Still doesn't make sense to claim that "PM2.5" is a neurotoxin, depends entirely on what the specific particles are, not the size of them.

What is more dangerous, PM2.5 or PM10? Well, naturally, smaller particles are more harmful to humans usually, but without knowing what the particles are, it's impossible to tell. Just like "5ML is/isn't more dangerous than 10ML", it doesn't really tell us anything.