For instance, PPM implies "sections for each million". If you find out that the focus of NO2textual content NO _2NO2​ is equivalent to 1 ppm, it implies that if you take a "sample" of air and divide it into 1,000,000 pieces, one of these will include NO2textual content NO _2NO2​. https://paxtondjjjh.izrablog.com/37181939/rumored-buzz-on-free-ppm-calculator