For instance, PPM means "elements for every million". If you discover out which 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 1,000,000 sections, one of these will consist of NO2text NO _2NO2​. https://ppm-calculator50258.bloggazzo.com/35646282/free-ppm-calculator-options