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PubMed2000

Analysis and simulation of wintertime light scattering by the urban aerosol in Dallas-Fort Worth.

Wintertime atmospheric light scattering in Dallas, TX, was estimated through the use of aerosol models. Input data for the aerosol models were provided by measurements of aerosol chemistry, physical particle size distributions, and distributions of particulate sulfur by particle size, and by predictions by an atmospheric simulation model. Light scattering measurements provided a basis for testing the aerosol models. The SCAPE thermodynamic equilibrium model was used to estimate the amount of liquid water associated with particles and the ELSIE Mie scattering model was applied to estimate the resulting light scattering. The calculations were based on aerosol properties measured in Dallas during December 1994 and February 1995, and changes in scattering due to hypothetical changes in the aerosol were predicted. The predicted light scattering was compared to scattering measured by an Optec nephelometer; agreement was within 20% in every case.

Aerosols↗
PubMed2005

Effects of aerosol species on atmospheric visibility in Kaohsiung City, Taiwan.

Visibility data collected from Kaohsiung City, Taiwan, for the past two decades indicated that the air pollutants have significantly degraded visibility in recent years. During our study period, the seasonal mean visibilities in spring, summer, fall, and winter were only 5.4, 9.1, 8.2, and 3.4 km, respectively. To ascertain how urban aerosols influence the visibility, we conducted concurrent visibility monitoring and aerosol sampling in 1999 to identify the principal causes of visibility impairments in the region. In this study, ambient aerosols were sampled and analyzed for 11 constituents, including water-soluble ions and carbon materials, to investigate the chemical composition of Kaohsiung aerosols. Stepwise regression method was used to correlate the impact of aerosol species on visibility impairments. Both seasonal and diurnal variation patterns were found from the monitoring of visibility. Our results showed that light scattering was attributed primarily to aerosols with sizes that range from 0.26 to 0.90 pm, corresponding with the wavelength region of visible light, which accounted for approximately 72% of the light scattering coefficient. Sulfate was a dominant component that affected both the light scattering coefficient and the visibility in the region. On average, (NH4)2SO4, NH4NO3, total carbon, and fine particulate matter (PM2.5)-remainder contributed 53%, 17%, 16%, and 14% to total light scattering, respectively. An empirical regression model of visibility based on sulfate, elemental carbon, and humidity was developed, and the comparison indicated that visibility in an urban area could be properly simulated by the equation derived herein.

Aerosols↗
PubMedDate not supplied

Computation of ammonium bisulfate aerosol deposition in conducting airways.

Experimental measurements of the growth of monodisperse dry NH4HSO4 aerosols by H2O vapor condensation have been reported in the literature. These data are incorporated into an aerosol deposition model to study the behavior of inhaled NH4HSO4 particles, which is of concern in relation to human health. The tracheobronchial tree is described by Weibel's model A morphology, and Landahl's formulas are used to compute particle deposition efficiencies. Enhanced losses in the trachea due to the action of the laryngeal jet are accounted for by using an empirical deposition efficiency equation. The effect of NH4HSO4 aerosol growth is quantitated by comparisons of total and intrabronchial deposition probabilities with those of a nonhygroscopic aerosol of equal aerodynamic size. Computations indicate that hygroscopic growth effects are a function of the size of the particles inhaled. Total deposition efficiencies of NH4HSO4-H2O droplet aerosols are greater than those of nonhygroscopic aerosols only if the former originate from dry NH4HSO4 particles exceeding a critical geometric diamter of 0.3 micrometer. Growth effects are explained in terms of the relative efficiencies of the dominant deposition mechanisms active in the lung.

Aerosols↗
PubMed1991

Effects of exposure to sulfate aerosols and antigen on breathing curve patterns of guinea pigs.

