Here's my verdict, a conclusion that I came to after a a few months of close observation:
The morning following a car drive or bike ride in moderate to heavy traffic - my spit has a brown tint.
Do you want to take a guess what that is from? ICE (internal combustion engine) exhaust.
I am going to be changing where I live to a low populated area because of this.
The only other option is to wear an air tank or a mask that filters out all those particulates while on the roads.
This is the reality of our oil dependent society. It's not worth it in my opinion. Who knows what health risks we face as a result.

The morning following a car drive or bike ride in moderate to heavy traffic - my spit has a brown tint.
Do you want to take a guess what that is from? ICE (internal combustion engine) exhaust.
I am going to be changing where I live to a low populated area because of this.
The only other option is to wear an air tank or a mask that filters out all those particulates while on the roads.
This is the reality of our oil dependent society. It's not worth it in my opinion. Who knows what health risks we face as a result.