Such as, PPM signifies "areas for each million". If you discover out the concentration of NO2textual content NO _2NO2​ is equivalent to one ppm, it implies that if you are taking a "sample" of air and divide it into a million areas, one of these will include NO2text NO _2NO2​. https://freeppmcalculator61368.vblogetin.com/42561963/top-latest-five-online-ppm-calculator-urban-news