Parts Per Million (ppm)
Used to describe the amount of a trace element or substance present in the main substance.
Parts Per Million by Volume (ppmv)
Used to describe the amount of a trace element or substance present in the main substance as measured by volume.
Parts Per Million by Weight (ppmw)
Used to describe the amount of a trace element or substance present in the main substance as measured by weight.
See also: Volume Percentage.
