test is capable of demonstrating acceptable precision for FRM-type samplers and repeatable differences in performance among different methods. In order to maintain high precision within the entire test procedure, the loading time should be extended to 2 h for flow rates of 16.7 lpm and proportionately longer for lower flow rates.

Research into the wind microclimate and its effect on the accuracy and effectiveness of passive aerosol monitors is expanding as the importance of personal monitoring versus regional monitoring increases. The important phenomena for investigation include thermal and dynamic effects of the human body, contaminant dispersion around a human body and within a building complex, and the wind environment within a building (indoor/outdoor) complex. This paper demonstrates that the microclimate around the human body plays a critical role in contaminant transport near the body and thus can affect particle concentration measurements by personal samplers.

A universal bifurcation model developed to study a variety of transport phenomena in the human lung is described. This paper focuses on technical specifications of the model and on local particle concentration patterns within post-bend and post-bifurcation zones. Results are presented for uniformly sized solid microspheres, 1.4 μm in diameter, over a range of steady air velocity conditions. It is shown that local particle concentration can be significantly higher than the initial concentration, which demonstrates that the particle phase component of the aerosol is not incompressible (de la Mora, 1985, Aerosol Sci. Technol.4, 339–349; Konstandopoulos, 1990, J. Aerosol Sci.21, 983–987), and that a significant boundary layer particle concentration enhancement in the post-bend,/bifurcation zone can be produced by the vortices originated in bends and bifurcations.

Using transient size and temperature measurements obtained on a small thermocouple (TC) bead suddenly immersed in the soot-laden combustion products downstream of a water-cooled premixed flat-flame burner, we demonstrate that soot deposition rates are dominated by particle thermophoresis, i.e., soot particle drift down the temperature gradient prevailing in the gas thermal boundary layer (BL) surrounding the TC target. Observed soot deposition mass fluxes are estimated to be up to three orders of magnitude greater than those that would be expected on the basis of only Brownian (concentration) diffusion at the prevailing Reynolds numbers. It is shown that, for thermophoretically dominated soot particle transport, a suitable plot constructed from the transient TC-bead output should yield a straight line whose slope is proportional to the local soot volume fraction in the combustion gases. The latter dependence has been tested at several flame stoichiometries and heights above the burner surface, using the independent experimental technique of line-of-sight laser light (0.63 μm) extinction. Our results suggest that under these conditions small thermocouples can be used not only to estimate local gas temperatures, but also local soot volume fractions, without requiring restrictive assumptions about the prevailing particle size distribution, particle optical properties, or flame gas uniformity/symmetry. We conclude that (a) the dependence of the soot deposition rate on temperature “contrast” is in excellent accord with recently proposed thermophoretic BL-theories, and (b) the behavior of submicron soot particles in nonisothermal combustion products is strongly influenced by thermophoresis, with important implications for understanding rates of soot nucleation, growth, coagulation, burnout, and deposition.

The rotational diffusion coefficient and the gradient rotational velocities of Brownian cylindrical and discoidal aerosol particles in a pure shear flow were calculated for free molecular regime conditions. The calculations were carried out via the evaluation of the torque operating on the rotating particles due to the momentum exchange with the gas molecules. To that purpose, Chapman's truncated velocity distribution function was adopted and Maxwell's boundary conditions for the reflected molecules used. Under justifiable approximations, it was obtained that the torque along particles' axis i can be given by an equation of the type TM,i = −Aωi + Fi, where Ai is exactly the inverse of the mobility of the particle in a still medium, ωi is its rotational velocity component, and Fi is a function of the particles' orientation and flow gradient. By employing this expression in the Euler equations of rotation and solving the latter numerically as well as analytically for a specific case, it was found that after a negligible transient time the particles acquire an asymptotic gradient rotational velocity identical with the value achieved by neglecting their acceleration. This asymptotic (gradient) rotational velocity was observed to be essentially identical with the classical fluid dynamic values of Jeffery for prolate ellipsoids of the same axes as our particles and which are immersed in a similar flow. An explanation of this equality is offered.

The rotational diffusion diadic of nonspherical aerosol particles in the free-molecular regime was calculated by a statistical mechanical method. The method was tested on a sphere whereby an expression identical to that of Epstein was obtained. It was applied with no loss of generality to a finite cylinder which represents an important class of particles such as very small fibers. The values of the diffusion coefficient for Brownian rotation about the middiameter of the cylinder were computed for typical aerosol cases and compared to those calculated by Edwards on continuum theory basis. In the range of particle dimensions checked, the former were higher than the latter by about two orders of magnitude. To illustrate the place of Brownian rotation in the transport of nonspherical particles, a typical deposition situation of cylindrical fibers on a planar surface was examined.