You do know that a carbon filter will take out smells like farts and volatile organics and stuff like that as well as cooking smells? They also take out ozone which may be a problem if he has an old laser printer and hasn't fitted a new filter for years.
You can buy mats for aquarium use which I have fitted to my dehumidifier while decorating to get rid of the paint smell faster.
Even my car has a carbon filter to remove some of the smells from that dirty diesel in front. Not that it has enough carbon in it to last long.