Comment by m463

I think the freeways are going from larger particles to smaller ones as DEF gets rid of the bigger diesel particles.

smaller stuff is more dangerous and goes deeper into your body:

- PM10: inhalable dust entering the nose and mouth.

- PM4: respirable fraction that can reach the gas-exchange region.

- PM2.5: fine particles that penetrate deep into the lungs.

- PM1: ultrafine particles with potential to translocate beyond the lungs.