One final thought from the conference. At the David Lawrence Convention Center, there is a ground floor that is split in two by a roadway allowing taxis and buses (and cars) to pick up and drop off people. I'm sure that some of these vehicles wait there, idling all the while. One the walls, as you walk to the doors, are the No Smoking signs.
Because we all know that smoking is bad for you, but exhaust fumes are just fine.