By way of example, PPM usually means "sections for each million". If you find out which the focus of NO2text NO _2NO2​ is equivalent to one ppm, it implies that if you are taking a "sample" of air and divide it into a million areas, one of these will include https://onlineppmcalculator87418.blogolenta.com/33760002/new-step-by-step-map-for-free-ppm-calculator