For example, PPM implies "pieces per million". If you find out which the concentration of NO2textual content NO _2NO2​ is equal to one ppm, it implies that if you're taking a "sample" of air and divide it into 1,000,000 pieces, one of them will consist of NO2textual content NO _2NO2​. https://elenac813ige4.sunderwiki.com/user