Such as, PPM signifies "areas per million". If you discover out that the focus of NO2textual content NO _2NO2​ is equivalent to 1 ppm, it means that if you're taking a "sample" of air and divide it into 1,000,000 sections, one of these will include NO2text NO _2NO2​. If percentages, https://onlineppmcalculator65295.techionblog.com/36815579/rumored-buzz-on-free-ppm-calculator