We investigated the effects of ammonium sulfate aerosols on asthmatic dyspnea (immediate type) induced by repeated inhalation of a mixture of bovine serum and egg albumin and on the nonspecific responsiveness of the airway tract to acetylcholine. Guinea pigs were exposed to sulfate aerosol in concentrations of 0.2, 0.4, and 2.0 mg/m3 and to 0.2 mg/m3 sulfate aerosol combined with 0.1 ppm of SO2. The exposure time was 2 h/d, 5 d/wk, 38 times in all. The animals were successively exposed to aerosol (for 2 h) and, after 30 min, to the spraying of albumin solution 3 times per week, 7 or 9 times in all. Breathing curves were continuously recorded by a body plethysmograph system during the sensitization periods. The experiments showed that the degree of asthmatic dyspnea in guinea pigs was increased by the exposure to aerosol, and that there is a quantitative relation between the severity of the dyspnea and extent of the exposure. Exposure in the combination with SO2 showed no effect at the concentration studied. Following the exposure experiment, each group of animals was exposed to the spraying of acetylcholine. The sensitivity to acetylcholine increased at aerosol concentrations of 0.4 and 2.0 mg/m3.

Acetylcholine↗
PubMed1993

Whole body exposures to a phosphoric acids aerosol: I. Spontaneous activity effects in wild rodent and avian species.

Two inhalation-chamber studies were conducted to assess acute (2-h out-of-chamber) and subacute (< or = 6 d postexposure) spontaneous activity effects of whole-body phosphoric acids aerosol exposure(s) in black-tailed prairie dogs (Cynomys ludovicianus) and rock doves (Columba livia). The aerosol was generated using a red phosphorus/butyl rubber (RP/BR) mixture under development as a military obscurant. Each study involved (1) 3 RP/BR target concentration groups [0.0 (controls), 1.0, and 4.0 mg/L], (2) 24 prairie dogs or rock doves (8/group), with gender included as a factor, (3) a successive 3-phase paradigm (2 d preexposure; 4 and 2 d of about 80 min/d exposures to RP/BR for prairie dogs and rock doves, respectively; and 6 d postexposure), and (4) infrared detection of the rodents'/birds' home-cage movements. In-chamber atmospheres were uniform and acceptable for all exposures; median aerosol mass concentrations ranged from 0.76 to 0.89 mg/L and 3.46 to 3.74 mg/L for the 1.0 and 4.0 mg/L groups, respectively, with median phosphoric acid (H3PO4) readings of between 67.2 and 74.3%; median particles were < or = 0.85 microns. Mortality was negligible; no prairie dogs died, but 1 male rock dove died on d 3 postexposure to two 4.0 mg/L target concentrations of RP/BR aerosol. Group x session interactions were significant for the acute activity counts of both species. The acute mean ambulatory (e.g., walking) counts of prairie dogs and the acute mean ambulatory and horizontal (e.g., preening) counts of rock doves exposed to 4.0 mg/L RP/BR aerosol were relatively less than those of the other groups after the first 2 or 1 exposures, respectively. Nevertheless, acute session means for all groups approximated or exceeded the 23 h/d activity measured during the pre- and postexposure phases--data indicating that chamber confinement caused a temporary, sharp increase in activity for both species irrespective of RP/BR aerosol concentrations. No RP/BR concentration-related, subacute shifts in the activity of the rodents/birds were observed.

Administration, Inhalation↗
PubMed1993

Whole-body exposures to a phosphoric acids aerosol: II. Food/water/weight effects in wild rodent and avian species.

