is ppm a mass basis
Parts per million - ppm. ppm - parts per million - commonly used as a unit of concentration. Parts per million - ppm - is commonly used as a measure of small levels (concentrations) of pollutants in air, water, body fluids, etc. Parts per million is the mass ratio between the pollutant component and the solution - and ppm is defined as. ppm = 1000000 mc / ms.