Aggregates aerosol

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. 

Deposition of the aggregated aerosol (0.5/mi) increased with increasing tidal volume (Wells etal., 1977). The lines in Fig. 7.10 represent results normalised to a tidal volume of 1.01. 

A comparison of the results with other data on the deposition of submicrometre aerosols, all related to a tidal volume of 11, is shown in Fig. 1.14. Although the density of the lead particles was greater than that of the other particles, the fractional deposition was similar, except possibly for the 0.5 pm size, because deposition was by Brownian motion. The percentage deposition increases for particles of diameter less than 0.1 /urn, and this means increased uptake of lead, relative to a given PbA, for persons exposed to non-aggregated aerosol, as found alongside major roads. 

Brasil, A.M., Farias, T.L. and Carvalho, M.G (2000). Evaluation of the Iractal properties of cluster-cluster aggregates. Aerosol Sci. TechnoL, 33, 440-454... 

Virtanen, A., Ristimaki, J. and Keskinen, J. (2004). Method for measuring effective density and fractal dimension of aerosol aggregates. Aerosol ScL Technol, 38,437-446. 

Fresh exhaust aerosols showed higher values of Vg than aged aggregated aerosols, and this was attributed to the higher diffusivity of the finer primary exhaust particles [3]. 

A comparative study of the spray-dried nanoparticulate budesonide versus micronized budesonide was performed Each powder was blended with lactose and then filled into a Clickhaler (ML Laboratories) DPL and the aerodynamic diameters of the dehvered powders were characterized on an Andersen eight-stage cascade impactor. The results, which are summarized grcq)hically in the following section, show that the MMAD of the nanoparticulate aggregate aerosol was much smaller than the MMAD of the micronized drug aerosol. A substantial fraction of... 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

For example, studies of the morphology of a number of flame-generated aggregates (different carbonaceous soots, A1203 aerosols, etc.) [203] by both TEM and ALS procedures resulted in D2 = 1.7 0.15, while analysis of silhouettes of computer models of seven proteins [211] gave a value of D2 = 1.120 0.025, etc. 

G. Firanescu, D. Hermsdorf, R. Ueberschaer, and R. Signorell, Large molecular aggregates From atmospheric aerosols to drug nanoparticles. Phys. Chem. Chem. Phys. 8, 4149 4165 (2006). 

Aerosolized MWNTs (32.61 mg/m3) Female Kunming mice Inhalation 8 days, 16 days, Most of the aggregations of MWNTs in the and 24 days alveoli were smaller than those in the bronchi. The aggregations induced proliferation and thickening of alveolar walls Li et al. (2007)... 

Spray pyrolysis routes have been extensively investigated to prepare Pt-based catalysts. Typically, a liquid feed of metal precursor and carbon is atomized into an aerosol and fed into a continuous furnace to evaporate and heat-treat to form a collectable powder. The method has good control over final aggregate particle size and metal particle size distributions, as well as producing powder without further isolation or separation. Hampton-Smith et al. have reviewed efforts of Superior MicroPowder (now Cabot Fuel Cells) in this area. ... 

Small amounts of surfactants may be used to prevent aggregation of proteins and may enhance the refolding process when the dried protein dissolves. Buffers may also help to prevent aggregation of the dissolved drug. Similarly, polymers may be used as aggregation inhibitors or to form matrices. Chan et al. [86] prepared crystalline powders of recombinant human deoxyribonuclease with high fractions of sodium chloride. These powders were formulated as adhesive mixtures on lactose and mannitol and showed improved aerosolization behaviour compared to the pure protein. 

Colloid chemistry investigates substance mixtures. These substance mixtures can be heterogenous, such as emulsions (in which tiny droplets of one liquid are dispersed in another), suspensions (consisting of a fine dispersion of solid particles in a liquid volume phase), and aerosols (in which liquid droplets are dispersed in the gas phase). However, there are also homogenous mixtures in which the solute is present in larger, supermolecular aggregates. These homogenous mixtures include micellar solutions and liquid crystalline... 

As mentioned in the preceding section, to stabilize a particle, metallic particles must be produced in an inert gas atmosphere and then trapped in appropriate liquids to finely disperse them. Unless liquid is used, particles tend to coalesce, forming a larger particle or aggregate, the size of which exceeds several tens of nanometers as a powdered sample. First we introduce the normal gas evaporation technique to show the principle of aerosol method. Then several modifications are described to get dispersed metallic systems as a colloid. 

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