As an example, PPM means "areas per million". If you find out the concentration of NO2textual content NO _2NO2​ is equal to 1 ppm, it ensures that if you are taking a "sample" of air and divide it into 1,000,000 parts, one of them will include NO2text NO _2NO2​. If https://freeppmcalculator41739.p2blogs.com/35433053/how-much-you-need-to-expect-you-ll-pay-for-a-good-online-ppm-calculator