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Results obtained from measurements of the concentration and size of particulate matter in air are dependent on the method used. Filtration samplers in conjunction with gravimetric analysis, as exemplified by the high-volume air sampler, represent the most commonly used technique in this country. The spot tape sampler and smokeshade devices have value in assessing the soiling properties of particulate matter, but are poor indicators of mass loading. Continuous monitors now available for measuring the concentration of atmospheric particulate matter appear promising, although further field testing is needed to assess their accuracy.
Devices are available for determining the size distribution of particles by number or by weight. Care should be taken not to interchange the results of a number and a weight distribution since they are not equivalent nor necessarily directly relatable. The author prefers cascade impactors for determining the weight size distribution because the fractionated sample is retained for chemical analysis and the respiratory portion can be assessed.
air, aerosols, samplers, particulate matter, membrane filters, integrating nephelometer, piezoelectric gages, beta particles, particle size, cascade impactors, light scattering, visibility
Deputy director, Pesticides and Toxic Substances Effects Laboratory, U. S. Environmental Protection Agency, National Environmental Research Center, Research Triangle Park, N. C.