> Using a popular family hatchback running on brand new, correctly inflated tyres, we found that the car emitted 5.8 grams per kilometer of particles. >Compare

> Using a popular family hatchback running on brand new, correctly inflated tyres, we found that the car emitted 5.8 grams per kilometer of particles. >Compared with regulated exhaust emission limits of 4.5 milligrams per kilometer, the completely unregulated tyre wear emission is higher by a factor of over 1,000. This is approximately as reasonable as declaring that a crossbow is more dangerous than a gun because it fires a heavier projectile. How large are the particles? What's their expected lifetime in the atmosphere? What proportion are smaller than 10 micron? 2.5 micron?