I just found this out while playing around.

On the LS400 Mk 4, if you hold down the recirculation button while turning the ignition on, the screen displays an adjuster for "SMOG" which presumably adjusts the sensitivity of the automatic recirculation system.

I had this on my old GS300 and also have it on my LS430. I have always found that no matter how sensative you set it, it always just seems to go to recirculate just that little but too late when you are following a bus or lorry.