If you are in traffic you will pick up fumes from the cars in front of you because the fresh air system picks up air just behind the hood near the windshield wiper panel.
Most cars today have virtually no smell but there are those cars with failing emissions systems that stink like old cars did, if you are behind an older car with a carburetor they smell the worst.
Makes me wonder how I'm still living, after breathing in all those fumes, from all those old cars I worked on and used since I was 13.
I tried turning off my fresh air in my Trax, what that does is fog the windows, after a little while and recirculates the air inside the car.
If you start to smell fumes you can turn off the outside air, but it does take a few minutes to notice the difference.