The air you breathe in a train station is 15% human skin.
If you thought leaving the train station will save you from inhaling skin, just so you're aware about 80% of the floating specs you see in a sun beam are also skin.
Air is monitored at hundreds of sites around the world. It's usually presented as a mass to volume ratio, micro grammes per cubic metre, or by volume as parts per million. The main one for 'dust' would be particulate matter smaller than 10 microns, and a value of 100 ppm for particulate would be very high, even at a London roadside. The graph below shows the levels in Beijing that caused so much concern prior to the Olympics.
For the 15% figure to be accurate, that would equate to 150,000 parts per million, just for skin, so would be an even higher figure when the other emissions and size fractions were added.
Basically, it sounds like nonsense, or more clarification is needed on how they reached their conclusion.