Such as, PPM suggests "elements per million". If you find out that the focus of NO2textual content NO _2NO2​ is equal to 1 ppm, it implies that if you're taking a "sample" of air and divide it into a million components, one of them will consist of NO2textual content NO https://jaidenchebx.bloggactif.com/38097917/ppm-calculator-no-further-a-mystery