Aerosol containers distribution

An example of the wealth of information contained in state-of-the-art measurements of aerosol size distributions is shown in Figure 8. Here the distribution of number concentration is shown as a function of particle size versus time of day over a 16 h period. A nucleation event starting at 8 a.m. is indicated by the abrupt increase in concentration of the smallest particles, which are about 3 nm in diameter and at the limit of... 

Laser Doppler velocimetry has been combined with acoustic excitation to allow the derivation of the relaxation time for particles, from which the aerodynamic diameter can be calculated [132-136], The particle relaxation time is derived from the velocity amplitude of the aerosol particle and that of the medium while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure the velocity amplitude of the particle, and a microphone is used to measure the velocity amplitude of the medium. The aerodynamic diameter of the particle can be derived from the relaxation time and the known particle density. The method can be applied to real-time in situ measurement of the size distribution of an aerosol containing both solid and liquid droplets in the diameter range of 0.1 -10 pm. 

The growth law for a polydisperse aerosol can be determined by measuring the change in the size distribution function with lime. In experiments by Heksler and Friedlander (1977), small quantities of organic vapors that served as aerosol precursors were added to a sample of the normal atmospheric aerosol contained in an 80-m bag exposed to solar radiation. The bag was made of a polymer film almost transparent to. solar radiation in the UV range and relatively unreactive with ozone and other species. Chemical reaction led to the formation... 

The clouds observed in the lower troposphere when the inflow of arctic air (BT IV) dominates in the region are on average characterized by the same values of the optical parameters as the clouds in the previously reviewed case. However, the spectra of the distribution of the aerosol surface area versus particle size are noticeably shifted to the range of smaller particles (radiuses r=0.1-0.2 //m), and are described by a broader logarithmically normal function (curves 3 and 4). The observation can be explained by the offset of aerosol containing a great amount of loes dust and products of anthropogenic pollution composed of outbursts from the industrial plants of Kazakhstan. 

After inertial separation of the particles within these instruments, it is necessary to quantify the amount of drug in each of the size fractions in order to derive an aerosol size distribution. This is usually performed by chemical assay for drug substance and may entail a variety of analytical techniques. However, it is important that drug substance be assayed, because most pharmaceutical aerosols contain excipients and the distribution of the drug and excipients will not necessarily be uniform and in equal proportion aaoss the entire size distribution. 

In this chapter, size classification refers to the separation of particles by size so that the resulting aerosol contains particles of a given size, whereas size characterization is the determination of the size distribution of the aerosol. Size characterization of nanoflbers and nanotubes is commonly performed by transmission electron microscopy (TEM). TEM analysis has proven invaluable for examining the structure and composition of individual particles and is also valuable for size characterization if immediate feedback is not needed. Inasmuch as the particles must first be collected and then analyzed, the process is slow and laborious. 

Fig. 6. Size distribution of an urban aerosol showing the three modes containing much of the aerosol mass. The fine mode contains particles produced by condensation of low volatility gases. The mid-range, or accumulation mode, results from coagulation of smaller aerosols and condensation of gases on preexisting particles. Coarse particulates, the largest aerosols, are usually generated mechanically.

Denmark 1.5 days after the explosion. Air samples collected at Roskilde, Denmark on April 27-28, contained a mean air concentration of 241Am of 5.2 pBq/m3 (0.14 fCi/m3). In May 1986, the mean concentration was 11 pBq/m3 (0.30 fCi/m3) (Aarkrog 1988). Whereas debris from nuclear weapons testing is injected into the stratosphere, debris from Chernobyl was injected into the troposphere. As the mean residence time in the troposphere is 20-40 days, it would appear that the fallout would have decreased to very low levels by the end of 1986. However, from the levels of other radioactive elements, this was not the case. Sequential extraction studies were performed on aerosols collected in Lithuania after dust storms in September 1992 carried radioactive aerosols to the region from contaminated areas of the Ukraine and Belarus. The fraction distribution of241 Am in the aerosol samples was approximately (fraction, percent) organically-bound, 18% oxide-bound, 10% acid-soluble, 36% and residual, 32% (Lujaniene et al. 1999). Very little americium was found in the more readily extractable exchangeable and water soluble and specifically adsorbed fractions. 

Table I presents the average aerodynamic distributions of Pb-212 and Pb-214, as well as the frequency with which Pb-214 or Pb-212 was the dominant isotope in each size range. The Aitken nuclei fraction (below 0.08 pm) contained a higher percentage of Pb-212 activity compared with Pb-214 in 69.6% of the measurements. The predominance of Pb-212 in this fraction is also illustrated by the distributions reported in Figure 1. In the remaining measurements, where Pb-214 was fractionally more abundant below 0.08 um, the disparity between the relative amounts of each isotope was not nearly as dramatic. Conversely, Figure 1 and Table I illustrate that Pb-214 is generally enriched in the accumulation mode aerosol, particularly between 0.11 and 0.52 ]xm, where most of the surface area and mass occurs.

Program faculty members are developing an automated cascade impactor for collection of task-based size distribution data of beryllium-containing aerosols. Based on the size distribution, the fraction of beryllium-containing aerosol penetrating a respirator and the inhalation and deposition in different regions of the lungs can be estimated. 

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 AERx pulmonary delivery system [40,41] can be regarded as a combination of a MDI and a nebulizer. This system forms an aerosol by extrusion of an aqueous drug-containing solution through a disposable nozzle containing an array of precisely micromachined holes. The droplets are entrained by the airflow passing over the blister. Control over the size distribution of the holes enables the formation of droplets having a narrow size distribution. 

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