At least one book I have read about the rise of plastics said that during the worst years of rubber shortages in WW2 there were serious proposals to scrape roads and recover tire materials in the USA. I believe the discovery of stable artificial rubber materials, capable of being produced in volume in time for the D Day landings helped with the supply chain crisis as the armed forces moved forward (the rate of supply became a major issue and logistics demands were high)

While that is true it that has little to do with smog. Smog is air contaminants.

What do those “other contaminants” that aren’t tailpipe emissions have to do with smog?

They contribute to the smog

Most of them don't - they are heavy particulates that fall to the ground.

I've heard that break dust is also really carcinogenic.

Brake pads used to be made of asbestos, but that’s been phasing out since the 1990s. Now it’s pretty rare.

Gotcha, so the newer materials are not as bad then, I am guessing?