One example is, PPM means "elements per million". If you discover out the concentration of NO2textual content NO _2NO2​ is equivalent to one ppm, it signifies that if you take a "sample" of air and divide it into one million sections, one of them will encompass NO2textual content NO _2NO2​. https://online-ppm-calculator48146.tusblogos.com/37038465/about-online-ppm-calculator