Separate inhalation-chamber studies were conducted to assess acute/subacute food intake (g), water intake (ml), and body weight (g) effects of four whole-body phosphoric-acids-aerosol exposures in black-tailed prairie dogs (Cynomys ludovicianus); subacute effects of two exposures were studied in rock doves (Columba livia). A 95% red phosphorus/5% butyl rubber (RP/BR) mixture was burned to produce the aerosol. Each study involved (1) 3 RP/BR target concentration groups (0.0, 1.0, and 4.0 mg/L), (2) 24 prairie dogs or doves (8/group), with gender included as a factor in each study, and (3) a successive 3-phase paradigm (2 d preexposure; 4 and 2 d of approximately 80 min/d exposures to RP/BR for prairie dogs and rock doves, respectively; and 6 d postexposure). Results showed that in-chamber atmospheres were uniform and acceptable for all exposures. No prairie dogs died, but 1 male rock dove died on d 3 postexposure to 4.0 mg/L aerosol. Concentration and gender main effects were significant for the acute (2 h out-of-chamber) food intake, water intake, and weight change of prairie dogs, with aerosol-exposed and male rodents showing decrements. Gender and day main effects were also significant for the subacute (23 h/d) variables in prairie dogs; females weighted less than males, and reduced food/water/weight was evident for all animals during the 4 exposure days and first 3 postexposure days. For rock doves, subacute gender and day main effects, plus concentration x day and concentration x gender x day interactions, characterized the data. A transitive relationship was evident among RP/BR aerosol conditions (0.0 < 1.0 < 4.0 mg/L) and mean decreased food intakes on the exposure days (d2 < d1). Enhanced postexposure water replenishment by female versus male doves exposed to 4.0 mg/L RP/BR aerosol was a main finding. Results are explained based upon a temporal model of phosphoric acid caused ulcers/edema. Effects are compared to prior evidence for albino rats, prairie dogs and rock doves; these are also discussed relative to certain human health and ecotoxicological literature.

Aerosols↗
PubMedDate not supplied

Construction and evaluation of an aerosol generating apparatus for combustion products from polyurethane foam.

A system has been constructed and evaluated for generating aerosols from combustion or pyrolysis of various cross-linked polymers. The system consists of an aerosol generator and an aerosol chamber with a sampling compartment designed for various samplers and sampling probes. A geared electric motor assembly is used to lower a polymer strip into the controlled atmosphere of a quartz-lined furnace. The polymer used in this investigation was a polyurethane foam (PUF) based on toluene diisocyanate (TDI). Combustion of the PUF was conducted in filtered air at a temperature of 300 degrees C. The particle number concentration of the generated aerosol was measured by light scattering in the particle size range from 0.1 micron to greater than 5 microns. Air samples were collected periodically in impinger flasks using dibutylamine (DBA) in toluene as derivatization reagent. The TDI-DBA derivatives from the impinger samples were analyzed with high performance liquid chromatography. The aerosol generating system was found to generate a stable, reproducible, and predictable concentration of particles and TDI monomer. Three partial least squares models were created to evaluate the generator. The investigated responses were the TDI concentration, the particle number concentration, and the stability of the particle number concentration during the generating process. The factor with most impact on the concentrations of the generated aerosol was found to be the interaction between linear feeding rate of the polymer strip and the flow rate of combustion gas. For stability the linear feeding rate was the most important.

Aerosols↗
PubMed1979

Generation and characterization of condensation aerosols of vanadium pentoxide and pyrene.

Generation and characterization of submicron aerosols of V2O5 and pyrene, two materials with very different physicochemical properties, were studied. Vaporization-condensation methods were used to generate the aerosols. The effects of various experimental conditions on particle size and aerosol mass concentration were investigated. Also, chemical stability of the aerosols and the source materials with respect to temperature was determined. Experimental results show that there are significant differences in the nature of pyrene and V2O5 aerosols. These methods and experimental conditions can be easily adapted for generation of heterogeneous condensation aerosols of pyrene and V2O5.

Aerosols↗
PubMed1983

Monitoring real-time aerosol distribution in the breathing zone.

A prototype air sampling, data recording, and data retrieval system was developed for monitoring aerosol concentrations in a worker's breathing zone. Three continuous-reading, light-scattering aerosol monitors and a tape recorder were incorporated into a specially designed and fabricated backpack for detailed field monitoring of both temporal and spatial variability in aerosol concentrations within the breathing zone. The backpack was worn by workers in a beryllium refinery. The aerosol which passed through each monitor was collected on a back-up filter for later chemical analysis for Be and Cu. The aerosol concentrations were recorded on magnetic tape as a function of time. The recorded signals were subsequently transcribed onto a strip chart recorder, then evaluated using a microcomputer with graphics capability. Field measurements made of the aerosol concentration at the forehead, nose, and lapel of operators during the melting and casting of beryllium-copper alloy demonstrated that there is considerable variability in concentration at different locations within the breathing zone. They also showed that operations resulting in worker exposure can be identified, and the precise time and duration of exposure can be determined.

