Can the unit be mounted in a window?

there is no reason why not if the outside part is properly weatherproofed and screened to stop insect etc ingress - easier may be to duct the unit to a hole in a window - use at least 125mm/5inch ducting and dont make it too long.

It is not recommended to run the unit in this way, however, as you will almost certainly find that the filters etc will block very quickly due to many more airborne particles(especially living ones) in outside air (depending on your situation) and the fact that inside a room with the unit running you have a relatively closed system that will steadily get cleaner as you use the unit. best way to test this would be to run the unit normally but outside for a while to see if it functions ok.

Hope this helps - i cant see that you would gain anything from running the unit in a window apart from higher filter replacement costs :)