Y. S. Cheng

Performance of a TSI Aerodynamic Particle Sizer

Calibration curves of the aerodynamic particle sizer (APS) under different sets of operating conditions (i.e., pressure drop across the nozzle, flow rate, and ambient pressure) were obtained. Materials used included oleic acid (OA), dioctyl phthalate (DOP), polystyrene latex (PSL), and fused aluminosilicate particles (FAP). The effect of particle density on the calibration was not found to be significant among test aerosols (in the density range from 0.89 to 2.3 g/cm3). Calibration curves obtained at reduced ambient pressure were different from the manufacturers curve, indicating that recalibration of the APS is required if other than standard operating conditions are used. However, all the curves can be consolidated into a unique curve that relates the Stokes number at the nozzle exit to the normalized particle velocity (particle velocity divided by gas velocity). Methods for calculating gas velocity, particle velocity, and other pertinent parameters for the APS were developed and the results are presen...

Characterization of Diesel Exhaust in a Chronic Inhalation Study

We describe characterization of the exposure atmosphere in a life-span study of rats and mice exposed to chronic inhalation of diluted diesel exhaust. Diesel exhaust was generated by one of two General Motors 1980 Model, 5.7-liter V8 diesel engines connected to an eddy current dynamometer/flywheel system and operated on the Federal Test Procedure urban driving cycle. Animals were exposed 7 hours/day, 5 days/week to exhaust at particle concentrations of approximately 7000, 3500, and 350 micrograms/m3 or to clean air. Throughout the 24-month study, the mean particle mass concentration remained within 5% of the target values. Measured gas concentrations of CO, CO2, NO, NO2, and hydrocarbons were roughly proportional to the dilution ratio. A combination of a Lovelace Multijet cascade impactor followed by a parallel flow diffusion battery gave mass median diameters of 0.23 to 0.26 microns averaged over complete cycles and geometric standard deviations larger than 4. The aerosol concentration profile was associated with the operating cycle. The measured diesel particle size was similar to previously reported values of particles released to the atmosphere from the same model engine.

Collection efficiencies of a point-to-plane electrostatic precipitator

Collection efficiencies of a point-to-plane electrostatic precipitator were evaluated as functions of particle size, aerosol flow and ion current. Monodisperse aerosols ranging from 0.03 to 2.0 μm were used. Collection efficiencies decrease with 1) an increase of aerosol flow rate, 2) a decrease of particle size and 3) an increase of ion current. At the lowest tested flow, 100 cm3min, the effects of ion current and particle size seem to be minimal. Average efficiencies were found to be 90, 85 and 85% over the entire particle size range used in this study, for ion currents of 1.0, 3.5 and 5.0 microamperes respectively.

Performance of a Modified Virtual Impactor

The performance of a modified virtual impactor with a clean air core in the center of an aerosol flow is described. With this feature, the modified virtual impactor has overcome the inherent disadvantage of conventional designs which have fine particle contamination in the coarse particle fraction. Furthermore, the separation efficiency of this impactor can be predicted from the efficiency curve of the conventional type virtual impactor and the ratio of clean air flow to the total flow rate. With a higher clean air flow, the 50% cutoff Stokes number slightly increases and the efficiency curve has better separation characteristics. Internal wall losses in the impactor are a function of particle size and reach a local maximum near the 50% cutoff size.

A Study of Density Effect and Droplet Deformation in the TSI Aerodynamic Particle Sizer

Effects of particle density and droplet deformation on the performance of a TSI aerodynamic particle sizer (APS) were studied using polystyrene latex (PSL), dioctyl phthalate (DOP), ammonium fluorescein (AF), fused aluminosilicate (FAP), and fused cerium oxide (FCO) monodisperse aerosols. Results indicated that, because of the sensitivity of the instrument, periodic cleaning of the APS inner nozzle is needed to maintain the consistency of its calibration curve. Density effects were experimentally confirmed with PSL, AF, FAP, and FCO aerosols of particle densities ranging from 1.05 to 4.33 g/cm3. Results, however, showed that this effect can only be experimentally detected for particles of density greater than 2 g/cm3 and aerodynamic diameter greater than 5 (μm. Effects of droplet deformation were studied with DOP.

Evaluation of an Environmental Reaction Chamber

A cylindrical, Pyrex glass chamber with stable temperature control was evaluated to determine the residence time of aerosol particles within an enclosure, and to compare our results to the theoretical expression derived by Crump and Seinfeld (1981). Monodisperse polystyrene latex particles with diameters between 0.04 and 3 μm were used to determine the particle deposition rates under different water temperature gradients (δTw) between the top and bottom water layers of the chamber. The water layers and an insulating fiberglass jacket around the side wall helped to maintain a steady temperature gradient in the chamber and this was found to be very important in controlling particle deposition. Results indicated that the minimal deposition losses occurred at δTw = 0°C for particles between 0.2 and 0.3 μm, with a residence time as long as 38 h. Results also showed that particle deposition rate can be described by the theory of Crump and Seinfeld with an exponent n = 2.02 and a turbulence intensity k e = 0.003...