Aerosols↗
PubMed1983

Aerosol rebreathing method for assessment of airway abnormalities: theoretical analysis and validation.

An aerosol rebreathing method which determines total aerosol deposition in the lung by rebreathing non-radioactive inert aerosol was investigated theoretically for its performance characteristics. The method was then validated experimentally by examining a system response to various operating parameters, its reproducibility and convenience in clinical use. It was found from the theoretical analysis that an optimum performance would be achieved by breathing an aerosol of particles 1 micrometer in diameter with a 500-cm3 tidal volume at the breathing rate of 30 breaths/min. With these optimum parameters, experimental results of 10 normals and 10 patients with obstructive airway disease revealed an excellent measurement reproducibility within subjects (+/- 10% from means). There was a wide separation between the two groups in terms of number of rebreathing breaths to reach 90% aerosol deposition (N90) (mean +/- S.E. = 10.8 +/- 1.6 for normals vs. 3.9 +/- 1.1 for patients) and cumulative percentage of aerosol deposition at the fourth breath (AD4) (mean +/- S.E. = 68 +/- 4.4% for normals vs. 90 +/- 3.5% for patients).

Adult↗
PubMed1983

Attempts at aerosol control in a turkey rearing confinement with negative air ionization.

Aerosol control is a significant problem in agriculture and industry. Two separate studies were conducted to determine the effectiveness of a "negative air ionization" system in aerosol control. The first study was conducted with a turkey "brooder" barn and a control for a six-week period. The second study was conducted with a turkey "grow-out" barn and a control for a twelve-week period. Sampling parameters for both studies included environmental aerosol sampling, ion imbalance measurements, relative humidity, temperature and barometric pressure measurements and daily turkey mortality. Study two also included post study bird weights. Results of sampling parameters were consistent between study one and study two. No significant difference was found between test and control total average aerosol concentration for both studies. Ion imbalance measurements served to indicate that test environments were negatively ionized while control environments experienced normal environmental conditions. Meteorological parameters did not significantly affect aerosol concentrations. Normal variations in bird mortality were observed in the first study, but death rates increased with ionization in the latter. Overall, it was determined that the "negative air ionization" could not be considered as an effective means of aerosol control in turkey rearing confinements.

Aerosols↗
PubMed1987

The effect of aerosol size distribution and measurement method on respirator fit.

The particle size-dependent leakage into a respirator was examined by measuring the leakage of particle sizes between 0.07 to 4.4 microns through three hole sizes in a negative-pressure half-mask respirator worn by a human subject. This investigation showed that the size distribution of an aerosol test agent and the measurement method have an effect on the leakage measured in a quantitative fit test. For instance, the ratio of percent leakage measured by light scattering between test aerosols with count median diameters of 2.2 and 0.28 microns can be as large at 5:1. Likewise, the ratio of the percent leakage measured by a particle count method vs. a mass method of detection of the same polydisperse aerosol with a count median diameter equal to 2.2 microns can be as high as 4:1. The mass leakage into a mask with a leak is also greater for an exposure aerosol with a count median diameter between 0.15 to 0.30 micron compared to exposure aerosols with larger count median diameters for aerosols with the same mass concentration.

Aerosols↗
PubMed1988

Experiments supporting the use of ambient aerosols for quantitative respirator fit testing.

