I bought an air ioniser at the local boot sale. The gadget in question came with a marvelous little detector that lights up when you wave it around near the ioniser to show that it is working. I noticed that the area around it gets very dusty.
Ionisers create a static charge around airborne contaminants. Once charged with static, these simply stick to the nearest surface they find. The air feels fresh because the contaminants are no longer floating around but are stuck to the walls, furniture, carpets and table tops.
Phone masts, transmitters and electrical transformers are all firing out ions at quite a rate and having a similar effect to the ioniser. If a phone mast is downwind of a source of pollution like a busy motorway, then downwind of the phone mast might not be the healthiest place to live.