Hi,
Here is how I understand your sentence.
1. rushing past >> this sets the scene, describes what was happening while they were walking. You could read it as "
while heavy traffic was rushing past", if you like.
2. with little if any thought to the damaging pollutants >> they didn't think much
(with little) about those pollutants they were inhaling; they probably didn't think at all
(if any) about them.
"
With little if any + noun " (Hmm, I think it needs a comma before "if") is one of those chunks worth learning. It means without, or with a very small quantity/amount/number etc of something.
Hope my interpretation is fine. If it's not, somebody will correct it.
