Aerosol aerodynamic size

OG Raabe. Aerosol aerodynamic size conventions for inertial sampler calibration. J Air Pollution Control Assoc 26 856-860, 1976. 

Raabe, O.G. (1979). Design and use of the Mercer-style impactor for characterization of aerosol aerodynamic size distributions. In Aerosol MeasuremerU. University Presses of Florida, Gainesville, FL, pp. 135-140. 

The principle of inertial impaction is employed to sample aerosols aerodynamically for characterization of particle size and will be dealt with theoretically later in this chapter. 

Aerodynamic Size Associations of Natural Radioactivity with Ambient Aerosols... 

Aerodynamic Size Distributions of Naturally-Radioactive Aerosols. Measurements of radionuclide distributions using cascade impactors indicate that Be-7 and Pb-210 are associated with larger aerosols than Pb-212 and Pb-214 (Robig et al., 1980 Papastefanou and Bondietti, 1986). Measurements of Pb-210 associations over oceans indicated activity median aerodynamic diameters (AMAD) near 0.6 pm (Sanak et al., 1981). The impactor measurements of Moore et al. (1980) on Pb-210, Bi-210, and Sr-90 sizes in continental air indicated that about 80% of the activity from all three nuclides was associated with aerosols below 0.3 pm. That work also determined that the mean age of aerosol Pb-210 was about a week. Knuth et al. (1983) compared Pb-210 and stable Pb sizes at a continental location and found that 78% of the Pb-210 found below 1.73 pm was smaller than 0.58 pm. Young (1974) reported that the most of the Be-7 in the atmosphere was associated with submicron aerosols. 

This paper summarizes part of the results of an investigation designed to characterize the aerodynamic size distributions of natural radioactivity and to evaluate the results in the context of sulfate distributions and recent advances in the understanding of aerosol growth mechanisms. This paper, while emphasizing our results on Pb-212 and Pb-214, also summarizes our initial data for longer-lived radionuclides. 

Measurements on aerodynamic sizes of atmospheric aerosols and associated radionuclides were carried out with Anderson 2000, Inc., 1-ACFM Ambient Impactors with or without the Anderson low-pressure modification, as well as with Sierra model 236 (six-stage) high-volume impactors (HVI). The 1-ACFM design operated at 28... 

Pb-212 and S0% Distributions. The aerodynamic size distributions of Pb-212 and S0 were quite different, reflecting the different dependencies of surface area and volume on aerosol diameter (Friedlander, 19/7). Pb-212, like the other... 

The aerodynamic size distributions of Pb-214, Pb-212, Pb-210, Be-7, P-32, S-35-SoJ , and stable SO4 were measured using cascade impactors. Pb-212 and Pb-214, measured by alpha spectroscopy, were largely associated with aerosols small than 0.52 11m. Based on over 46 low-pressure impactor measurements, the mean activity median aerodynamic diameter (AMAD) of Pb-212 was found to be 0.13 11m, while for Pb-214 the AMAD was larger—0.16 lim. The slightly larger size of Pb-214, confirmed with operationally different impactors, was attributed to a-recoil-driven redistribution of Pb-214 following decay of aerosol-associated Po-218. A recoil model was presented that explained this redistribution. Low-pressure impactor measurements indicated that the mass median aerodynamic diameter of SoJ ... 

Papastefanou, C. and E. A. Bondietti, Aerodynamic Size Associations of Pb-212 and Pb-214 in Ambient Aerosols, submitted to Health Phys. (1986). 

Solomon, P. A., J. L. Moyers, and R. A. Fletcher, High-Volume Dichotomous Virtual Impactor for the Fractionation and Collection of Particles According to Aerodynamic Size, Aerosol Sci. Technol., 2, 455-464 (1983). 

A related technique that is suitable for measurement of aerosols at lower mass loadings is the aerodynamic particle sizer (3, 10). In this instrument the aerosol is rapidly accelerated through a small nozzle. Because of their inertia, particles of different aerodynamic sizes are accelerated to different velocities, and the smallest particles reach the highest speeds. The particle velocity is measured at the outlet of the nozzle. From the measurements of velocities of individual particles, particle size distributions can be determined. The instrument provides excellent size resolution for particles larger than about 0.8 xm in diameter, although sampling difficulties limit its usefulness above 10 xm. 

