= Particulate Matters – it is a mixture of solid particles and liquid drops in the air. Some particles as a dust, dirt, soot or smoke are large or dark enough to be seen by naked eye. Others are so small they can be visible only using a microscope.
= particulate matters with diameter of 10k µ (micrometre) and less
=particulate matters with diameter of 10k µ (micrometre) and less, humar hair has on average 70 µ, so the matter PM2,5 is circa 30x smaller
= size of particulate matters