As an example, PPM suggests "areas for each million". If you find out which the concentration of NO2textual content NO _2NO2​ is equal to 1 ppm, it means that if you're taking a "sample" of air and divide it into one million elements, one of these will encompass NO2text NO https://freeppmcalculator39371.blog-ezine.com/36924929/free-ppm-calculator-options