Avogadro constant Avogadro constant In chemistry and physics, the Avogadro constant, named after scientist Amedeo Avogadro, is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. Thus, it is the proportionality factor that relates the molar mass of a substance to the mass of a sample. The Avogadro constant, often designated with the symbol "N" or "L", has the value in the International System of Units (SI). (The parentheses there represent the degree of uncertainty.) Previous definitions of chemical quantity involved the Avogadro number, a historical term closely related to
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