Although it's fashionable to assert that pollution causes every imaginable ill effect, there needs to be a causal chain. In this case, "air pollutants induced inflammation, cell death and the buildup of amyloid protein in the brain".

That chain is not intuitive (and not predicted), thus, "Surprising."

Particles going into your lungs to produce cognitive effects is the basis behind smoking cigarettes, marijuana, meth, etc.

Nicotine, THC, etc. are the active ingredients expected to cause cognitive effects.

The particles are regarded as particularly unwanted--especially by marijuana users.

This is the whole idea behind vaporizers.