How pure is the air in a cleanroom that is classification 1 according to ISO 14644-1, in which components such as semiconductors are manufactured? By themselves, the numbers (per cubic meter, there may be no more than 400 particles that are between 0.5 and 1μm) do not communicate much. To make them meaningful, we need a comparison.
One cubic meter of city air contains between 15 and 100 million particles of various sizes, and clean mountain air contains 10 million particles per cubic meter. In one cubic meter of air next to a smoker, there are up to 100 million particles larger than 0.5μm. This shows that cleanroom requirements for abrasion resistance are extreme and cannot be fulfilled with normal moving components.