Every air conditioning unit has a filter. The type of filter depends on the type of air conditioning system. A system with integrated ventilation requires a less effective filter. 
The efficiency of a filter is measured in the percentage of arrestance of particles. Simply stated: what amount and size of particles do they stop?
Another factor in the efficiency of a filter is the air flow, or simply stated; the fan speed which defines how many m³ of air goes through the filter.

Dust filter

Removes airborne dust and particles to ensure a steady supply of clean air. Can easily be washed or vacuumed.

Air purification filter

The air purification filter traps small dust, particles and pollen as small as 0,01 microns and prevents the propagation of bacteria and virusses. The filter is double-sided with an air-cleaning electrostatic filter on the front side and a deodorising activated charcoal filter on the rear side. The air purifying filter is always combined with a regular filter.

This filter is an anti-bacterial and deodorising filter which powerfully decomposes cigarette and pet odours and also restrains the reproduction of bacteria, virusses and microbes caught in the filter. The photocatalytic deodorising filter is always combined with an air purifying filter.