How does an air purifier take particles out of air?

Air in a room can carry small solid particles and liquid droplets. Dust, pollen and smoke include particles of different sizes. A common air purifier uses a fan to pull room air through a filter and return filtered air to the room.

A fibrous filter is a mat of fine strands. Air travels through spaces between them. Some larger particles cannot follow the air as it bends around a fiber and collide with it. Very small particles wander as air molecules bump them, bringing some into contact with fibers. Particles passing close enough can also touch and stick.

The particles that stay in the filter have moved out of the airflow. They have not vanished. Particles retained on the fibers are separated from those still carried by the outgoing air. Repeated circulation brings room air through the filter again, allowing further capture while the collected material stays behind.

Particle capture is one specific kind of cleaning. Removing a particle does not mean killing microorganisms on it. Gases behave differently from suspended particles; some purifiers include a separate material such as activated carbon to adsorb certain gases. How much room air reaches the filter, how effectively it captures particles, and new particles entering the room all affect the resulting air.