As an example, PPM usually means "sections per million". If you find out the concentration of NO2textual content NO _2NO2​ is equivalent to 1 ppm, it signifies that if you are taking a "sample" of air and divide it into one million areas, one of these will include NO2textual content https://rylanylvfs.bligblogging.com/37423133/the-free-ppm-calculator-diaries