I'd also like to point out that road wear is approximately proportional to the cube (^3) of the weight per axle on a vehicle, so cars are probably responsible for a minority of this pollution.
*edit: some are pointing out that the relevant road wear is proportional to the 4th power of vehicle weight, see the comments below for details.
And the paper: https://advances.sciencemag.org/content/6/36/eabb9785
I'd also like to point out that road wear is approximately proportional to the cube (^3) of the weight per axle on a vehicle, so cars are probably responsible for a minority of this pollution.
*edit: some are pointing out that the relevant road wear is proportional to the 4th power of vehicle weight, see the comments below for details.