Well - there is actually an incredibly complicated way you "could" make it to a smoking atrium without leaving T4 security (though you might have to tackle a gate agent or two to make it work).

In theory you could go through security at T4, then take the American Eagle bus over to the AE remote terminal, then take the Alaska bus from there over to Terminal 3 - then hike backwards toward T3 security - and you will find an atrium (which - I think is smoking permitted - though I have never checked that fact). Then of course make it back the same way - all while hoping the various gate agents on your way to T3 wont check your boarding pass (of course returning to T4 wouldn't be a problem).

I guess you would have to be ultra desperate to go through it (or maybe pathologically afraid of airport screeners) - and probably the faster way to get your smoking "fix" would probably be to just exit T4 security and walk some distance toward the Tom Bradley intl terminal on the departure level side walk, and hope no cops harrass you for smoking too close to the building

BB-Miler