For example, PPM means "areas per million". If you find out which the concentration of NO2textual content NO _2NO2​ is equivalent to one ppm, it means that if you are taking a "sample" of air and divide it into a million elements, one of these will encompass NO2text NO _2NO2​. https://edgarlvusm.isblog.net/the-fact-about-online-ppm-calculator-that-no-one-is-suggesting-53795813