Counting Efficiency of the TSI Model 3020 Condensation Nucleus Counter

The counting efficiency of the TSI model 3020 condensation nucleus counter (CNC) was determined as a function of aerosol flow rate and trigger level using aerosols of known size and an aerosol electrometer. When the aerosol flow rate dropped from 300 to 200 mL/min, counting efficiencies increased significantly in the single-particle counting mode for particles with diameter 20 nm increased and exceeded unity. When the aerosol flow rate was reduced to 100 mL/min, the counting efficiencies for both counting modes decreased regardless of particle size. Varying the trigger level of the CNC did not influence the photometric mode counting efficiency. However, the counting efficiency of the single-particle counting mode increased with decreasing trigger level, especially for particles < 20 nm in diameter. Characteristics for individual instruments need to be measured because...

The effect of exposure pattern on the accumulation of particles and the response of the lung to inhaled particles

We hypothesized that a rapid rate of delivery of particles to the lung would overwhelm the normal clearance mechanisms of the lung and result in a higher lung burden of particles and a greater inflammatory response than a slower rate of particle delivery. F344/N rats were exposed over a 12-week period to the same weekly concentration times time product of carbon black (CB) particles, but at three different exposure rates: 3.5 mg/m3, 16 hr/day, 7 days/week; 13 mg/m3, 6 hr/day, 5 days/week; or 98 mg/m3, 4 hr/day, 1 day/week. The intermediate exposure rate was chosen to mimic an occupational work week and to give an 8-hr, time-weighted average exposure equal to the threshold limit value (TLV) for nuisance dusts of the American College of Governmental Industrial Hygienists (10 mg/m3). Pure CB has a lower TLV, 3.5 mg/m3, than nuisance dusts, but this is based on avoidance of excessive dirtiness in the workplace, not on the toxicity of CB. Lung burdens of CB were measured after 3, 6, 9, and 12 weeks of exposure and at 4, 8, 12, 16, and 24 weeks after the exposure ended. The inflammatory response was quantified by analysis of bronchoalveolar lavage fluid (BALF) after 6 and 12 weeks of exposure and at 1, 12, and 24 weeks after exposure. The histopathology of the lung was evaluated at the end of the exposure and at 24 weeks after the exposure. Acquired lung burdens were between 3 and 4 mg/lung at the end of the exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

The Fate of Inhaled Azodicarbonamide in Rats

Azodicarbonamide (ADA) is widely used as a blowing agent in the manufacture of expanded foam plastics, as an aging and bleaching agent in flour, and as a bread dough conditioner. Human exposures have been reported during manufacture as well as during use. Groups of male F344/N rats were administered ADA by gavage, by intratracheal instillation, and by inhalation exposure to determine the disposition and modes of excretion of ADA and its metabolites. At 72 hr following gavage, 30% of the administered ADA was absorbed whereas following intratracheal instillation, absorption was 90%. Comparison between groups of rats exposed by inhalation to ADA to achieve body burdens of 24 or 1230 micrograms showed no significant differences in modes or rates of excretion of [14C]ADA equivalents. ADA was readily converted to biurea under physiological conditions and biurea was the only 14C-labeled compound present in excreta. [14C]ADA equivalents were present in all examined tissues immediately after inhalation exposure, and clearance half-times on the order of 1 day were evident for all tissues investigated. Storage depots for [14C]ADA equivalents were not observed. The rate of buildup of [14C]ADA equivalents in blood was linearly related to the lung content as measured from rats withdrawn at selected times during a 6-hr inhalation exposure at an aerosol concentration of 25 micrograms ADA/liter. In a study extending 102 days after exposure, retention of [14C]ADA equivalents in tissues was described by a two-component negative exponential function. The results from this study indicate that upon inhalation, ADA is rapidly converted to biurea and that biurea is then eliminated rapidly from all tissues with the majority of the elimination via the urine.

Effect of Vapor Concentration on the Disposition of Inhaled 2,3-Dichloropropene in Fischer-344 Rats

2,3-Dichloropropene (DCP) is an intermediate used in the manufacture of carbamate herbicides and there is potential for human exposure during the manufacturing process. DCP is a known mutagen in bacteria systems and some structural analogs of DCP are carcinogenic. Since little is known about the disposition of DCP in animals after inhalation, studies were conducted in male Fischer-344 rats to determine the effect of vapor concentration on absorption and excretion. Uptake and elimination of 14C was studied in rats after nose-only inhalation of 17, 240, or 1650 nmol of [14C]DCP vapor/liter of air (0.4, 6, or 40 ppm, respectively, at 760 mm and 25 degrees C) for 6 hr. The percentage of inhaled DCP absorbed averaged 38% and was not statistically different at any vapor concentration, although minute volume was lower during exposure to 1650 nmol/liter. Urine, feces, and expired air were collected from rats for 65 hr after exposure. Rats were sacrificed and tissues, carcass, excreta, and expired air were analyzed for 14C. Routes of 14C excretion were independent of vapor concentration, with 50% of the 14C excreted in urine, 13% in feces, approximately 7% as CO2, and less than 1% as DCP in expired air. Rates of 14C excretion were also independent of vapor concentration, with the half-times averaging 9.9 hr (urine), 13.6 hr (feces), and 0.9 hr (14CO2). Sixty hours after inhalation, 29% of the initial body burden of 14C remained in the carcass. Most was associated with the pelt, but some 14C was found in all tissues. Respiratory tract, GI tract, liver, and kidney were tissues with the highest 14C contents. The results indicate that DCP metabolism and excretion rates are relatively constant throughout the vapor concentration range studied. This suggests that results from more detailed pharmacokinetic studies (and possibly toxicity studies) at one DCP concentration may be extrapolated to other concentrations within this range.