Most methods for testing facial seal leakage on subjects undergoing respirator fit tests involve comparing the generated aerosol particulate concentration inside the subject's respirator to the concentration in a test chamber. These aerosols are produced by fogging substances such as corn oil, dioctyl sebacate, or dioctyl phthalate (DOP) into the test chamber. The health effects of these substances and of their aerosols on respiratory systems are uncertain. The proposed alternate method uses as a test medium ambient particles which exist in most room atmospheres. The proposed method eliminates the need for a test chamber and for an intentionally produced aerosol. The subject is tested for respirator inleakage by comparing the particulate count concentration inside the subject's respirator to that of the room atmosphere outside the respirator. This method is less expensive and simpler to administer than the use of oil or other deliberately produced aerosols because it uses an existing ambient test medium. Statistical analysis of the test data indicates favorable comparison with the conventional chamber-aerosol method.

Aerosols↗
PubMed1997

Comparison of methods for personal sampling of inhalable and total lead and cadmium-containing aerosols in a primary lead smelter.

It has been proposed that future occupational aerosol exposure standards be based on particle size-selective sampling criteria that more accurately reflect worker exposure. In relation to methods currently used for determining individual workers' lead exposures, the widely used 37-mm, closed-face, plastic sampling cassette is known from laboratory wind tunnel studies to undersample significantly compared with estimations of aerosol actually inhaled, especially for large particles. The present study investigated the degree to which this is borne out in field sampling by using side-by-side sampling in selected work sites in a primary lead smelter. Exposures to "total" airborne lead and cadmium as measured using the 37-mm sampler (E37) were compared with exposure measurements using the institute of Occupational Medicine (IOM) personal inhalable aerosol sampler (EIOM). There were 166 good sample pairs for lead and 55 for cadmium. The ratio (reflecting the fractional undersampling of the 37-mm sampler, as represented by the ratio EIOM/E37) was consistently greater than unity, by factors obtained by regression analysis ranging (for different parts of the plant) from 1.39 to 2.14 for lead and 1.29 to 2.12 for cadmium. The factor tended to be greater for parts of the plant characterized by coarser aerosol, consistent with the physical sampling characteristics of the two instruments. This research is important (1) in assessing the impact of implementation of new standards for lead- and cadmium-containing aerosols in the primary lead production industry, and (2) in the development of new occupational exposure limits based on the inhalable aerosol fraction.

Aerosols↗
PubMed1997

Characteristics of lead aerosols in different work environments.

Air samples were collected to examine physical and chemical characteristics of lead aerosols in different work environments in the airborne lead concentration range from 28-783 micrograms/m3. Size distribution of aerosols was measured using a Marple personal cascade impactor, and lead analysis was conducted using graphite atomic absorption spectrometry. Lead aerosol size distribution was found to be different from that of total particles. Such differences are not negligible and must be taken into account when estimating aerosol deposition within the human respiratory tract. Variation of MMAD (mass median aerodynamic diameter) and GSD (geometric standard deviation) of lead aerosols in the coarse mode wit total airborne concentration was found to be small, and the assumption that lead aerosol distribution is constant is reasonable for establishing the relationship between airborne lead concentration in all work areas of the three plants except the charging area of the capacitor plant. Therefore, it is expected that either total airborne lead or respirable airborne lead concentration can be used to correlate blood lead concentration.

Aerosols↗
PubMed1998

Aerosol-induced immunoglobulin (Ig)-E unresponsiveness to ovalbumin does not require CD8+ or T cell receptor (TCR)-gamma/delta+ T cells or interferon (IFN)-gamma in a murine model of allergen sensitization.

