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...