Physical behavior and sampling of airborne particles

Airborne particles form a colloid consisting of a gaseous dispersion medium and dispersed particles, which may be solid or liquid. Liquid particles are always spherical, since the surface tension is much larger than frictional forces. Solid particles show a variety of shapes such as spheres, regular polyhedrons, straight and curved fibers, flakes, and irregular particles. Particles that are approximately the same length in all directions are called isometric.