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PubMed2006

The effect of film thickness on thermal aerosol generation.

PURPOSE: Rapid heating of thin films of pharmaceutical compounds can vaporize the molecules, which leads to formation of aerosol particles of optimal size for pulmonary drug delivery. The aim of this work was to assess the effect of coated film thickness on the purity of a thermally generated (condensation) drug aerosol. MATERIALS AND METHODS: Pharmaceuticals in their free base form were spray-coated onto stainless steel foils and subsequently heated and vaporized in airflow via a rapid resistive heating of the foil. Aerosol particles were collected on filters, extracted, and analyzed using reverse phase HPLC to assess the amount of degradation induced during the vaporization process. RESULTS: Condensation aerosols of five pharmaceuticals were formed from a wide range of film coating thicknesses. All five showed a roughly linear trend of increasing aerosol purity with decreasing film thickness, although with quite different slopes. These findings are consistent with a model based on general vaporization and degradation kinetics. Small non-uniformities in the film do not significantly alter aerosol purity. CONCLUSIONS: Rapid vaporization of pharmaceuticals coated as thin films on substrates is an efficient way of generating drug aerosols. By controlling the film thickness, the amount of aerosol decomposition can be minimized to produce high purity aerosols.

Aerosols↗
PubMed1987

Blockade of 'alveolar' and airway reflexes by local anesthetic aerosol in dogs.

To determine whether local anesthetic aerosol could selectively block a reflex thought to originate from the alveoli, two small particle bupivacaine aerosols (mass median diameters 1.0 and 1.7 micron) were administered on separate occasions to spontaneously breathing anesthetized dogs. Both aerosols resulted in a small but statistically significant increase in VT and one produced an increase in f. The pulmonary chemoreflex to right heart injection of capsaicin, the cough reflex and the Hering-Breuer inflation reflex were unaffected. The ability of a large particle aerosol (mass median diameter 4.8 micron) to block these reflexes was also assessed. This aerosol produced a progressive slowing and deepening of breathing which was maximal after 20 min of aerosol inhalation. Ten min of this aerosol attenuated the pulmonary chemoreflex and abolished the cough and inflation reflexes; 20 min abolished all reflexes. These had recovered by about 1 h after aerosol. Intravenous bupivacaine had no effect on breathing or any reflex. We conclude that a local anesthetic aerosol can block reflexes arising from the alveoli, but not selectively.

Aerosols↗
PubMed1989

Direct write-out of particle size distribution of inhaled aerosol deposition using a laser scattering method.

We developed a device to measure inhaled aerosol deposition in the lung from the difference in particle size distribution of the aerosol during inspiration and expiration. To measure quantity and size distribution of nebulized aerosol particles directly at the subject's mouth we used a He-Ne gas laser scattering technique. To test the reliability of the instrument, we measured particle size distributions of saline aerosols generated by four kinds of nebulizer and compared the results with those from a Malvern 2600D particle sizer as a standard of comparison. Measured mass median diameters (MMDs) were almost identical by both methods. Aerosol deposition in five normal subjects showed that the deposition fraction of the particles increased the larger the particle sizes inhaled. The data suggest that the newly developed aerosol spectrometer can directly analyze aerosol particle size distribution at the mouth during tidal breathing, and that the instrument is useful for quantitative analysis of aerosol inhaled and of inhaled aerosol deposition.

Aerosols↗
PubMed1986

Acute inhalation toxicopathology of lithium combustion aerosols in rats.

