By way of example, PPM implies "sections for each million". If you discover out that the concentration of NO2text NO _2NO2​ is equivalent to 1 ppm, it ensures that if you take a "sample" of air and divide it into a million areas, one of them will include NO2text NO https://cristianvkvem.isblog.net/ppm-calculator-things-to-know-before-you-buy-53801768