45ppm
45ppm denotes a concentration of 45 parts per million, meaning 45 units of a substance per one million units of the surrounding medium. In substance terms, 1 ppm is equal to 1 × 10^-6 of the mixture, so 45 ppm corresponds to 4.5 × 10^-5, or about 0.0045 percent.
ppm is used in two common contexts. For gases and vapors, ppm is usually a volume/volume measure
In practice, 45 ppm is a relatively dilute concentration and can be significant depending on the substance
Because ppm is a dimensionless ratio that depends on the matrix and conditions, specifying the substance and