Air conditioning units are not always suitable for improving air quality, for several reasons.

Most air conditioners are so-called split units. They do not exchange indoor air with outdoor air, meaning fresh air from outside is never transported inside.

While it may initially feel like fresh air, this is a misconception. Additionally, all air conditioners are equipped with rather dubious filters that at best filter regular household dust from the air. Fine dust and other pollutants are merely distributed within the room.

There are also air conditioning units that transport heat outside through a single hose. These, at least, remove CO2-laden air from the room. However, fresh air must come from somewhere. It is drawn into the interior through various gaps in the masonry. This can introduce all sorts of germs, bacteria, mold spores, gases, asbestos, and other components found in the masonry.

A rare form of air conditioning units are mobile systems set up outside, blowing cooled air into the interior. These are the only devices that essentially operate like a fan, blowing cooled fresh air from outside into the room. Typically, these also lack a fine dust filter. However, a suitable filter can most likely be attached to compensate for the unit's deficiency. The slight positive pressure created in the room over time removes all pollutants from the space.

Advantages

• If constructed properly as a fresh air supply unit, it can significantly improve air quality.

Disadvantages

• Often opaque functionality
• Usually lacks a fine dust filter
• Most units are split systems and therefore do not improve indoor air quality.