Sampling representative aerosol particles in fast-moving air is a challenging task. Aerosols are significantly more massive than gas molecules, thus they might not follow air streamlines well and could be more easily subjected to sampling errors. This work examines the physical factors that govern the aspiration efficiency of an aerosol sampling probe in unidirectional moving air, and explores the plausible sampling deviations under various high air velocity scenarios. The particle sizes of 0.5 and 5 μm are of particular interest due to their use in defining air cleanliness levels in ISO 14644-1[1] and FED-STD-209.[2]* Our analytical results indicate that significant sampling errors could occur for 5-μm particles when a thick-walled sampling probe is used, or when the air velocity at the sampling probe inlet does not match the velocity of the incoming air (i.e., anisokinetic sampling). The aspiration efficiency of 0.5-μm particles, on the other hand, is nearly 100% due to sufficiently small inertia of these particles.

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