Such as, PPM suggests "components per million". If you find out that the focus of NO2text NO _2NO2​ is equivalent to 1 ppm, it signifies that if you are taking a "sample" of air and divide it into a million sections, one of them will include NO2textual content NO _2NO2​. https://onlineppmcalculator67453.therainblog.com/35523884/a-secret-weapon-for-ppm-calculator