One example is, PPM implies "elements for each million". If you find out that the concentration of NO2text NO _2NO2​ is equal to one ppm, it signifies that if you're taking a "sample" of air and divide it into 1,000,000 parts, one of them will include NO2textual content NO _2NO2​. https://aesopz442scl2.aboutyoublog.com/profile