Male and female F344/Lov rats were exposed to aerosols produced by burning lithium metal under conditions designed to stimulate a fire in the containment building of a fusion reactor. Lithium combustion aerosols were generated by sweeping lithium vapor into air atmospheres with controlled CO2 and H2O concentrations. Chemical analyses of the aerosols produced indicated a dependence of the chemical form of carbon dioxide concentrations and relative humidity. Under conditions of low CO2 concentration and low relative humidity (less than 25%), the aerosol was predominantly lithium monoxide with some lithium hydroxide and about 12% lithium carbonate. Under conditions of high relative humidity (greater than 75%), the aerosol was primarily lithium hydroxide with about 23% lithium carbonate. Although these two aerosols might be expected to have different acute toxicities based on their differing alkalinities, the 14-day LC50 values (with 95% confidence limits) determined after 4-hr exposures were 940 (730-1200) mg/m3 for the lithium oxide and hydroxide mixture and 960 (830-1200) mg/m3 for the lithium hydroxide aerosols. Histopathologic lesions were observed in the nasal turbinates, larynx, and occasionally in the lungs with both aerosols. The most prominent lesions were necrotizing laryngitis and ulcerative rhinitis. Pulmonary lesions represented a secondary extension of the upper respiratory tract lesions rather than a primary manifestation of lithium toxicity. The similarities in the LC50 values and also in the histopathologic lesions observed suggest that any Li2O in the aerosol reacted rapidly with water vapor in the respiratory tract to form LiOH prior to deposition.

Aerosols↗
PubMed2005

Aerosolized liposome-based delivery of amphotericin B to alveolar macrophages.

The present study was aimed at preparation, characterization, and performance evaluation of amphotericin B (Amp B)-loaded aerosolized liposomes for their selective presentation to lungs (alveolar macrophages), that being the densest site of Aspergillosis infection. Egg phosphatidylcholine (PC)- and cholesterol (Chol)-based liposomes were modified by coating them with alveolar macrophage-specific ligands (O-palmitoyl mannan, OPM, and O-polmitoyl pullulan, OPP). The prepared formulations were characterized in vitro for vesicle morphology, mean vesicle size, vesicle size distribution and percent drug entrapment. Pressurized packed systems based on preformed liposomal formulations in chlorofluorocarbon aerosol propellants were prepared. In vitro airways penetration efficiency of the liposomal aerosols was determined by percent dose reaching the peripheral airways, it was recorded 1.4-1.6 times lower as compared to plain drug solution-based aerosol. In vivo tissue distribution studies on albino rats suggested the preferential accumulation of OPM- and OPP-coated formulations in the lung macrophages. Higher lung drug concentration was recorded in case of ligand-anchored liposomal aerosols as compared to plain drug solution and plain liposome-based aerosols. The drug was estimated in the lung in high concentration even after 24 h. The drug-localization index calculated after 6 h was nearly 1.42-, 4.47-, and 4.16-fold, respectively, for plain, OPM-, and OPP-coated liposomal aerosols as compared to plain drug solution-based aerosols. These results suggest that the ligand anchored liposomal aerosols are not only effective in rapid attainment of high-drug concentration in lungs with high population of alveolar macrophages but also maintain the same over prolonged period of time. The significance of targeting potential of the developed systems was established.

Aerosols↗
PubMed2001

A study of workers' exposures to the inhalable and 'total' aerosol fractions in the primary nickel production industry using mannequins to simulate personal sampling.

This paper describes a study that was carried out at work sites in the primary nickel production industry to investigate the difference between inhalable and 'total' aerosol exposures by using the mannequin sampling method, and to compare the results with those from an earlier study where actual workers' personal exposures were assessed in the same way. Experiments were carried out at 21 work sites located in mining, milling, smelting, and refining works of two primary nickel production companies. During sampling, mannequins were used to simulate the physical presence of workers and the 'exposures' of these were obtained for strategic positions at selected work sites. The orientations of each mannequin with respect to the wind were rotated through 90 degrees every hour in order to simulate the approximate orientation-averaging corresponding to actual workers. Two samplers were placed side-by-side on each mannequin: the Institute of Occupational Medicine (IOM) inhalable aerosol sampler, and the 37-mm plastic cassette widely used as a personal sampler for 'total' aerosol. Each collected sample was analyzed to obtain both overall dust and overall nickel content. A total of 116 such sample pairs were collected. The results show that inhalable aerosol exposure levels-for both overall dust and for total nickel content-were consistently and significantly higher than the corresponding total aerosol exposure levels. Weighted least squares linear regression yielded (inhalable/'total') aerosol ratios ranging from 1.38 to 3.90 and 1.20 to 4.01, respectively, for overall dust and for total nickel content for different work sites. Comparison of these results with those from the earlier study of actual workers' personal exposures were in good agreement for most of the work sites studies. However, the actual intensities of exposure using the mannequin sampling method were consistently lower than those obtained from actual workers' personal sampling in our earlier study. The consistency of the (inhalable/'total') ratios between mannequin and actual personal sampling strongly suggests that the characteristics of the aerosol sampled by the two methods, most notably the particle size distribution, were the same. This in turn suggests that mannequin sampling can be useful in occupational hygiene for determining such properties of personal workers' exposures. It certainly provides a useful and cost effective method for determining factors at work sites in individual industry settings by which to examine the impact of changing exposure assessment from one based on 'total' aerosol to the recommended new approach based on inhalable aerosol.

