Why would I say I can smell cigarette smoke when I can't? Unless a car has it's ventilation system on 'recycle' it takes in air and expels air, and just like you can smell the diesel fumes, your car is taking in some the air from the car(s) in front, and as I said, if I'm overtaken and the car moves in front of me, I can clearly smell cigarette smoke if it's being emitted. Why do you wish to challenge that?