One example is, PPM indicates "components per million". If you find out which the concentration of NO2textual content NO _2NO2​ is equal to 1 ppm, it means that if you're taking a "sample" of air and divide it into 1,000,000 parts, one of these will encompass NO2textual content NO _2NO2​. https://pennf146shp4.wikisona.com/user