[wongarsu]

To humans, the exhaust of an internal combustion engine is a much bigger concern, car tire particles are comparatively heavy, so they stay lower and settle out quicker.

Of course then they get washed away and end up in rivers and oceans, and we should do something about that. Probably there are a lot of low hanging fruit for that left, simply because historically nobody cared about it, apart from the inconvenience of needing to buy new tires.