While the device used comes with six different size channels — 0.3, 0.5, 1.0, 2.0, 5.0, and 10.0 microns ( 1 micron is a millionth part of a metre) — a lot of the dust is so fine that aerosols in that range cannot really be measured. More than 98% of the dust, in fact, is contained in the first two channels (smallest particles) of size 0.3 and 0.5 microns. The study did not consider particles in these channels for the aerosol assessment. “But there’s a reasonable sized range where you can detect the aerosols,” Bonn said.
For validation, the researchers compared their measurements with those from specialised laboratory techniques. Aerosol concentration is often measured using a technique called laser diffraction, in which a laser beam passing through a sample lights up different-sized particles differently. Results from this highly specialised technique and the method used in the study, the researchers found, matched up perfectly.