As an example, PPM implies "areas per million". If you find out that the focus of NO2text NO _2NO2​ is equivalent to one ppm, it means that if you are taking a "sample" of air and divide it into 1,000,000 elements, one of these will include NO2textual content NO _2NO2​. https://beaurjwhr.prublogger.com/35790496/free-ppm-calculator-no-further-a-mystery