Aerosols↗
PubMed2000

Characterisation and source identification of PM10 aerosol samples collected with a high volume cascade impactor in Brisbane (Australia).

PM10 (particulate matter with aerodynamic diameter < 10 microm) samples of Brisbane air were collected and fractionated into six size fractions (< 0.5, 0.5-0.61, 0.61-1.3, 1.3-2.7, 2.7-4.9 and 4.9-10 microm) with a high volume cascade impactor. The chemical composition of the samples was analysed by techniques including Ion Beam Analysis. On average, 42% of the aerosol mass is in the > 2.7-microm size fraction, with the < 0.5-microm size fraction also contributes 41% of the aerosol mass. The composition of the < 1.3-microm aerosols is significantly different to that of the > 1.3-microm aerosols. The aerosol mass and concentrations of chemical components related to human activities show a bimodal size-distribution pattern, with most of the mass in the accumulation range (< 0.65 microm). The size geometric mean of aerosol mass is 0.96 microm in the samples collected from an industrial/residential site, and is 1.74 microm in the samples collected from a suburban site. The size geometric mean of concentrations of chemical components related to human activities ranges from 0.16 to 0.57 microm. The concentrations of crustal matter and sea salt show a unimodal size-distribution pattern, and with geometric means of 3.73 and 4.12 microm, respectively. Four source factors were resolved by multivariate analysis techniques for the size-fractionated aerosol samples, namely the soil, sea salt, organics and vehicular exhausts factors. The source fingerprints of the factors vary in the size ranges and have implications on the formation and dispersal processes of the particles. On average, the soil and sea salt factors contribute more than 80% of the aerosol mass in the > 2.7-microm fractions, while the organics and vehicular exhausts factors explain almost all the aerosol mass in the < 0.61-microm fractions.

Aerosols↗
PubMed2001

Source regions for atmospheric aerosol measured at Barrow, Alaska.

Aerosol data consisting of condensation nuclei (CN) counts, black carbon (BC) mass concentration, and aerosol light scattering coefficient at the wavelength of 450 nm (SC) measured at Barrow, AK, from 1986 to 1997 have been analyzed. BC and SC show an annual cycle with the Arctic haze maxima in the winter and spring and the minima in the summer. The CN time series shows two maxima in March and August. Potential source contribution function (PSCF) that combines the aerosol data with air parcel backward trajectories was applied to identify potential source areas and the preferred pathways that give rise to the observed high aerosol concentrations at Barrow. Ten-day isentropic back trajectories arriving twice daily at 500 and 1500 m above sea level were calculated for the period from 1986 to 1997. The PSCF analyses were performed based on the 80th percentile criterion values for the 2- and 24-h averages of the measured aerosol parameters. There was a good correspondence between PSCF maps for the 2- and 24-h averages, indicating that 1-day aerosol sampling in the Arctic adequately represents the aerosol source areas. In winter, the high PSCF values for BC and SC are related to industrial source areas in Eurasia. The trajectory domain in winter and spring is larger than in summer, reflecting weaker transport in summer. No high PSCF areas for BC and SC can be observed in summer. The result is related to the poor transport into the Arctic plus the strong removal of aerosol by precipitation in summer. In contrast to the BC and SC maps, the CN plot for summer shows high PSCF areas in the North Pacific Ocean. High CN values appearto be mostly connected with the long-range transport from Eurasia in winter and spring and with the reduced sulfur compound emission from biogenic activities in the ocean in the summer. PSCF analysis was found to be effective in identifying potential aerosol source areas.

