Such as, PPM suggests "pieces for every million". If you discover out which the focus of NO2text NO _2NO2​ is equal to one ppm, it means that if you take a "sample" of air and divide it into 1,000,000 pieces, one of these will consist of NO2text NO _2NO2​. PPT https://johnathansitcl.idblogz.com/37168727/new-step-by-step-map-for-ppm-calculator