Aerosol particle size

Thus some generalisations can be made as to the origins of aerosol particles based on their size (Fig. 7.1). Certain metals such as lead and cadmium tend to be associated with small particles as a result of their abundance in high-temperature combustion processes (smelting, incineration, fuel burning, etc.) and their 

The concentration of metals in atmospheric aerosols and rainwater (Table 7.1) is therefore a function of their sources. This includes both the occurrence of the metals in combustion processes and their volatility, as well as their occurrence in crustal dust and seawater. As a result of this, the size distribution of different metals is very different and depends on the balance of these sources. For a particular metal this distinction is similar in most global locations (Table 7.2), although some variability does occur as wind speed and distance from source exert an influence on the particle size distribution spectrum (Slinn, 1983). Once in the atmosphere particles can change size and composition to some extent by condensation of water vapour, by coagulation with other particles, by chemical reaction, or by activation (when supersaturated) to become cloud or fog droplets (Andreae et al., 1986 Arimoto et al., 1997 Seinfeld and Pandis, 1998). 

The relative importance of the different sources can be confirmed by considering enrichment factors (Ef)  

---

Several groups investigated the use of liposomes for the intra-pulmonary delivery. Farr et al. (1985) showed that the deposition of aerosolized liposomes in the human lung depends on the aerosol particle size. Short-term retention profiles for MLVs and SUVs deposited in the lung were indicative of clearance via the mucociliary transport mechanism. 

Lung deposition patterns and the relative contributions of the fecal and urinary pathways vary with the aerosol particle size. Evidence for this is provided by a study in which dogs inhaled Am02 aerosols having... 

WG Gorman, FA Carroll. Aerosol particle-size determination using laser holography. Pharm Technol 17 34-37, 1993. 

Busigin, A., A.W. van der Vooren and C.R. Phillips, A Technique for Calculation of Aerosol Particle Size Distributions from Indirect Measurements, J. Aeros. Sci. 11 359-366 (1980). 

FIGURE 9.23 (a) Aerosol particle size distribution measured at Pomona during the 1972 State of California Air Resources Board ACHEX program, (b) Calculated optical scattering by particles, bsp, for measured size distribution (adapted from Waggoner and Charl-son, 1976). 

Poll GP, Grim WM, Bacher FA, Yunker MH. Influence of formulation on aerosol particle size. J Pharma Sci 1969 58 484-486. 

A second factor in the deposition process is the physical size of the radioaerosol particles deposited during dry deposition. Particle size affects the efficiency of foliar collection of dry aerosol particles and may also be important in determining the rate of solution of soluble constituents within the aerosol particle. Lockhart et al. (7) indicated that nuclear debris in surface level air is generally associated with aerosol particle sizes about 0.5-1.0p in diameter. Martell (8) stated that high yield detonations causing condensation of "Sr at stratospheric altitudes leads to the formation of particles with diameters less than 1 fi. Hence,... 

Atmospheric aerosols are complex mixtures of particles derived from diverse sources. Soot from diesel engines, fly ash from coal combustion, and sulfates, nitrates, and organic compounds produced by atmospheric reactions of gaseous pollutants all contribute to the aerosol. Particle size and composition depend upon the conditions of aerosol formation and growth and determine the effects of atmospheric aerosols on human health, ecosystems, materials degradation, and visibility. Much of the research on environmental aerosols has focused on fine particles ranging from a few micrometers in... 

Fig. 7-4. Effect of aerosol particle size (d) on deposition velocity (Kg) to conifer and grass canopies (redrawn from Bonka and Horn, 1983).

Fig. 7-5. Effect of aerosol particle size on scavenging efficiency of raindrops, falling at an intensity of 1 mm h-1 (redrawn from Rbbig, 1979).

Smaller particles in the size range 0.5-5 pm may escape impaction in the upper airways and will deposit by impaction and sedimentation in the lower TB and A regions. If the aerosol particle size is between about 3 and 5 pm then deposition will predominantly occur in the TB region. If the particles are less than about 3 pm then appreciable deposition in the A region is likely to occur. 

During nebulization from airjet nebulizers, cooling of the reservoir solution occurs which, together with vapor loss, results in concentration of the dmg solution. This in turn produces an aerosol output in which the drag concentration increases with time. Concentration of the dmg solution in the reservoir can lead to drug recrystallization with subsequent blockage within the device or variation in aerosol particle size. 

Molecular clusters can be considered to be the smallest size range of an aerosol particle size distribution. Nucleation from the gas phase to particles or droplets involves, in the initial stages, the formation of clusters. Research on clusters provides a valuable approach to understanding, on a molecular level, the details of the transfer of molecules from the gaseous to the condensed state by either new particle formation or heterogeneous processes including adsorption onto or dissolution into particles. 

Acridine char nitrogen, retention as function of burnoff, 307/, 308/ Advection fluxes, calculation, 41-43 Aerosol particle size distribution, molecular clusters, 317 Aerosol scavenging pathway, acetic and formic acid formation, 223 Aerosol species, transformation over the western Atlantic, 52 Aerosol sulfate airborne determination, 298 See also Sulfate... 

Notice that for typical aerosol particle sizes, the exponential terms rapidly disappear. Note also that the particle is rapidly acquiring the velocity of the horizontal airflow. 

In the case of chemical pesticides, these include factors such as molecular weight and vapor pressure that determine the rate of evaporation into air of the pesticide in an applied material such as paint, or the release from aqueons solntion. In the case of biological agents, these include, for example, pathogenicity to hnmans, allergenicity, infectious dose levels and aerosol particle size distribntion. 

---