You are very right, nanoparticles are particularly harmful to human health, and are often misrepresented by ug/m3 readings. The problem is that even A LOT of nano/ultrafine particles weigh very very little, so the numbers will appear similar or even the same regardless of different quantities.
The Laser Egg measures down to 0.3 micrometres and provides actual particle count, not just ug/m3 which allows for much clearer information. Although this is not in the very very small nanometer range, it's not bad. If you want to measure nanometre particles, unfortunately a big piece of very expensive equipment is still required.
Sand and salt will often be larger than PM2.5, and be in the PM10 rnage. You are right though, a better way of measuring and recording nanoparticles would be great! We'll keep working on it