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Simulation results of microparticle and nanoparticle deposition patterns, local concentrations, and segmental averages are contrasted for a human upper airway model starting from the mouth to planar airway generation G3 under different inspiratory flow conditions. Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler–Euler (nanoparticles) or the Euler–Lagrange (microparticles) approach was employed with a low-Reynolds-number k – ω model for laminar-to-turbulent airflow and submodels for particle-phase randomization. The results show that depositions of both micro- and nano-size particles vary measurably in the human upper airways; however, the deposition distributions are much more uniform for nanoparticles. The maximum deposition enhancement factor, which is defined as the ratio of local to average deposition concentrations, ranges from about 40 to 2400 for microparticles and about 2 to 11 for nanoparticles with inspiratory flow rates in the range of 15 ⩽ Q in ⩽ 60 l/min. In addition, some airway bifurcations in generations G0 to G3 subjected to high inlet flow rates (say, Q in = 60 l / min ) may receive only very small amounts of large micro-size particles (say, with aerodynamic diameter d ae ⩾ 10 μ m ) due to largely preferred upstream deposition. It has been hypothesized that, uniformly deposited nanoparticles of similar concentrations may have greater toxicity effects when compared to microparticles of the same material.

Particle deposition in human lungs was investigated theoretically considering a stochastic variation of airway morphology using a Monte Carlo method. In computing the total and regional deposition each airway generation was divided into infinitesimal volume segments and each volume segment was allowed to pass through randomly selected airway branches of which morphology (e.g., airway dimensions and branching angle) was varied randomly. Deposition values obtained by the Monte Carlo method were compared with those obtained by the traditional deterministic method. It was found that the Monte Carlo method predicted deposition values generally comparable to those predicted by deterministic method for sub-micron size particles. However, for micron size particles the Monte Carlo method provided greater deposition values in the proximal airway regions where deposition occurs mainly by inertial impaction. The difference could be attributed to the non-linear relationship between deposition efficiency and airway dimensions in the inertial deposition regime. The results suggest that a Monte Carlo method may be a useful tool for evaluating deposition of inhaled particles in the lungs with a wide variation of airway dimensions.

Laminar-to-turbulent air flow for typical inhalation modes as well as micro-particle transport and wall deposition in a representative human oral airway model have been simulated using a commercial finite-volume code with user-enhanced programs. The computer model has been validated with experimental airflow and particle deposition data sets. For the first time, accurate local and segmentally averaged particle deposition fractions have been computed under transitional and turbulent flow conditions. Specifically, turbulence that occurs after the constriction in the oral airways for moderate and high-level breathing can enhance particle deposition in the trachea near the larynx, but it is more likely to affect the deposition of smaller particles, say, St

A polydisperse aerosol inhalation system has been developed to measure particle deposition in the lungs of human subjects. Nebulizers are used to generate aerosols with mass median aerodynamic diameters from 0.3 to 3 μm , and geometric standard deviations of 1.8–2.0. Inspired aerosol is drawn from a holding bag, passes through a sliding valve and a pneumotachograph, and enters a heated mouthpiece. Exhaled aerosol passes from the mouthpiece and pneumotachograph, through a second sliding valve and is collected in a heated sample bag. Inhalation and exhalation valves trigger automatically with change in flow direction through the pneumotachograph. Complete size distributions of inhaled and exhaled aerosol are measured by an aerodynamic particle sizer and a scanning mobility particle sizer. Fractional particle deposition of a test aerosol in the lung is determined by comparing inhaled and exhaled aerosol size fractions. Total deposition is determined from the sum of the fractional depositions. This new system precludes the need for monodisperse aerosol series to simulate polydisperse aerosol data, thus substantially reducing both study length and subject exposure.

