As an example, PPM usually means "parts per million". If you discover out the focus of NO2textual content NO _2NO2 is equal to 1 ppm, it means that if you take a "sample" of air and divide it into one million elements, one of them will include NO2textual content NO https://free-ppm-calculator88753.amoblog.com/online-ppm-calculator-secrets-58535053