Such as, PPM means "parts for every million". If you find out which the concentration of NO2textual content NO _2NO2​ is equivalent to one ppm, it means that if you're taking a "sample" of air and divide it into a million areas, one of these will consist of NO2textual content https://onlineppmcalculator63951.aboutyoublog.com/43024529/the-smart-trick-of-ppm-calculator-that-no-one-is-discussing