For instance, PPM usually means "parts for each million". If you discover out which the concentration of NO2text NO _2NO2​ is equivalent to 1 ppm, it signifies that if you take a "sample" of air and divide it into one million parts, one of them will include NO2text NO _2NO2​. https://finnwjkhe.laowaiblog.com/35619774/online-ppm-calculator-secrets