Cabin Air Filter / Purifier: Description and Operation

Dust and Pollen Filter with Activated Charcoal Insert

• There are different versions of the dust and pollen filter (with and without an activated charcoal insert). Refer to the Electronic Parts Catalog (ETKA). An Audi TT with A/C has a dust and pollen filter with an activated charcoal insert is installed. An Audi TT without A/C has a dust and pollen filter without the activated charcoal insert.

• The activated charcoal filter element functions as a dust and pollen filter, however in addition the activated charcoal filter can also filter out gaseous pollutants, for example, ozone, benzene, nitrogen dioxide from the air flow. The basic task of the activated charcoal layer in the dust and pollen filter is to keep load peaks out of the passenger compartment.

• The activated charcoal also has the task of removing certain gaseous contaminants from the air flowing through. The activated charcoal layer in the dust and pollen filter reacts differently to various pollutants in the air.

- Certain pollutants bond permanently in the active-carbon layer.

- Others are converted into noxious bonds like in a catalytic converter.

- For the rest, the activated charcoal works as a condenser (capacitor). With increasing load pollutants are absorbed, until a certain saturation is reached. If the amount of pollutants decreases, the activated charcoal layer continuously releases the absorbed particles.

• Because a portion of the gaseous pollutant particles as well as dust and pollen bond permanently to the activated charcoal layer, it may be necessary for the following reasons to change the dust and pollen filter earlier than planned on vehicles that operate in areas with high levels of pollution:

- the activated charcoal layer in the dust and pollen filter is saturated faster than planned.

- a saturated filter can no longer absorb pollutants and the pollutants can flow through freely.