By way of example, PPM usually means "parts per million". If you find out the focus of NO2textual content NO _2NO2​ is equal to 1 ppm, it ensures that if you're taking a "sample" of air and divide it into 1,000,000 components, one of these will consist of NO2textual content https://free-ppm-calculator08315.vidublog.com/35658810/top-latest-five-online-ppm-calculator-urban-news