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... 

In general, particles or droplets in the size range 5-10 wm tend to deposit in the nasal passages. Although the extent and site of particle deposition can be estimated from a knowledge of the aerodynamic size distribution of the aerosol, the situation can be complicated by the fact that the size of the particle can increase (and possibly its density decrease) as a result of water condensation, due to the humidity change upon entering the nasal cavity. 

The mass median aerodynamic diameter (MMAD) is defined as the aerodynamic diameter which divides the aerosol mass size distribution in half. 

The MDI may provide up to several hundred actuations, each containing typically from about 10 to 500 pg of drug dispersed in a 25 to 100 pi metered volume of liquid. The discharged liquid undergoes flash evaporation of the propellant to produce a finely dispersed aerosol spray. The deposition, and hence the clinical efficacy, are critically dependent on the mass of inhaled particles, which must have an appropriate aerodynamic size, typically less than 5 pm, to be deposited in the lungs (the respirable fraction). ... 

Fig. 7 A Doppler-shift procedure for measuring the aerodynamic size of aerosol fine particles is used by the TSI aerosol particle sizer. (From...

Pulmonary delivery of insulin for systemic absorption in the treatment of diabetes has been studied extensively since the early days of insulin discovery almost a century ago. Colthorpe et al. and Pillai et al. demonstrated in rabbit and monkey models, respectively, that the deeper into limg the dose of insulin was delivered, the higher was the bioavailability. The work of Laube, Benedict, and Dobs showed the need to achieve deep pulmonary deposition of this molecule for efficient absorption in humans. Handheld liquid and dry powder delivery systems have been developed to generate insulin-containing aerosols with the majority of the particles in the aerodynamic size range 1-3 pm. The relative bioavailability compared with subcutaneous injection based on the insulin contained in the dosage form was 110/ [52] powder system and for the aqueous-based... 

The aerodynamic size distribution is a key parameter affecting the regional distribution, and hence the absorption, of macromolecular drugs from the lung. The synchronization of optimum breathing and aerosol delivery appears to be a prerequisite for efficient and reproducible delivery the key parameters to control are listed in Table 1. 

In addition, because the respirable fraction of the aerosol cloud that is emitted from a suspension MDI is highly dependent on the geometric size of the bulk drug particles (i.e., the aerodynamic size cannot be smaller than the initial geometric size of the primary particles), there are limitations to the respirable fraction that can be achieved. As such, solution formulations offer opportunities to circumvent some of these problems, particularly with drugs that have a significant solubility in the volatile propellants, where greater respirable fractions can be obtained [36]. 

As with most questions on particle size, the answer is very dependent on the definition used and the experimental technique. For a dynamic aerosol cloud, the correct definition is the aerodynamic particle size, which is the diameter of an equivalent sphere of unit density. An equivalent sphere is a conventional assumption in particle sizing, but for the aerodynamic size, the density is included to account for the momentum of the particle, i.e., both mass and velocity are important. The technique chosen for measurement must include these parameters, and impaction is the normally chosen technique, which also reflects the major deposition mechanism in the lung. A schematic of an impaction plate is given in Figure 10.3. 

In the applications of gas-solid flows, measurements of particle mass fluxes, particle concentrations, gas and particle velocities, and particle aerodynamic size distributions are of utmost interest. The local particle mass flux is typically determined using the isokinetic sampling method as the first principle. With the particle velocity determined, the isokinetic sampling can also be used to directly measure the concentrations of airborne particles. For flows with extremely tiny particles such as aerosols, the particle velocity can be approximated as the same as the flow velocity. Otherwise, the particle velocity needs to be measured independently due to the slip effect between phases. In most applications of gas-solid flows, particles are polydispersed. Determination of particle size distribution hence becomes important. One typical instrument for the measurement of particle aerodynamic size distribution of particles is cascade impactor or cascade sampler. In this chapter, basic principles, applications, design and operation considerations of isokinetic sampling and cascade impaction are introduced. 

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