Mice exposed for 20 min daily to aerosolized ovalbumin (OVA) for 10 d at concentrations from 1 to 0.01% OVA made greatly reduced immunoglobulin (Ig)-E responses to subsequent immunogenic OVA challenges, given either intraperitoneally or by aerosol. This IgE-specific unresponsiveness lasted for at least four months. However, these aerosol-treated mice were primed for larger OVA-specific IgG1 and IgG2a responses. The specific reduction in IgE responses was not due to preferential induction of a T helper (Th)-1 response as aerosol OVA- primed mice made greatly reduced Th2 and no detectable Th1 response after rechallenge in vitro. Consistent with this, the increase in circulating eosinophils observed in control Th2-primed mice was absent in aerosol OVA-treated animals. Interferon (IFN)-gamma was not required for this unresponsiveness, as IFN-gamma knockout mice and anti-IFN-gamma antibody-treated wild-type mice had greatly reduced levels of IgE similar to wild-type controls. CD8+ T cells played a relatively small role as IgE responses were reduced to about the same extent in beta2 microglobulin-deficient, or in anti-CD8-treated wild-type mice as in normal mice after aerosol OVA treatment. Similarly, T cell receptor (TCR)-gamma/delta T cells were not required for maximal inhibition of the IgE response. These results demonstrate that exposure to inhaled protein antigens can induce a state of unresponsiveness of CD4+ T cells that results in a prolonged loss of IgE and eosinophil responses to subsequent challenges. This T cell unresponsiveness was shown not to require CD8+ or TCR-gamma/delta+ T cells or IFN-gamma.

Aerosols↗
PubMed1995

Efficacy of portable filtration units in reducing aerosolized particles in the size range of Mycobacterium tuberculosis.

OBJECTIVE: To evaluate engineering control measures to prevent nosocomial transmission of diseases such as tuberculosis, we studied four portable high-efficiency air filtration units, including three high-efficiency particulate air (HEPA) filtration units, for their ability to remove aerosolized particles. DESIGN: Studies were conducted in either a nonventilated aerosol chamber or in a hospital isolation room that met CDC guidelines for TB control (negative pressure, > or = 6 air changes per hour, air exhausted directly to the outside). The rooms were challenged with aerosolized mineral oil in the size range of 0.3 to 5.0 microns at levels 10 to 20 times the normal airborne particle load in the room at baseline. Airborne particles were counted with a laser counter capable of simultaneously measuring sizes > or = 0.3, > or = 0.5, > or = 1.0, and > or = 5.0 microns. Experimental runs were conducted with the filtration units in the center or corner of the chamber or room, and the particle counter in the center of the room or at the exhaust vent. RESULTS: Portable filtration units were effective in accelerating the removal of aerosolized submicron particles. In the nonventilated room, time required by the various portable filtration units for removal of 90% of aerosolized particles (> or = 0.3 microns) ranged from a low of 5 to 6 minutes to a high of 18 to 31 minutes, compared to the control (no filtration unit), > 171 minutes. In the hospital room, individual filtration units removed 90% of aerosolized particles (> or = 0.3 microns) in times ranging from 5 to 8 minutes to 9 to 12 minutes, compared to the control (no filtration unit), 12 to 16 minutes. The location of the portable filtration unit (center versus corner) did not affect the clearance rate of airborne particles. CONCLUSION: Our data indicate that portable filtration units can rapidly reduce levels of airborne particles similar in size to infectious droplet nuclei and, therefore, may aid in reducing the risk of tuberculosis exposure.

Aerosols↗
PubMed1994

Modelling the effect of charge on selective deposition of particles in a diseased lung using aerosol boli.

The technique of using a charged bolus of aerosol to deliver a drug or other agent is advantageous since sites of interest within the lung can be selectively targeted. Ideally, the volume of the bolus should match that of the targeted region allowing the aerosol bolus particles to be confined to the selected area during the pause period after inhalation. Our existing computer model for predicting the deposition of charged aerosol particles has been developed to encompass aerosol boli, some diseased lung morphologies and drug dose administered per breathing cycle. Aerosol deposition in the targeted region is found to be enhanced by increasing particle charge, pause period and particle size. For particles in the size range 1-2.5 microm, aerosol deposition in the region affected by bronchoconstriction does not alter significantly with flow rate variation (range 250-1000 ml s(-1)) for a targeted charged bolus of matched volume. The technique may enable the optimal delivery of therapeutic or other agents to diseased or normal lungs.

Administration, Inhalation↗