By way of example, PPM signifies "elements for every million". If you find out which the focus of NO2text NO _2NO2​ is equal to one ppm, it means that if you are taking a "sample" of air and divide it into one million areas, one of them will encompass NO2textual https://felixjzocn.howeweb.com/37425283/the-best-side-of-free-ppm-calculator