The concentration of particles in the air is really small, so the mass units need to be really small as well. We commonly use micrograms instead of milligrams when measuring particle pollution
concentrations. We also need a lot of air, so we use a cubic meter instead of a liter of air. Imagine
a box of air that is one meter on each side. If my filter paper weighs 2.011 milligrams when clean
and 2.023 mg after I pump 1 m' of air through it, what would the concentration of particles be in
pg/m?