And almost nobody is measuring them
https://www.bbc.com/future/article/20191113-the-toxic-killers-in-our-air-too-small-to-see“I expected a certain level of variation [in particle number]”, she says, “but the level of fluctuation really surprised me… The volume of cars that went past had very little impact on people’s exposure to PM2.5. But it had a massive impact on ultrafines.” As the volunteers pounded the pavements, they were exposed to a minimum of 36,000 particles at a time, up to a maximum of 130,000. When they took the same route by bicycle (tricky, but not impossible, with all the equipment), the maximums and minimums went up by another 20,000.
However, the highest averages were recorded inside the cars and buses: the closer to the source of the pollution, the exhaust pipes spewing out the fumes, the higher the total number of nanoparticles. The difference between walking by the kerbside of the road, and by the building side, on the same pavement – just a few short steps – was an average of 82,000 particles versus 69,000. The same readings registered no change in PM2.5.
