it was a 2007 toyota matrix i was driving for the lab my wife runs. it also came with a hepa filter(and had 6K miles and 6 months on it), so i kept the windows up and the ionizer on. the hepa filter took out the hydrocarbons from the diesel trucks. those things are more dangerous than people know, as usual.
the ionizer i used was the ionic breeze from sharper image. i am sure there are others to choose from.