Such as, PPM means "elements per million". If you discover out that the focus of NO2text NO _2NO2​ is equivalent to 1 ppm, it signifies that if you are taking a "sample" of air and divide it into a million components, one of these will consist of NO2text NO _2NO2​. https://free-ppm-calculator58012.blog-kids.com/37002061/not-known-factual-statements-about-online-ppm-calculator