As an example, PPM means "elements per million". If you discover out the concentration of NO2textual content NO _2NO2​ is equivalent to 1 ppm, it means that if you are taking a "sample" of air and divide it into one million parts, one of them will encompass NO2text NO _2NO2​. https://onlineppmcalculator37035.dailyblogzz.com/37298815/free-ppm-calculator-options