High volume cascade impactor

Aerosol particles enter the high volume cascade impactor through the parallel slots in the first impactor stage, and particles larger than the particle cut-off size of the first stage im- 

---

Table III. Median Aerodynamic Diameters (MAD) and Geometric Standard Deviations (Og) of Pb-210 and Be-7 Based on Radioactivity and SO Measured with High-Volume Cascade Impactors...

Particles that can be inhaled, those less than 10 p,m (10,000 nm PMIO) can be separated by the high volume cascade impactor (HVCI) into four fractions. When the HVCI was used to collect organic urban aerosols presumably from transportation, combustion, and the Earth s crust, the breathable particulate matter (PM) was divided into PM 10 to 2.5 p.m (coarse aerosols, which are mechanically produced), and the PM 2.5 to 1 p.m (intermodal) fiaclion, which is expected to have particles that contain properties of both coarse (larger) and fine (smaller) aerosols. In addition it separates the PM 1 to 0.2 p,m (1000 to 200 nm accumulation) fraction (just larger than nano- or ultrafine particles with properties similar to those particles) and PM 0.2 (particles <200 run diameter in air) firaction. The cutoff size (200 nm) was chosen for convenience. 

Quality of measurement When the Harvard high volume cascade impactor was compared to the virtual impactor, fine (PM 2.5 to 0.2 2500 to 200 nm) material and coarse (PM 10 to 2.5 10,000 to 2500 nm) material masses in the respective fractions were within 10% of agreement with values from other methods of collection and particle sizing. Measurements were simpler to make with the Harvard impactor. However, chemical constituents appeared to be sufficiently variable within fractions that activity should be measured on the material used to expose whole animals, or cells (5). 

The former approach, attempting to measure the droplets in their fully hydrated state, has enjoyed more widespread use. Experimentally, this has been accomplished in a number of ways. The use of low-flow impactors that entrain minimal quantities of ambient air and hence maintain the quasiequilibrium humidity exiting the nebulizer is one approach (30). Adding humidified dilution air, rather than ambient air, to a high-volume cascade impactor is another. Cooling the impactor to the same temperature as the nebulizer cloud (reservoir) has also been shown to be an effective way of providing sufficient stabilization for aerosol measurement purposes (31). However, a technique that has been used extensively in conjunction with a large number of deposition studies is laser diffraction (3). As described above, this technique measures the physical diameter... 

High-volume cascade impactors This technique consists of a stack of five 30 cm-diameter plates, each with 300 jet orifices, mounted over a standard high-volume glass fiber filter. The collection medium is perforated sheets of aluminum foil or glass fiber mounted on aluminum plates. Particle size fractions greater than 7 pm and less than 1.1 pm are collected at a flow rate of 0.561 min... 

Because of the health impUcations of airborne particles, a large number of techniques has been developed in recent years for sampling fine and coarse particles. The most sophisticated, a high-volume cascade impactor, can separate particles into five or more size classifications between about 0.1 and 15 pm. These instruments are labor-intensive and usually provide much finer detail than is needed for evtduating environmental severity with respect to particles. 

Rdbig et al. (1980) reported that the distribution of the long-lived radionuclide Be was shifted to large particle sizes due to long residence times of Be in the atmosphere. An equivalent aerodynamic diameter of about 0.65 pm for Be might have resulted from the plot of the activity size distribution of the ambient air obtained by a high volume cascade impactor... 

Fig. 2.8. Aerodynamic size (Dp) distributions of radionuclides R) and SO (Af) derived from a 7-day aerosol sampling made using two high-volume cascade impactors, HVI. Pb-212, and were only measured on...

For Be measurements with high volume cascade impactors (HVI), even with 1 ACFM cascade impactors, the plates are leached with 0.1 M HCl and the activity of Be is measured with coaxial Ge y-detectors through the gamma photons of energy 477 keV. 

---