Cascade impactor, particle sizing using

The data upon which these curves are based were obtained by use of a cascade impactor, which sizes particles according to their aerodynamic characteristics. The aerodynamic diameter of a particle is the diameter of a spherical particle of unit density which, when falling, reaches the same terminal velocity as the particle in question. This will be discussed further below. 

Cascade impactors have been used to collect e.g. perfluorinated octane sulfonate (PFOS) and perfluorinated octanoic carboxyhc acid (PFOA) on particles by particle size distribution (Harada et al. 2006). 

Cascade impactors. Cascade impactors provide information on particle or droplet size spectra within airborne sprays. The air is drawn through a series of chambers that allow sequential separation of different particle sizes based on their different velocities and masses. This type of collector is not as widely used as the sampling devices discussed previously because they are relatively difficult to operate and are expensive. Further information on this and other types of sampler for spray research can be found in the literature. ... 

It must also be emphasized that the major mass of a heterodispersed aerosol may be contained in a few relatively large particles, since the mass of a particle is proportional to the cube of its diameter. Therefore, the particle-size distribution and the concentration of the drug particles in the exposure atmosphere should be sampled using a cascade impactor or membrane filter sampling technique, monitored using an optical or laser particle-size analyzer, and analyzed using optical or electron microscopy techniques. 

The size distribution of the particulate matter in the 0.01-5 ym size range is analyzed on line using an electrical mobility analyzer and an optical particle counter. Samples of particles having aerodynamic diameters between 0.05 and 4 ym are classified according to size using the Caltech low pressure cascade impactor. A number of analytical procedures have been used to determine the composition distribution in these particles. A discrete mode of particles is observed between 0.03 and 0.1 ym. The major components of these particles are volatile elements and soot. The composition of the fine particles varies substantially with combustor operating conditions. 

The aerosol produced by a laboratory pulverized coal combustor was size classified in the range 0.03 to 4 ym Stokes equivalent diameter using a low-pressure cascade impactor. The samples thus collected were analyzed using a focussed beam particle induced X-ray emission technique. This combination of techniques was shown to be capable of resolving much of the structure of the submicron coal ash aerosol. Two distinct modes in the mass distribution were observed. The break between these modes was at a particle size of about 0.1... 

Particle Number Concentration and Size Distribution. The development of aerosol science to its present state has been directly tied to the available instrumentation. The introduction of the Aitken condensation nuclei counter in the late 1800s marks the beginning of aerosol science by the ability to measure number concentrations (4). Theoretical descriptions of the change in the number concentration by coagulation quickly followed. Particle size distribution measurements became possible when the cascade impactor was developed, and its development allowed the validation of predictions that could not previously be tested. The cascade impactor was originally introduced by May (5, 6), and a wide variety of impactors have since been used. Operated at atmospheric pressure and with jets fabricated by conventional machining, most impactors can only classify particles larger... 

Chemical Composition Aerosol composition measurements have most frequently been made with little or no size resolution, most often by analysis of filter samples of the aggregate aerosol. Sample fractionation into coarse and fine fractions is achieved with a variety of dichotomous samplers. These instruments spread the collected sample over a relatively large area on a filter that can be analyzed directly or after extraction Time resolution is determined by the sample flow rate and the detection limits of the analytical techniques, but sampling times less than 1 h are rarely used even when the analytical techniques would permit them. These longer times are the result of experiment design rather than feasibility. Measurements of the distribution of chemical composition with respect to particle size have, until recently, been limited to particles larger than a few tenths of a micrometer in diameter and relatively low time resolution. One of the primary tools for composition-size distribution measurements is the cascade impactor. 

The fact that fine atmospheric particles are enriched in a number of toxic trace species has been known since the early 1970s. Natusch and Wallace (20, 21) observed that the fine particles emitted by a variety of high-temperature combustion sources follow similar trends of enrichment with decreasing particle size as observed in the atmosphere, and they hypothesized that volatilization and condensation of the trace species was responsible for much of the enrichment. Subsequent studies of a number of high-temperature sources and fundamental studies of fine-particle formation in high-temperature systems have substantiated their conclusions. The principal instruments used in those studies were cascade impactors, which fractionate aerosol samples according to the aerodynamic size of the particles. A variety... 

JET IMPACTION. A rapidly moving particle, striking a suitably coated surface, will leave an impression whose size is a function of the original drop diameter. Pilcher (7S) illustrates the operation of the jet impactor. The higher the jet velocity, the smaller the particle size which will impinge. An instrument called the cascade impactor consists of a series of these slides. The jet velocity is increased from slide to slide thus, the cascade is useful in determining droplet size distributions. 

Suspensions contain micronized drug for proper delivery to and absorption in the respiratory system. Typical particle size of the micronized drug is from 2 to 5 microns [5], Aerodynamic mean particle size as measured by cascade impactor or direct method of microscopic analysis is usually from 0.5 to 4 microns [5], Additional particle-sizing techniques such as light scattering can be used [6],... 

Particle Size Analysis Many particle-size-analysis methods suitable for dry-dust measurement are unsuitable for liquids because of coalescence and drainage after collection. Measurement of particle sizes in the flowing aerosol stream by using a cascade impactor is one... 

Cascade impactors and cyclones have been used in order to determine the aerodynamic size distribution. Impactors allow the classification of particles with an aerodynamic diameter Dp between 0.1 pm < Dp < 5 pm, while cyclones work in the 2 to 20 pm range. 

Cascade Impactor Characteristics. If the cascade impactor is to be used to obtain information on the diameters of particles in the atmosphere, then the distribution of the particle sizes on each stage must be known. Two approaches were used to obtain these data. The first used an empirical equation derived for this impactor (26,27,28) ... 

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