PM_x

= 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.

PM₁₀

= particulate matters with diameter of 10k µ (micrometre) and less

PM_2,5

=particulate matters with diameter of 10k µ (micrometre) and less, humar hair has on average 70 µ, so the matter PM_2,5 is circa 30x smaller

<br /><h4>x</h4>

= size of particulate matters