As an example, PPM suggests "elements per million". If you find out which the focus of NO2text NO _2NO2​ is equivalent to 1 ppm, it means that if you take a "sample" of air and divide it into 1,000,000 components, one of these will include NO2textual content NO _2NO2​. If https://donovanoleuj.pointblog.net/how-much-you-need-to-expect-you-ll-pay-for-a-good-free-ppm-calculator-83026087