there are 200000x the number of private cars. are you sure?

Your estimate isn't even close--you're off by about 4 orders of magnitude.

Fact: In California, the number of trucks is about 300K vs cars at 14M (about 40x).

Fact: California AADT on roads for trucks ranges from a couple of percent up to almost 50%. Very few roads have less than 10% AADT from trucks.

Fact: Damage to roads goes as fourth power of axle load.

Speculation: Given that tires are the primary means to transmit that damage to the roadway, it wouldn't surprise me if the trucks are responsible for the vast majority of tire particulates.

Reference: https://dot.ca.gov/-/media/dot-media/programs/traffic-operat...

it's widely accepted that trucks cause the majority of road wear, considering the tire is the softer part in contact there, it seems pretty plausible

I don't have a citation to point to, though!

edit: there are roughly 100x registered passenger cars in the US as semis

A fully loaded tractor trailer has 5 axles and weighs 80,000 lbs, it does 9000-10000x more damage than a passenger car.

This is why states operate weigh stations — overweight trucks cause significant damage.

Semi’s drive 12+ hours a day most days of the year. Passenger cars just go to work and they store and back.