Rotation impaction samplers are one of the most widely used mechanical devices for collecting air-borne particles in North America similar to Rotorod technology. Developed originally in the 1940’s, this technology has been shown to be equally effective at collecting particles with sizes ranging from over 100 microns to as small as 2 microns, and is therefore suitable for collecting pollen grains and fungal spores.

A basic rotation impaction sampler consists of two rods attached to a bar known as a “sampling head”, which in turn is attached to a motor. The rods are very thin (less than 2mm wide), and are coated with an embedding material such as silicone grease. As the motor spins, particles in the air impact against the leading surface of the rods and become embedded in the grease. As the rods spin in a circle, sampling occurs independently of wind direction. Wind speed is also independent, as rods travelling with the wind will come into contact with proportionally less air while rods travelling against the wind come into contact with proportionally more air. Standard practice in aerobiology is to sample at speeds of 2400RPM, providing the rods with a travel speed of over 80Km/h and further negating the effect of wind.

To determine the number of particles in the air over the sampling duration, a formula is used to convert the area of the collection surface to a unit of volume over time. In order to support this conversion formula, the number of rotations of the sampling head and the duration of sampling must be known. It is therefore very important that the speed at which the motor spins the sampling head is known and remains consistent. Analysis of samples is performed under a microscope, where particles of interest in a measured sample area are identified and counted. As the conversion formula provides a direct relation between the number of particles on the sample and the number of particles per unit volume of air, the methodology for sample analysis is straight-forward in both theory and practice.