For example, PPM suggests "areas for each million". If you find out which the concentration of NO2text NO _2NO2​ is equivalent to 1 ppm, it ensures that if you're taking a "sample" of air and divide it into 1,000,000 elements, one of them will encompass NO2text NO _2NO2​. Rijk is https://robinsong886fqa8.tokka-blog.com/profile