Yes, a lot smaller. pm is for picometer, PM is for Particulate Matter.
118 pm = 118*10-12 m = 1.18*10-10 m.
PM10 is 10 micrometers = 10*10-6 m = 10-5 m.
So PM10 is 100,000 times as big as an atom in diameter.
Yes, PM is nothing to do with pm. Confusing, but to keep these units in order, they go down in factors of 1,000:
1 metre = 1000 millimetres (mm)
1 millimetre = 1000 micrometres (µm)
1 micrometre = 1000 nanometres (nm)
1 nanometre = 1000 picometres (pm).
So the atomic diameter (twice the atomic radius) of those metal atoms is in the range of about 200 to 400 picometres, or 0.2 to 0.4 nanometres.
Using the same units, PM10 is 10,000 nanometres, which may be easier to read than the scientific notation above.
Edit to add: the same prefixes apply to all SI units, including grams (see the common milligram/microgram confusion in aluminium readings!)