Aerosol classification

The composition distribution of the particles produced in a laboratory pulverized coal combustor will be explored in this paper using aerosol classification techniques capable of resolving the composition distribution to 0.03 ym diameter. Unlike previous attempts to measure the composition distribution, the particles were classfied directly, without having to resort to resuspension, using calibrated instruments. Experiments were conducted in a laboratory combustor in which operating parameters can be varied over a wide range. Data are presented which demonstrate that the composition of fine particles varies substantially with combustion conditions and does, under some conditions, differ considerably from that of the bulk ash. 

Jillavenkatesa, A., Dapkunas, S.J., and Lum, L.-S.H., Particle Size Characterization, National Institute of Standards Technology Washington, D.C., 2001. Knutson, E.O., and Whitby, K.T., Aerosol classification by electric mobility apparatus, theory, and applications, J. Aerosol Set, 6, 443, 1975. 

Aerosol products are designated as Level 1, 2, or 3 by the classification system of NFPA 30B, Code for the Manufacture and Storage of Aerosol Products. Level 1 aerosols are considered the least hazardous and Level 3 the most hazardous. This system is based upon the fire hazard of these products. Other hazards such as the acute and chronic health hazards, as well as the environmental hazards of aerosol products are not addressed by the NFPA 30B classification system. The fire hazard associated with aerosol products is determined by either a 12-pallet aerosol classification test or the chemical heat of combustion of all of the constituents within the aerosol can. 

The other method of classifying an aerosol product is by determining the chemical heat of combustion of all of the constituents within the aerosol can. This method provides consistent correlation with the 12-pallet aerosol classification test. The chemical heat of combustion is the product of the theoretical heat of combustion and combustion efficiency. An aerosol product is considered Level 1 if the chemical heat of combustion is greater than 0 and less than or equal to 8600 Btu/lb (20 KJ/g), Level 2 if it is greater than 8600 Btu/lb (20 KJ/g) and less than or equal to 13,000 Btu/lb (30 KJ/g), and Level 3 if it is greater than 13,000 Btu/lb (30 KJ/g). NFPA 30B requires that the classification of an aerosol product be stated on the carton to allow easy identification. 

Knutson, E.O., Whitby, K.T., Aerosol classification by electric mobiUty Apparatus, theory, and applications. J. Aerosol. Sci. 1975, 6, 443. 

An aerosol which is flammable in accordance with paragraph 2 or Part III of Schedule 1 shall have the classification of a flammable gas. Other aerosols need not be classified as flammable gas or flammable liquid. 

I. Bondarenko, H. Van Malderen, B. Treiger, P. Van Espen and R. Van Grieken, Hierarchical cluster analysis with stopping rules built on Akaike s information criterion for aerosol particle classification based on electron probe X-ray microanalysis. Chemom. Intell. Lab. Syst., 22 (1994) 87-95. 

M. ICRP (1995) recommends assigning all americium aerosols to Type M in the absence of specific information supporting an alternative classification. 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

See also Axial dispersion aerosols, 1 774-775 aqueous, 18 292 behavior of, 15 685-690 chemical processing aids, 8 705-711 chromatic, 11 134 classification, 8 698-699 colorants for plastics, 7 360-361 donor-acceptor interactions, 8 707-708 electrostatic repulsion, 8 732-734 in filled networks, 22 572 of filled polymers, 11 307-308 flow, 8 726-730 flushing, 8 711... 

Cluster analysis Is used to determine the particle types that occur in an aerosol. These types are used to classify the particles in samples collected from various locations and sampling periods. The results of the sample classifications, together with meteorological data and bulk analytical data from methods such as instrunental neutron activation analysis (INAA). are used to study emission patterns and to screen samples for further study. The classification results are used in factor analysis to characterize spatial and temporal structure and to aid in source attribution. The classification results are also used in mass balance comparisons between ASEM and bulk chemical analyses. Such comparisons allow the combined use of the detailed characterizations of the individual-particle analyses and the trace-element capability of bulk analytical methods. 

A Guidance Document on Acute Inhalation Toxicity Testing is being developed and presently exists as a draft (OECD 2004b). The document recommends the Acute Toxic Class (ATC) Method with a group size of three animals per sex, if the objective of the test is solely related to hazard classification. Limits for particle-size distribution of aerosolized test substances are suggested. The preferred mode of exposure is the nose-only, head-only, or head/nose-only exposure technique, because this mode of exposure minimizes exposure or uptake by noninhalation routes. 

Phares, D. J. Collection of Ultrafine Aerosols by Electrostatic Classification for Size-Resolved Chemical Analysis. Proceedings of the 233rd American Chemical Society National Meeting, Chicago, IL, March 25-29, 2007. 

Aviado DM Toxicity of aerosol propellants in the respiratory and circulatory systems. X. Proposed classification. Toxicology 3 321-332, 1975... 

Microscopic Identification Models. Many different optical and chemical properties of single aerosol particles can be measured by microscopic identification and classification in order to distinguish particles originating in one source type from those originating in another. The microscopic analysis receptor model takes the form of the chemical mass balance equations presented in Equation 1. 

Source contributions assigned to the same aerosol sample have varied greatly in intercomparison studies (23) but, without the intermediate particle property classifications, it is impossible to ascribe the differences to the analytical portion or to the source assignment portion of the process. 

Bentz, J. W. G J. Goschnick, J. Schuricht, H. J. Ache, J. Zehnpfen-nig, and A. Benninghoven, Analysis and Classification of Individual Outdoor Aerosol Particles with SIMS Time-of-Flight Mass Spectrometry, Fresenius J. Anal. Chem., 353, 603-608 (1995b). 

Aerosol Heterogeneity. The variation of the chemical composition from particle to particle within an aerosol size class has been probed in a number of ways. Single-particle chemical analysis has been achieved by using the laser Raman microprobe (25) and analytical scanning electron microscopy (26). With the electron microscope techniques, the particle can be sized as well as analyzed chemically, so the need for classification prior to sample collection is reduced. Analyzing hundreds to thousands of particles provides the information necessary to track the particles back to their different sources but is extremely time consuming. 

Aerosol Instrument Classification. Friedlander (34) classified the range of aerosol instrumentation in terms of resolution of particle size, time, and chemical composition. This classification scheme is illustrated in Figure 3. The ideal instrument would be a single-particle counter-sizer-analyzer. Operating perfectly, this mythical instrument would fully characterize the aerosol, with no lumping of size or composition classes, and would make such measurements sufficiently rapidly to follow any transients occurring in the aerosol system. 

Figure 3. Classification of aerosol instruments in terms of their inherent time, size, and composition resolution. (Adapted from reference 34.)...

---