The number of ions per cubic metre and the highest particle size are used to estimate the amount of contamination in a modular cleanroom. To put things in perspective, the external environment is akin to a 5,000,000 class cleanroom. They're used in a variety of industries, including semiconductor production, biotechnology, life sciences, and other businesses that are very susceptible to environmental pollution. Get your cleanroom ASAP if you want a pollution free lab to work.