One example is, PPM indicates "areas per million". If you find out which the focus of NO2textual content NO _2NO2​ is equal to 1 ppm, it ensures that if you take a "sample" of air and divide it into a million sections, one of these will consist of NO2text NO https://paxtongjjgc.tinyblogging.com/free-ppm-calculator-options-80486013