South Florida Indoor Air Quality - Air Filtration Principles:
Four different collection mechanisms govern particulate air filter performance: inertial impaction, interception, diffusion, and electrostatic attraction. The first three of these mechanisms apply mainly to mechanical filters and are influenced by particle size.
Impaction and interception are the dominant collection mechanisms for particles larger than 0.2‚ µm, and diffusion is dominant for particles smaller than 0.2 µm. The combined effect of these three collection mechanisms results in the classic collection efficiency curve, shown below. The information on this page is adapted from a National Institute for Occupational Safety and Health whitepaper entitled: "Filtration and Air-cleaning Principles."