Laminar oscillatory inhalation flow as well as micron-particle transport and wall deposition in a representative triple bifurcation airway model have been simulated using a commercial finite-volume code with user-enhanced programs. The computer model has been validated with experimental particle deposition data and deposition patterns for double bifurcations. The transient air flow, particle transport, and wall deposition patterns were analyzed and summarized in terms of particle deposition efficiencies (DEs) and surface density maps. Particle deposition may increase under cyclic flow conditions, i.e., DE-values are typically larger for cyclic flow than for steady flow at the mean flow rate of a given inhalation pulse. The maximal relative difference between these two DE-values may be as high as 50% for 0.02⩽Stmean⩽0.12 during normal inspiration (Q in =30 l / min ) . However, matching inlet Reynolds and Stokes numbers are proposed, which generate under quasi-steady flow conditions very similar DE-values and deposition patterns as in equivalent pulsatile flow. The relative differences between DE-values for cyclic and matching steady cases are less than 5%. The quantitative results of this work are of interest to researchers either conducting health risk assessment studies for inhaled particulate pollutants or analyzing drug aerosol deposition at desired lung target sites.

This paper presents the development and evaluation of ambient fine particle concentrators for conducting animal and human exposure studies. These systems utilize the technology of virtual impactors to concentrate particles in the range 0.15--2.5 μm. Ambient particles are first drawn at 5000 1m -1 through a preselective inlet that removes particles above 2.5 μm. Subsequently, the remaining aerosol is drawn through a series of virtual impactors, which increase particle concentration by a factor of about 10 and 30, for human and animal exposures, respectively. Results from the experimental characterization of the concentrators showed that the concentration enrichment process occurs without any distortion in the size distribution and chemical composition of the sampled ambient aerosols. Furthermore, labile constituents of fine particles, such as volatile ammonium nitrate are preserved during this process.

Local deposition efficiencies and deposition patterns of aerosol particles were studied experimentally in single bifurcation tube models with varying geometry. The diameter ratio (DR) of the daughter to parent tube was varied from 0.64 to 1.0 and a local obstruction was also imposed in some of the models. Monodispersed oil particles (size range =3–7 μm dia.) tagged with uranine were generated as test aerosols and were drawn through the model at flow rates corresponding to Reynolds number (Re) of 283–3397. It was found that deposition of particles took place mainly on and in the immediate vicinity of the bifurcation ridge for Stokes number (Stk) ≥0.03 regardless of tube geometries used. Deposition efficiency (DE) in the bifurcation region increased with increasing Stk but did not change with branching angles between 30° and 45°. The diameter ratio showed only a minor effect on DE. The results suggest that Stk may be the single most important factor for particle deposition in the bifurcating airways in the inertial regime.

Response of two commercial quartz crystal aerosol mass monitor (TSI Model 3200A and 3500) to several sulfate and nitrate aerosols has been examined in terms of linerity, mass sensitivity and hygroscopicity. For all the aerosols tested, the mass monitor responded linearly (± 15% variation) to mass loadings on the sensing crystal up to an accumulated frequency change of 1000 Hz in Model 3200A and 4000 Hz in Model 3500. Within this linearity limit, the mass sensitivity tended to increase gradually with increase of mass loading. The mass sensitivity coefficient (S) of the monitor varied from 135 to 219 Hz/μg with 0.5 μm MMAD (GSD = 1.5) aerosols, depending upon the kind of aerosols and was 10–26% higher with 1.2 μm MMAD aerosols. The monitors responded sensitively and correctly to hygroscopic nature of the aerosols tested. showing sharp increases of frequency change at known deliquescent points of the aerosols.

Deposition of aerosol particles in a straight tube with an abrupt local obstruction was determined experimentally in model tubes with tube Re ranged between 140 and 2800. Various types of obstruction whose hydraulic throat diameters ranged between 0.22 and 0.25 cm were created locally in the middle of smooth 0.5 cm i.d. glass tubes. Aerosol deposition occurred mostly behind the obstruction within a distance equalling 10 tube diameters. The deposition in this segment was increased rapidly with increasing flow rate and reached up to more than 100 times greater for particles of 3.1 γm diameter than in the unobstructed tube. The deposition increased with increasing particle size and was well correlated with pressure drop across the obstruction regardless of the types of obstruction. Stokes number (Stk) represented the deposition only for a specific type of obstruction. Despite the difference in flow structure, the deposition behind the obstruction was well correlated with deposition parameters used for fully developed turbulent pipe flow, dimensionless deposition velocity and relaxation time and agreed closely with turbulent deposition in a rough pipe.