Such as, PPM indicates "pieces for every million". If you find out the concentration of NO2text NO _2NO2​ is equivalent to 1 ppm, it ensures that if you are taking a "sample" of air and divide it into a million elements, one of these will encompass NO2textual content NO _2NO2​. https://online-ppm-calculator14690.blogspothub.com/35731318/the-smart-trick-of-free-ppm-calculator-that-no-one-is-discussing