There are 4 ways a filter captures airborne particles. Below you will see the airborne particle in red. the filter fibers/media in black. and the air stream/flow as an arrow. The air stream will continue as the filter media stops the particle.
Sieving: This is when the particle matter is physically too large to pass through the filters fiber spaces.
Impaction: This method works on those large. heavy particles that are in the air stream. Since these particles are heavier than the air stream that carries them. as this air stream slows down due to it hitting the filter media the heavy particle continues in a straight line (like a slingshot) and collides with the filter media were it is trapped and held.
Diffusion:This method works on the smallest particles. Essentially as these particles move through the air stream they collide with the fiber and are collected by the filter fibers.
Interception: This process works on mid-size particles that are too large for diffusion and too small for impaction. As these particles pass through the filter media they are captured or intercepted when they touch the filter fiber.