The following literature review(2014) mentions an estimate of 0.1-10% tyre wear becoming airborne - because the majority is relatively large particles:
https://publications.jrc.ec.europa.eu/repository/bitstream/J...
That doesn't mean they're right, but it's the only way I can interpret what they're saying.
The following literature review(2014) mentions an estimate of 0.1-10% tyre wear becoming airborne - because the majority is relatively large particles:
https://publications.jrc.ec.europa.eu/repository/bitstream/J...