For example, PPM usually means "pieces per million". If you discover out the focus of NO2text NO _2NO2​ is equal to 1 ppm, it implies that if you are taking a "sample" of air and divide it into a million elements, one of them will include NO2textual content NO _2NO2​. https://ppmcalculator28371.timeblog.net/72435347/online-ppm-calculator-things-to-know-before-you-buy