Traditional particle size determinations for aerosols below 0.1 μm diameter have been made by both electrical mobility and diffusional methods. Difficulties in determining particle size spectra in the sub-0.1 μm diameter range arise when air from microelectronics manufacturing cleanrooms is sampled because of the low concentration of particulates and the low sampling rates of currently available instruments. Previously reported data indicate that the differential electrical mobility method does not provide reliable aerosol distributions for concentrations below about 1 particle/cm3. Laboratory and operating cleanroom measurements with the collimated hole diffusion battery gave particle distributions spanning the range from about 0.001 particles/cm3 to 1 × 105 particles/cm3. The low concentration particle spectra in cleanrooms at rest showed peak aerosol concentrations at about 0.1 μm with few particles at sizes below this peak.

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