To collect bioaerosols falling within a specific size range, impactors can be stacked to capture the variation of particulate matter (PM).  For example, a PM filter lets smaller sizes pass through. This is similar to the size of a human hair. Particulates are deposited onto the slides, agar plates, or tape at the base of the impactor. The Hirst spore trap samples at 10 liters/minute (LPM) and has a wind vane to always sample in the direction of wind flow. Collected particles are impacted onto a vertical glass slide greased with petroleum.
Variations such as the 7-day recording volumetric spore trap have been designed for continuous sampling using a slowly rotating drum that deposits impacted material onto a coated plastic tape. The airborne bacteria sampler can sample at rates up to 700 LPM, allowing for large samples to be collected in a short sampling time. Biological material is impacted and deposited onto an agar lined Petri dish, allowing cultures to develop.