More and more trains are being fitted with ion air cleaning systems (in this case Sharp's Plasmacluster technology). I don't know why we don't have much in the way of air cleaning in the west... Dyson just released a fan with a filter in it, for example, but only in Japan. I have a few cleaners, mostly Plasmacluster but also Panasonic Nanoe, and I find they really help with allergies.
They also keep smells down, so I have a small one by my shoes and one for the cat tray. They kill all the bacteria that produce odours.
For some reason we really don't seem to go in for quality of life products here. Companies don't even try to sell them to us.