Molar mass Molar mass In chemistry, the molar mass "M" is a physical property defined as the mass of a given substance (chemical element or chemical compound) divided by the amount of substance. The base SI unit for molar mass is kg/mol. However, for historical reasons, molar masses are almost always expressed in g/mol. In simple terms, molar mass of a substance is the total weight of that substance (in either kilogram or gram) for one mole of that substance. That is, the weight of a substance for 6.02214076×10^23 molecules or atoms of that substance. As an example, the molar mass of
Dobson unit Dobson unit should eventually be replaced by an appropriate SI unit and that the unit mmol m-2 was the most convenient and least cumbersome option. It expressed the hope that this unit would eventually supplant the Dobson Unit. However, as of March 2017, there is little evidence that this has occurred; for example the Dobson unit is still used by NASA and by the World Ozone and Ultraviolet Radiation Data Center in their reporting of total ozone amount. NASA uses a baseline value of 220 DU for ozone. This was chosen as the starting point for observations of the Antarctic