Aerosols↗
PubMed2004

Simulating organic aerosol formation during the photooxidation of toluene/NOx mixtures: comparing the equilibrium and kinetic assumption.

Organic compounds contribute an appreciable mass to particulate matter and thus impact the hygroscopic and radiative properties of an aerosol distribution. Being able to predict the chemical and physical properties of aerosols based on their size and composition is critical to assessing their impact on air quality, visibility, and climate change. In this study, a comparison was performed between an equilibrium and a kinetic model for simulating organic aerosol formation during the photooxidation of toluene/NO/isopropyl nitrite mixtures. Both models used an explicit gas-phase toluene scheme (University of Leeds Master Chemical Mechanism version 3.0) and provided a prediction of individual products partitioned to the aerosol phase. After incorporating a heterogeneous wall reaction scheme regenerating NOx from HNO3 and HNO2, the gas-phase scheme was able to simulate the observed toluene decay within 5% and NO decay within 30% for all of the chamber experiments. The models reproduced the general magnitude of the aerosol yields but suggest a weaker trend dependence on aerosol mass loading. A few nonvolatile compounds were predicted to compose the majority of the aerosol-phase mass with multifunctional organic nitrates being the dominant organic aerosol functional group. The hygroscopic diameter growth factor for the organic phase was predicted to be 1.1 at a relative humidity of 79%. We conclude with a list of recommended laboratory experiments to help constrain and validate aerosol process models.

Aerosols↗
PubMed2004

Measurement of contemporary and fossil carbon contents of PM2.5 aerosols: results from Turtleback Dome, Yosemite National Park.

The impact of aerosol particulate matter of mean mass aerodynamic diameter < or = 2.5 microm (PM2.5 aerosols) on health, visibility, and compliance with the U.S. EPA's regional haze regulations is a growing concern. Techniques that can help better characterize particulate matter are required to better understand the constituents, causes, and sources of PM2.5 aerosols. Measurement of the 14C/C ratio of the PM2.5 aerosols, the absence of 14C in fossil carbon materials, and the known 14C/C levels in contemporary carbon materials allow the use of a two-component model to derive contemporary and fossil carbon contents of the particulate matter. Such data can be used to estimate the relative contributions of fossil fuels and biogenic aerosols to the total aerosol loading. Here, the methodology for performing such an assessment using total suspended particulate hi-vol aerosol samplers to collect PM2.5 aerosols on quartz fiber filters and the technique of accelerator mass spectrometry to measure 14C/C ratios is presented and illustrated using PM2.5 aerosols collected at Yosemite National Park.

Aerosols↗
PubMed2005

Sterols and anionic surfactants in urban aerosol: emissions from wastewater treatment plants in relation to background concentrations.

Aerosol particles that are emitted from aeration tanks of wastewater treatment plants (WWTPs) can be enriched with environmentally relevant wastewater constituents. In this study, aerosol particles were sampled simultaneously at the pre-aeration tank of a municipal WWTP and at two urban locations approximately 1 km away from the WWTP to evaluate the significance of these aerosol emissions. Moreover, aerosol particles were sampled at a small wastewater irrigation facility and at a rural site. In aerosol particles and wastewater, six sterols (cholesterol, coprostanol, campesterol, beta-sitosterol, stigmasterol, stigmastanol) and anionic surfactants (expressed in terms of methylene blue active substances, MBAS) were quantified. The results showed significantly higher concentrations of sterols and MBAS at the WWTP than atthe urban locations. At the WWTP, average concentrations of cholesterol (848 +/- 321 pg m(-3)), coprostanol (1132 +/- 565 pg m(-3)), and MBAS (132 +/- 43 ng m(-3)) in aerosol were approximately twice as high. This can be attributed to emissions from the treatment tank. Coprostanol, a unique tracer for wastewater, was detected only occasionally at the urban locations. The results of this study show that the aeration of wastewater is a continuously operating local source for organic compounds in aerosol. The wastewater irrigation facility was a minor source of aerosol-bound sterols (coprostanol, 287 +/- 218 pg m(-3)) and anionic surfactants (64 +/- 32 ng m(-3)). Except for coprostanol, all compounds were also present in samples of rural aerosol.

