DRUM Impactors separate particles by size and time

Since 1945, aerosol scientists have used cascade impactors to collect size segregated aerosol samples. A DRUM impactor is a special type of cascade impactor developed by the University of California's DELTA Group. In addition to separating aerosols by size, DRUM impactors using a rotating drum disk impaction surface to record time.


What is a cascade impactor?

A cascade impactor is an aerosol monitor that segregates particles into multiple sizes by using the particle's inertial forces. In a cascade impactor, an isokenetic airstream enters the sampler, passing through a specially-sized orifice. The airstream takes a sharp turn away from a perpendicular impaction surface. Larger particles, with greater inertial force impact; smaller particles, dominated by the viscus forces of the airstream, continue to another stage. In subsequent stages, the orifices have lower pressures and higher velocities, allowing smaller particles to impact.


  • Particle size is important for evaluating particle transport. Large particles settle quickly from the atmosphere, whereas nano-particles remain in the atmosphere and travel across continents.
  • Human health effects depend on particle size. Larger particles impact in the nasal cavities. Fine particles, 1 micron in diameter, pass through the larynx and clog the alveoli of the lungs. Nanoparticles may enter into the boodstream and pass the blood/brain barrier.


  • Extreme events may pass quickly, but are often the most damaging to living systems.
  • Temporal cycles are evident, when samples are taken continuously. See pollen emission, day/night cycles, traffic, seasonal changes, etc.
  • Peak concentrations can be traced back to their source using HYSPLIT trajectory models.