Although plastic particles in the air are increasingly coming into focus, knowledge about their distribution and effects is still limited. Chemical analyses from Leipzig now provide details from Germany for the first time: Around 4% of the particulate matter consists of plastic. Around two-thirds of this comes from tire abrasion.
I don’t think we’ve used tree rubber in our car rubbers in a long time
Correct, it’s all been synthetic for a long, long time. And for what that’s worth, even if there were enough sources of natural latex in the world to support the global tire industry, we’d still have problems. In both cases, polymers are stabilized with sulfur in a process called vulcanization. I’m mostly sure that’s why tires don’t decompose under natural conditions.
People are working on it though: https://pmc.ncbi.nlm.nih.gov/articles/PMC11041115/