The contribution of tire and brake pad wear is really quite low compared to other sources of air pollution.
From Evangeliou et al. (2020), Atmospheric transport is a major pathway of microplastics to remote regions, page 3:
"Surface concentrations of tire wear particles (TWPs) range between a few ng.m−3 and 20 ng.m−3 for PM2.5 and up to 50 ng.m−3 for PM10 (Supplementary Movie 1). Brake wear particle (BWP) surface concentrations reach 50 ng.m−3 at maximum (Supplementary Movie 1). The highest concentrations were calculated for eastern USA, Europe and South-eastern Asia. All concentrations (TWPs 0.4 μg.m−3 for PM2.5, 1.8 μg.m−3 for PM10; BWPs 0.8 μg.m−3 for PM2.5, 1.4 μg.m−3 for PM10) were far below air quality limits for PM (annual mean 10 μg.m−3 for PM2.5, double for PM10) and lower than typical black carbon (BC) concentrations in remote regions."
From Evangeliou et al. (2020), Atmospheric transport is a major pathway of microplastics to remote regions, page 3:
"Surface concentrations of tire wear particles (TWPs) range between a few ng.m−3 and 20 ng.m−3 for PM2.5 and up to 50 ng.m−3 for PM10 (Supplementary Movie 1). Brake wear particle (BWP) surface concentrations reach 50 ng.m−3 at maximum (Supplementary Movie 1). The highest concentrations were calculated for eastern USA, Europe and South-eastern Asia. All concentrations (TWPs 0.4 μg.m−3 for PM2.5, 1.8 μg.m−3 for PM10; BWPs 0.8 μg.m−3 for PM2.5, 1.4 μg.m−3 for PM10) were far below air quality limits for PM (annual mean 10 μg.m−3 for PM2.5, double for PM10) and lower than typical black carbon (BC) concentrations in remote regions."
https://www.nature.com/articles/s41467-020-17201-9