One example is, PPM means "pieces for each million". If you find out the focus of NO2text NO _2NO2​ is equal to one ppm, it implies that if you take a "sample" of air and divide it into one million areas, one of these will include NO2text NO _2NO2​. If https://online-ppm-calculator20651.tusblogos.com/37039237/not-known-factual-statements-about-online-ppm-calculator