Smoke travels upwards, and if smokers are confined to the top level and adequate ventilation is in place (be it an open window or a small fan), then there can be no cause for concern to those non-smokers who sit downstairs.
One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.