Size cuts, aerosol measurements

When sources are studied, several things should be done to provide data needed for receptor-model applications. First, particles should be collected In at least two different size fractions corresponding to the division at about 2.5-ym dlam now used In many studies of ambient aerosols. In some cases. It may be desirable to have more size cuts. As noted above, compositions of particles from coal combustion change dramatically below about 0.5-pm dlam (44, 46). Above we Identified a minimum of about twenty elements that should be measured. Also, In order to develop adequate markers for sources that emit carbonaceous particles, measurements of organic compounds and other properties related to carbonaceous particles should be made. 

To study the potential health effects of pollutants in crowded spaces for recreational activities, particle mass versus size distribution of an ambient aerosol have been measured using a 10-stage Quartz Crystal Microbalance cascade impactor system (Junker et al. 2000). This impactor system consists of a series of 10 aerodynamic inertial impactors capturing particles at a mid-point cut-off ranging from 0.07 to 35 mm, arranged in a cascade with jets, which segregate the larger aerosol particles on top. 

Due to their simplicity of construction and use and the relatively sharp cut-off characteristics, cascade impactors have been widely used for the size classification and size-classified chemical analysis of aerosols. Table 6.1 lists the most important integrating sampling methods with their main characteristics. Table 6.2 gives the most important differential, size-resolving methods used to sample and measure atmospherie aerosol particles. The section of the particle size distribution and the modes that dominate the sensitivity of the methods are indicated. The upper and lower size limits are nominal values for the most commonly used forms of the techniques. Cost, complexity of operational requirements, calibration problems, and the demands of the particular evaluation to be used also affect the choice of methods. For example, chemical analysis usually requires that a sample be collected, then taken to the evaluation device. 

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