Aerosols↗
PubMed2001

Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols.

Aerosols affect the Earth's temperature and climate by altering the radiative properties of the atmosphere. A large positive component of this radiative forcing from aerosols is due to black carbon--soot--that is released from the burning of fossil fuel and biomass, and, to a lesser extent, natural fires, but the exact forcing is affected by how black carbon is mixed with other aerosol constituents. From studies of aerosol radiative forcing, it is known that black carbon can exist in one of several possible mixing states; distinct from other aerosol particles (externally mixed) or incorporated within them (internally mixed), or a black-carbon core could be surrounded by a well mixed shell. But so far it has been assumed that aerosols exist predominantly as an external mixture. Here I simulate the evolution of the chemical composition of aerosols, finding that the mixing state and direct forcing of the black-carbon component approach those of an internal mixture, largely due to coagulation and growth of aerosol particles. This finding implies a higher positive forcing from black carbon than previously thought, suggesting that the warming effect from black carbon may nearly balance the net cooling effect of other anthropogenic aerosol constituents. The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH4, suggesting that black carbon may be the second most important component of global warming after CO2 in terms of direct forcing.

Aerosols↗
PubMed2002

A satellite view of aerosols in the climate system.

Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrialization and an expanding population, may adversely affect the Earth's climate and water supply.

Aerosols↗
PubMed2005

Global estimate of aerosol direct radiative forcing from satellite measurements.

Atmospheric aerosols cause scattering and absorption of incoming solar radiation. Additional anthropogenic aerosols released into the atmosphere thus exert a direct radiative forcing on the climate system. The degree of present-day aerosol forcing is estimated from global models that incorporate a representation of the aerosol cycles. Although the models are compared and validated against observations, these estimates remain uncertain. Previous satellite measurements of the direct effect of aerosols contained limited information about aerosol type, and were confined to oceans only. Here we use state-of-the-art satellite-based measurements of aerosols and surface wind speed to estimate the clear-sky direct radiative forcing for 2002, incorporating measurements over land and ocean. We use a Monte Carlo approach to account for uncertainties in aerosol measurements and in the algorithm used. Probability density functions obtained for the direct radiative forcing at the top of the atmosphere give a clear-sky, global, annual average of -1.9 W m(-2) with standard deviation, +/- 0.3 W m(-2). These results suggest that present-day direct radiative forcing is stronger than present model estimates, implying future atmospheric warming greater than is presently predicted, as aerosol emissions continue to decline.

Aerosols↗
PubMed1994

Direct-reading instruments for aerosols. A review.

Direct-reading instruments for aerosols have not had the popularity within the industrial hygiene community that similar instruments for gases and vapours have enjoyed. There are several reasons for this: aerosols have complex properties that are difficult to characterize with a single measurement, commercial instruments often do not provide an accurate measure of a useful aerosol property and aerosol instruments are relatively expensive for industrial hygiene use. A variety of instruments are commercially available and are briefly reviewed. Two general classes of instruments used for industrial hygiene measurements are covered: field instruments and research instruments. The International Symposium on Air Sampling Instrument Performance held in Research Triangle Park, NC, USA, in October, 1991 included a workshop on direct-reading aerosol instruments that produced several recommendations to advance the state of the art. The two primary recommendations approved by the symposium attendees were to develop voluntary consensus standards for aerosol mass measuring instruments and optical particle counters and to develop an accurate, portable, direct-reading aerosol mass monitor. Some progress is being made on the latter recommendation through a project supported by the US Bureau of Mines. Other instruments have found specific application in industrial hygiene measurements. A miniaturized condensation nucleus counter is being used to estimate fit factors for respirators. A fibre monitor is used for monitoring asbestos, especially in asbestos abatement operations. Optical particle counters are used for low-concentration aerosols, especially in clean rooms. Aerosol research instruments are being used to evaluate and improve field instrumentation, such as respirable, thoracic and inhalable samplers and cascade impactors.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed2000

Aerosol light scattering measurements as a function of relative humidity.

