I have a Phillips Clean Air System 75.

It has a thin sponge type dust filter, then a much finer filter for smaller particles, then an activated charcoal filter that takes out smoke and some gasseous pollution, and finally it has an electric ionizing function that causes the tiniest particles to develop a static charge and cling to surfaces (especially computer screens).

It works well. Where I was living before the air was filthy and I would have to change the filter cartridges every three or four months.

Now that I live in the country, I hardly ever use it unless there is smoke in the house.

The biggest nuisance is the noise.