Stinking Air We breathe

On many occasions, we will travel behind a classic or vintage car, and the stink that comes off it from the exhaust is horrendous. Now, as an automotive technician and a classic car enthusiast, I know the reason why; however, that's not really my point.

I worry about the polluted air we breathe, and it's not necessarily the odd classic car you see or smell, because many of us were brought up with these stinking things and never thought much of it. But today seems to be different. Question: Is the air we breathe getting heavier, so that we all notice it more? Or is it my imagination, and these nice-looking classics are all running a little rich?