The hygroscopic nature of atmospheric fine aerosol was investigated at a rural site in the Great Smoky Mountains National Park during July and August 1995. Passing the sample aerosol through an inlet, which housed an array of Perma Pure diffusion dryers, controlled the sample aerosol's relative humidity (RH). After conditioning the aerosol sample in the inlet, the light scattering coefficient and the aerosol size distribution were simultaneously measured. During this study, the conditioned aerosol's humidity ranged between 5% < RH < 95%. Aerosol response curves were produced using the ratio bspw/bspd; where bspw is the scattering coefficient measured at some RH greater than 20% and bspd is the scattering coefficient of the "dry" aerosol. For this work, any sample RH values below 15% were considered dry. Results of this investigation showed that the light scattering ratio increased continuously and smoothly over the entire range of relative humidity. The magnitude of the ratio at a particular RH value, however, varied considerably in time, particularly for RH values greater than approximately 60%. Curves of the scattering coefficient ratios as a function of RH were generated for each day and compared to the average 12-hour chemical composition of the aerosol. This comparison showed that for any particular RH value the ratio was highest during time periods of high sulfate concentrations and lowest during time periods of high soil or high organic carbon concentrations.

Aerosols↗
PubMed1986

Characterization of particleboard aerosol--size distribution and formaldehyde content.

Health hazards unique to particleboard include the generation of urea-formaldehyde resin bound in wood aerosol and release of formaldehyde gas that can be inhaled by the worker. A particleboard aerosol was generated by a sanding process and collected under laboratory conditions that determined the particle size distribution and formaldehyde content. Three side-by-side Marple 296 personal cascade impactors with midget impingers attached downstream collected particleboard aerosol and gaseous formaldehyde for ten sample runs. Gravimetric analysis quantified the collected aerosol mass, and chromotropic acid/spectrophotometric analytical methods were employed for formaldehyde content in particleboard aerosol and gaseous formaldehyde liberated from sanded particleboard. Significant variations (p less than .005) were observed for the particleboard mass and gaseous formaldehyde collected between sample runs. No significant differences (alpha = .05) were observed for the aerosol size distribution determined and formaldehyde content in particleboard aerosol per unit mass for sampling trials. The overall MMAD of particleboard aerosol was 8.26 microns AED with a sigma g of 2.01. A predictive model was derived for determining the expected formaldehyde content (microgram) by particleboard aerosol mass (mg) collected and particulate size (micron AED).

Aerosols↗
PubMed1998

Method for measuring the spatial variability of aerosol penetration through respirator filters.

Fibrous filter media are widely used in respirators to remove airborne particulate matter from the inhaled airflow of workers. The N95 half-mask particulate respirator appears to be the most frequently used respirator under the new NIOSH regulation, 42 CFR 84. Considerable spatial variability in light penetration through the fibrous filter medium of an N95 respirator can be seen by visual observation when it is held to the light. This variability is due to the way in which the fibers are manufactured and laid down to form the filter medium. Similar spatial variability is expected in the aerosol penetration through the filters. Therefore, a test method has been developed for measuring the spatial variability in aerosol penetration. The main components of this method are an aerosol generator, a filter test stand with a movable sampling inlet, an aerosol size spectrometer, and an aerosol photometer. Measurements with the filter media of N95 respirators, tested at average filtration velocities corresponding to light, moderate, and heavy work loads, have shown spatial variations in aerosol penetration in excess of 100% relative to the average aerosol penetration for the entire respirator. N95 respirators are required to be at least 95% efficient (i.e., less than 5% penetrating) at the most penetrating particle size, when tested at 85 L/min. Tests with the new method have shown that the aerosol penetration of the most penetrating particles of about 0.1 micron diameter may locally be higher than 5%, while the average aerosol penetration of 0.1 micron particles is less than 5%.

Aerosols↗