The column number density is measured in cm-2, and usually denoted using the symbol Q. It is defined by
where n is the particle density and m the particle mass. 1 m atm = cm-2. Additional units are the dobson unit = 10 m atm = cm-2, and 1 precipitable micron H2O = cm-2.
Column Mass Density, Law of Atmospheres, Number Density
