This factor is important in the design of inertial samplers, or impactors, as described below. The ideal impactor is depicted in Figure 4, and consists of a laminar airstream turning before a plate. This defines the probability of a given size particle impacting the plate under a given airflow. The collection efficiency is affected by the adhesion of the surface, particle bounce, and particle shape. Particle Shape Bioaerosol particles have a diversity of shapes, including spherical, dodecahedral, needle-like and flakes.
Many viruses are pleomorphic and change their shapes.
Most sampling methods rely on the definition of aerodynamic diameter, or the diameter of a spherical water droplet which settles at the same rate as the particle being sampled. This is only one of several different equivalent diameters, the use of which is dictated by the sampling method. These may include the equivalent volume diameter, the equivalent surface diameter or the equivalent electrical diameter. Particle shape is a fundamental property and is important in assessing health hazards and interpreting data from some sampling methods. The shape frequency distribution can be developed using Fourier analysis of the signature waveform, of which the first five harmonics represent the basic shape, and the higher harmonics describe the texture of the surface.