I feel the term "micro particles" is too broad. I'm pretty sure there is a difference for health between car exhaust particles, tire particles, brake pad particles, industry particles, fertilizer particles, wood smoke particles, etc. It all ends up in the same PM10 or PM2.5 or whatever category but the chemical nature is quite variable.
Not as big of a difference than you think. They're all rather bad, causing insults to cells and immune reactions - carcinogenic.
Additonally, resorbed into bloodstream they cause a variety of hormonal and kidney problems.
They can be roughly grouped into hydrocarbons, other plastics, aerosolized solvents, other absorbed aerosolized chemicals, inert particles.
How much worse are the bad ones than the others?
Indeed, but it will at least continue to reduce the size of the problem.