Occasionally, I cross the street after a trash truck has gone by and I am hit by the “air wake.” I then wonder if that air contains more germs and carcinogens than normal air. To expand the question further, is the air in and around dumpsters and trash cans more unhealthy for you than normal air?
I also wonder about the possible unhealthy effects of the chemical smelling air when I walk down the detergent aisle in the supermarket.
I can give a first hand experience about the detergent aisle.
Back in high school, I worked at the local supermarket, and ran track. The market was right next to the school, and I’d go to work directly from track practice (after showering).
On days that I’d end up with “aisle 9’s” stocking cart, I knew that I’d have a long shift ahead. The smell from the detergents and soaps would irritate my lungs something fierce. On days that I didn’t have track practice, that aisle was no problem at all, though I hate the smell, and to this day, hold my breath as I go down the “soap aisle” to get what I need.
I don’t think it was “unhealthy” as such for me, but could be if you had an extreme sensitivity to perfumes and the like. Normal, healthy lungs, not irritated from extreme use or other condition, should be just fine.
As for “trash air,” I’d not want to spend any extended time in that environment, but it’s probably not that much more “germy” than the air you’re normally exposed to. It certainly does stink though, so for that reason, I’d prefer to spend as little time in it’s presence as possible.
Of course, if you take it to the extreme, I’m sure some sort of fireman’s mask, with an independent air supply via tank, or filtration device, could be rigged for your day to day use. 
Nothing is germ free.
Anytime you smell anything you are taking a small amount of that substance into your body. Does that always mean germs, no, but it indicates the possibility.
Normal household trash is not likely dangerous to smell. If it were, trash truck workers would wear respirators.
You’re inhaling far more carcinogens just from other vehicles exhaust than you are from following a trash truck close enough to smell the trash.
There is always the possibility that someone tossed out a bag of loose asbestos, but your car has air filters…I can’t say for sure one way or another that the extreme cases are safe or unsafe or where that line is drawn.
If you’re not sure, don’t follow so close.
I once brought home a box of Bounce in the same grocery bag with a loaf of French bread wrapped in a paper bag. By the time I got home, the Bounce perfume had permeated the loaf of bread so much it was inedible. The stuff is so strong, I would be very very afraid of inhaling it. Just look at the effects of aerosolized artificial butter at the microwave popcorn factories.
Why would urban garbage be an elevated carcinogenic risk? It might carry disease bacteria, but cancer is generally not caused by bacteria.
Municipal solid waste can absolutely contain carcinogens. They come from batteries, pesticides, paint, adhesives, plastics, etc.
See table 6B.1 here:
However, I would say that intermittent contact with a dumpster or garbage truck is not dangerous. Living near a landfill or municipal solid waste incinerator might be more risky.